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924 terms

Geology Final Exam (The Complete Collection)

Everything. 924 Terms
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ATMOSPHERE
a layer consisting of a mixture of gases called air, surrounds our planet. Balloons rise because the gas in them is less dense than air.
wind
the flow of air from one place to another.
weather
the physical conditions (the temperature, pressure, moisture content, and wind velocity and direction) of the atmosphere at a given time and location.
climate
the average weather conditions during the year.
components of air
completely dry air consists of 78% nitrogen and 21% oxygen. The remaining 1% includes several gases in trace amounts: carbon dioxide and methane - greenhouse gases which allow solar radiation from the Sun to pass through, but trap infrared radiation from the Earth's surface.
aerosols
in addition to gases, the air contains trace amounts of ___. These tiny particles of liquid or solid material are so small that they remain suspended in the air. Include tiny droplets of water and acid and microscopic particles of sea salt, volcanic ash, clay, soot, and pollen.
acid rain
Pollutants within the air include sulfate and nitrate molecules, which react with water to make a weak acid that then falls from the sky as ___ ___.
air pressure
the push that air can exert on its surroundings, and air density therefore increase toward the surface of the Earth.
adiabatic cooling
when air moves from a region of higher pressure to a region of lower pressure, without adding or subtracting heat, it expands. When this happens, the air temperature decreases. Such a process is called ____ ____; air cools at 6 to 10 degrees C per kilometer that it rises.
adiabatic heating
if air moves from a region of lower pressure to a region of higher pressure, without adding or subtracting heat, it contracts, and the air temperature increases.
relative humidity
ratio between the measured water content and the maximum possible amount of water the air could hold, expresses as a percentage. Warmer air can hold more water than colder air. Water content in the air makes it either saturated or unsaturated.
dewpoint temperature
the temperature at which air becomes saturated is called the ___ _____; dew forms when under-saturated air cools at night and becomes saturated, so that water condenses on surfaces.
pauses
elevations where temperatures stop decreasing and start increasing or vice versa are called ___. These separate the Earth's atmosphere into four layers: troposphere, stratosphere, mesosphere, and the thermosphere.
troposphere
the layer closest to Earth, where almost all weather occurs; the thinnest layer; the air in this layer is constantly under convection.
stratosphere
the layer of the atmosphere that contains the ozone layer; temperature increases as you go up; air within this layer does not convect and thus remains stable and stratified, heating in this layer happens because ozone absorbs solar radiation.
mesosphere
the layer of the atmosphere between the stratosphere and the thermosphere and in which temperature decreases as altitude increases; this layer does not absorb much solar energy and thus cools with increasing distance from the hotter stratosphere below.
thermosphere
The uppermost layer of the atmosphere, in which temperature increases as altitude increases because gases of the thermosphere absorb short-wavelength solar energy; contains very little of the atmosphere's gas (less than 1%).
ionosphere
the layer of the atmosphere between 60 and 400 km, thus includes most of the mesosphere and the lower part of the thermosphere. In this layer, short-wavelength solar energy strips nitrogen molecules and oxygen atoms of their electrons and transforms them into positive ions. Plays an important role in modern communication.
isobar
a line on a map along which the air has a specified pressure is called an ___. In other words, the pressure is the same all along an these.
insolation
because the Earth is a sphere, not all areas receive the same amount of incoming solar energy, or ____: portions of the Earth's surface hit by direct rays of the Sun receive more energy per square meter than portions hit by oblique rays.
divergence zone
when the sinking air reaches low elevations, it divides, some moving back toward the equator near the surface and some moving north near the surface. A place where sinking air separates into flows moving in opposite directions is a ____ ___.
convergence zone
a place where two surface air flows meet so that air has to rise is called a _____ ___. This zone at latitude 60 deg. is called the 'polar front'
polar cells
where polar air sinks and flows away from the poles downward meeting the mid-latitude 'ferrel' cells at 60 degrees latitude.
prevailing winds
winds that blow in the same direction over large areas of Earth.
trade winds
Prevailing winds that blow northeast from 30 degrees north latitude to the equator and that blow southeast from 30 degrees south latitude to the equator.
doldrums
a belt of calms and light winds between the northern and southern trade winds of the Atlantic and Pacific, because air is mostly rising winds along the equator are very slow.
jet streams
because of the steepness of the gradient, high-altitude westerlies flow particularly fast. These zones of rapid movement, where winds typically flow at speeds of between 200 and 400 km per hour, are called __ ___.
weather system
a specific set of weather conditions, reflecting the configuration of air movement in the atmosphere, that affects a region for a period of time is called a ___ ___. They can move across the surface of the Earth, carried by prevailing winds.
air mass
a body of air, at least 1500 km across, that has recognizable physical characteristics is called an __ __. They move within the overall global circulation of the atmosphere, and their paths are controlled by prevailing winds.
front
the boundary between two air masses is called a ___. Three kinds: "cold", "warm", and "occluded".
wave cyclone
traveling cyclone of midlatitudes involving interaction of cold and warm air masses along sharply defined fronts.
fog
clouds that form at ground level make up __. Because clouds reflect and scatter incoming sunlight, they keep the ground cooler during the day, but at night they prevent infrared radiation from escaping, and thus keep the ground warmer.
condensation nuclei
droplets or ice grains clouds from by condensation or precipitation, respectively, when the air becomes saturated with water vapor. During cloud formation, water condenses on ______ ____, preexisting solid or liquid aerosols. Air can become saturated when evaporation provides additional water or when the air cools so that its capacity to hold water decreases.
lifting mechanisms
meteorologists recognize several conditions that cause air to rise: convective lifting, frontal lifting, covergence lifting, and orthographic lifting.
collision and coalescence
rain, snow, and sleet precipitate from clouds in two ways, depending on the temperature of the cloud. In warm clouds, rain develops by this process, during which the tiny droplets that compose the cloud collide and stick together to create a larger drop.
Bergeron process
precipitation involving the growth of ice crystals in a cloud at the expense of water droplets, is called the ___ ___.
cloud shapes
cumulus - puffy, cotton-ball-shaped; stratus - occur in relatively thin, stable layers, have a sheet/layered shape; cirrus - wispy shape, tapered feather-like curls.
storm
an episode of severe weather, when winds, rainfall, snowfall, and lightning become strong enough to be bothersome and/or dangerous. Form where large pressure gradients develop, producing strong winds.
hail
if updrafts in the cloud are strong enough, ice crystallizes in the higher levels of the cloud, where temperatures are below freezing, building into ice balls known as __.
lightning flash
air is a good insulator, so the charge separation can become very large until a giant spark or pulse of current jumps across the gap. We hear thunder that accompanies lightning because the immense energy of a flash almost instantaneously heats the surrounding air causing an explosion-like effect.
tornado and hurricane
a localized and violently destructive windstorm occurring over land characterized by a funnel-shaped cloud extending toward the ground; a huge, rotating storm, resembling a giant spiral in which sustained winds are greater than 119 km. Within these formations, air pressure becomes much lower because of the upward flow of air.
isotherms
lines that connect points that have the same temperature.
orographic barrier
a landform (such as a mountain range) that diverts airflow upward or laterally. This diversion affects the amount of precipitation and wind a region receives.
monsoon
a major reversal in the wind direction that causes a shift from a very dry season to a very rainy season. In southern Asia, people depend on these rains to bring moisture for their crops.
El Nino
(oceanography) a warm ocean current that flows along the equator from the date line and south off the coast of Ecuador at Christmas time.
southern oscillation
the atmospheric pressure conditions corresponding to the periodic warming of El Nino and cooling of La Nina.
DESERT
a region that is so arid (dry) that it contains no permanent streams, except for rivers that bring water in from temperate regions elsewhere, and supports vegetation on no more than 15% of its surface. In general, desert conditions exist where less than 25 cm of rain falls per year, on average.
subtropical deserts
types of deserts; from because of the pattern of convection cells in the atmosphere. Low latitude deserts, in the vicinities of the Tropics of Cancer and Capricorn, areas of high pressure and sinking air that is compressed and warmed.
rain shadow deserts
types of deserts; as air flows over the sea toward a coastal mountain range, the air must rise, expand and cool. The water it contains condenses and falls as rain on the seaward flank of the mountains, nourishing a coastal rain forest. As a consequence, this shadow forms, and the land beneath it becomes a desert.
desert varnish
a dark, rusty brown coating of iron oxide, manganese oxide, and clay covering the surface of many rock varieties in deserts.
arroyos (dry washes)
flash floods carve steep-sided channels into the ground. Scouring of bedrock walls by sand-laden water may polish the walls and create grooves. Dry stream channels in desert regions of the Western United States are called ____, and in the Middle East/North Africa they are called wadis.
suspended load
wind, just like flowing water, can carry sediment both as suspended load and as bed load; this load, with fine-grained sediment such as dust and silt held in suspension, floats in the air and moves with it.
saltation
moderate to strong winds can roll and bounce sand grains along the ground, a process called ____. This constitutes the wind's surface load, process begins when turbulence caused by wind shearing along the ground surface lifts sand grains.
lag deposit
in some cases, wind carries away so much fine sediment that pebbles and cobbles become concentrated at the ground surface. An accumulation of coarser sediment left behind when fine-grained sediment blows away is called __ ____.
desert pavement
in many locations, the desert surface resembles a tile mosaic in that it consists of separate stones that fit together tightly, forming a fairly smooth surface layer above a soil composed of silt and clay. Such natural mosaics constitute ___ ____.
ventifacts
rocks whose surface has been faceted by the wind are faceted rocks, or ____. Wind abrasion also gradually polishes and bevels down irregularities on a desert pavement and polishes the surfaces of desert-varnished outcrops, giving them a reflective sheen.
yardangs
in places where a resistant layer of rock overlies a softer layer of rock, wind abrasion may create a formation consisting of a resistant block perched on an eroding mushroom-like column of softer rock. These unusual features are called ____.
deflation
the process of lowering the land surface by wind erosion is called ____.
talus apron
under the influence of gravity, the resulting debris tumbles downslope and accumulates as a ___ ___ at the base of a hill. Typically see them fringing the bases of cliffs in deserts.
alluvial fan
the fan of distributaries spreads sediment, or alluvium, out into a broad ___ __, a wedge-shaped pile of sediment. These emerging from adjacent valleys may merge and overlap along the front of a mountain range, creating an elongate wedge of sediment called a bajada.
interior basin
where sufficient water flows into a desert basin, it creates a permanent lake. If the basin is an ___ ___, with no outlet to the sea, the lake becomes very salty, because although its water escapes by evaporation in the desert sun, its salt cannot.
playa
during drier times, desert lakes evaporate entirely, leaving behind a dry, flat lake bed known as a ___. Over time, a smooth crust of clay and various salts accumulates on the surface of these.
loess
much of the dust carried by desert wind is take out of the desert to accumulate elsewhere, forming layers of fine-grained sediment called ___.
dunes
sand being carried by desert wind, cannot travel far, and accumulates within the desert in piles called ___.
cliff retreat
in hilly regions, the lack of soil exposes rocky ridges and cliffs, cliffs erode when rocks split away along vertical joints. When this happens, the cliff face retreats but retains roughly the same form, the process, referred to as ___ ___, occurs in fits and starts.
cuestas
in places where bedding dips at an angle to horizontal, flat-topped mesas and buttes don't form; rather, asymmetrical ridges called ___ develop.
inselberg
with progressive cliff retreat on all sides of a hill, finally all that remains of the hill is this relatively small island of rock, surrounded by alluvium-filled basins.
pediments
bedrock surfaces extended outward like ramps from the steep cliffs of a mountain range on one side, to alluvium-filled valleys on the other. These are consequences of erosion, left behind as a mountain front gradually retreats.
sand dune
a pile of sand deposited by a moving current, form because of the wind in the desert. They start to form where sand becomes trapped on the windward side of an obstacle, such as a rock or a shrub. Types: barchan, transverse, longitudinal, parabolic, and star.
succulents
many desert plants have thick, fleshy stems and leaves. These plants are known as ____, can store water for long periods of time. Develop threatening needles or spines
desertification
the process of transforming nondesert areas to desert, has accelerated in modern times.
GLACIERS
slowly flowing masses of ice that survive the summer melt.
erratics
large boulders that have been transported into an area by a glacier.
ice age
Period of time when huge sheets of ice covered much of the earth's land, formed from ocean water, leaving ocean levels lower than they are now which exposed dry land that connected the continents.
mountain glaciers
accumulated snow at colder HIGHER elevations, snow turns to ice and flows to lower elevations where it melts.
cirques
bowl-shaped depressions on the flank of a mountain; valley glaciers, rivers of ice that flow down valleys.
continental glaciers
vast ice sheets that spread over thousands of square kilometers of continental crust.
temperate glaciers
glaciers occurring in regions where atmospheric temperatures become high enough during a substantial portion of the year for the glacial ice to be at or near its melting temperature throughout much of the year.
polar glaciers
occur in regions where atmospheric temperatures stay so low all year long that the glacial ice remains well below melting temperature throughout the entire year.
formation of glaciers
in order for glacial ice to form - the local climate must be sufficiently cold, must be sufficient snowfall for a large amount to accumulate, and the slope of the surface on which the snow accumulates must be gentle enough that the snow does not slide away in avalanches.
sublimate
the process of snow flakes evaporating directly into vapor, packs the snow more tightly as a result. As snow becomes buried, the weight of the overlying snow increases pressure, which causes remaining points of contact between snowflakes to melt. This process of melting at points of contact where the pressure is greatest is another example of pressure solution. Gradually, the snow transforms into a packed granular material called firn.
wet-bottom glaciers
glaciers move when meltwater accumulates at their bases, so that the mass of the glacier slides partially on a layer of water or on a slurry of water and sediment. Known as basal sliding, the water or wet slurry holds the glacier above the underlying rock and reduces friction between the glacier and its substrate. Is the dominant style of movement for these glaciers.
ice quakes
basal sliding motions of glaciers occur episodically - the ice stays fixed for a while until stress builds up sufficiently to cause the ice to lurch forward suddenly. This "stick-slip" generates __ ___.
dry-bottom glaciers
glaciers which move by means of internal flow, during which the mass of ice slowly changes shape internally without breaking apart or completely melting. Ice deforms plastically and the crystals slide past each other. These glaciers are so cold that their base remains frozen to their substrate.
crevasse
a large crack that develops by brittle deformation in a glacier is called a ___.
surge
if water builds up beneath a valley glacier to the point where if lifts the glacier off its substrate, the glacier undergoes a ___ and flows much faster for a limited time, until the water escapes.
ablation
the removal of ice by sublimation (the evaporation of ice into water vapor), melting, and calving (the breaking off of chunks of ice at the edge of the glacier) - subtracts from the account.
zone of accumulation and ablation
snowfall adds to the glacier in the zone of ___, whereas ablation subtracts in the zone of ___; the boundary between these two zones is the equilibrium line.
glacial advance
the leading edge or margin of a glacier is called its toe, or terminus. If the rate at which ice builds up in the zone of accumulation exceeds the rate at which ablation occurs below the equilibrium line, then the toe moves forward into previously unglaciated regions. Such a change is called a ___ ___.
glacial retreat
if the rate of ablation exceeds the rate of accumulation, then the position of the toe moves back toward the origin of the glacier; such a change is called a ___ ___. The position of the toe moves upslope.
ice shelves
continental glaciers entering the sea become broad, flat sheets called __ ____.
iceberg
if a free-floating chunk rises 6 m above the water and is at least 15 m long, it is formally called an ___.
drop stones
larger rocks that drop from the ice to the sea floor are called __ ___. In ancient glacial deposits, these appear as isolated blocks surrounded by mud.
glacially polished surfaces
a polished rock surface created by the glacial abrasion of the underlying substrate.
glacial striations
scratches and grooves on bedrock caused by glacial abrasion.
hanging valleys
shallow glacial valleys that met up with deep valleys.
fjords
the floors of valleys cut by coastal glaciers during the last ice age were cut much deeper than present sea level.
moraine
A ridge formed by the till deposited at the edge of a glacier. Unsorted material deposited along the sides of a valley glacier. If flowing water runs along the edge of the glacier and sorts the sediment of a lateral ____, a stratified sequence of sediment, called a kame, forms.
glacial drift
several different types of sediment can be deposited in glacial environments; types: glacial till, erratics, glacial marine, glacial outwash, glacial lake-bed sediment, loess.
loess
a fine-grained unstratified accumulation of clay and silt deposited by the wind.
glacial subsidence
the sinking of the surface of a continent caused by the weight of an overlying glacial ice sheet.
glacial rebound
the process by which the surface of a continent rises back up after an overlying continental ice sheet melts away and the weight of the ice is removed.
pluvial lakes
lakes that occur due to runoff accumulation from rainfall that does not evaporate.
permafrost
layer of permanently frozen subsoil in the tundra.
patterned ground
as a consequence of the freeze-thaw process, the ground splits into pentagonal or hexagonal shapes, creating a landscape called ___ ___. Water fills the gaps between the cracks and freezes to create wedge-shaped walls of ice.
glaciations
times during which the glaciers grew and covered substantial areas of the continents are called glacial periods, or ____, and times between glacial periods are called interglacial periods, or interglacials.
tillites
within the stratigraphic record, there are glacial deposits that have hardened into the rock. These deposits, called ____, consist of larger clasts distributed throughout a matrix of sandstone and mudstone. In many cases, these are deposited on glacially polished surfaces.
GLOBAL CHANGE
the transformations or modifications of both physical and biological components of the Earth System over time. There is gradual change over geologic time and catastrophic change which takes place relatively quickly. Unidirectional change involves transformations that never repeat, and cyclic change repeats the same steps over and over, though not necessarily with the same results.
biogeochemical cycle
the exchange of chemicals among living and nonliving reservoirs; some kinds of global change are due to changes in the proportions of chemical held in different reservoirs through time. Nonliving reservoirs include: the atmosphere, crust, and the ocean. Living reservoirs include: plants, animals, and microbes. The main two chemicals that are involved in this cycle are water and carbon.
global climate change
the transformations or modifications in Earth's climate over time, as well as the anthropogenic (human-caused) contributions over to global change.
supercontinent cycle
the process of change during which supercontinents form and later break apart. Geologists have found evidence that at least three or four times during the past 3 billion years of Earth history, supercontinents existed.
sedimentary sequence
throughout geologic time, when sea level rises the shoreline migrates inland and low-lying plains in the continents become submerged. During periods of particularly high sea level, more than half of the Earth's continental area can be covered by shallow seas; at such times, sediment buries continental regions, thereby changing their surface. When sea level falls, the continents become dry again, and regional unconformities develop - this blanket of sediment is called a ____ ____.
steady-state condition
for certain intervals of time, biogeochemical cycles attain a ___-___ _____, meaning that the proportions of a chemical in different reservoirs remain fairly constant even though there is a constant flux (flow) of the chemical among reservoirs.
global warming
if the average atmospheric and sea-surface temperature rises, we have ____ ____. Some changes are great enough to cause oceanic islands and large regions of continents to be submerged by shallow seas or to be covered by ice, whereas others are subtle, creating only a slight latitudinal shift in vegetation belts and a sea-level change measured in meters or less.
climate-change models
these provide insight into when and why climate changes took place in the past and whether they will happen in the future. Two basic approaches: researchers measure past climate change, indicated by the stratigraphic record, to document the magnitude of change that is possible and the rate at which such change occurred; also researchers develop computer programs to calculate how factors such as atmospheric composition, topography, ocean currents, and Earth's orbit affect the climate.
paleo-climate
past climate; these features can help to define these past climates: the stratigraphic record, paleontological evidence, oxygen-isotope ratios, bubbles in ice, growth rings, and human history.
greenhouse periods
geologists have reconstructed an approximate record of global climate, represented by mean temperature and rainfall, for geologic time. The record shows that at some times in the past, Earth's atmosphere was significantly warmer than it is today (____ ___); whereas at other times it was significantly cooler (ice ages).
causes of global climate change
What caused long-term global climate change? The answer probably lies in the complex relationships among the various geologic and biogeochemical cycles of the Earth system: positions of continents, volcanic activity, the uplift of land surfaces, formation of coal, oil, or organic shale, and life evolution.
runaway greenhouse effect
-occurs on Venus
-Venus is too close to the Sun to have liquid water oceans. Without water to dissolve CO2, it just gathers in the atmosphere.
factors of short-term climate change
fluctuations in solar radiation and cosmic rays - the amount of energy produced by the Sun varies with the sunspot cycle, changes in Earth's orbit and tilt, changes in volcanic emissions, changes in ocean currents, changes in surface albedo (reflectivity), and abrupt changes in concentrations of greenhouse gases.
mass-extinction events
the stratigraphic record shows that Earth history includes several of these - when large numbers of species abruptly vanish.
ecosystem
an interconnected network of organisms and the physical envrionment in which they live, is a product of evolution for an extended period of time.
ozone hole
an area of the ozone layer (near the poles) that is seasonally depleted of ozone. When emitted into the atmosphere, human-produced chemicals, most notably chlorofluorocarbons (CFCs), react with ozone in the stratosphere.
sustainable growth
an ability to prosper within the constraints of the Earth system - Economic growth and development that meets present needs without harming the needs of future generations.
ENERGY
provides the capacity to do work, to cause something to happen, or to cause change in a system.
energy resources
any item that can be employed for a useful purpose, more specifically something that can be used to produce heat, power muscles, produce electricity, or move vehicles.
fossil fuels (fuel)
(oil, gas, and coal) - combustible materials derived from organisms that lived in the past. Specifically they are matter that stores energy in a readily usable form.
sources of energy on Earth
(1) energy generated by nuclear fusion in the Sun and transported to Earth via electromagnetic radiation; (2) energy generated by the pull of gravity; (3) energy generated by nuclear fission reaction; (4) energy that has been stored in the interior of the Earth since the planet's beginning; (5) energy stored in the chemical bonds of compounds.
energy from the Sun
source of energy on Earth; (solar energy) can be converted directly to electricity, using solar panels, or it may used as heat water or to warm a house.
energy from gravity
source of energy on Earth; the gravitational attraction of the Moon, and the Sun, causes ocean tides of the sea surface. The flow of water in and out of channels during tidal changes can drive turbines.
both solar energy and gravity
source of energy on Earth; solar radiation heats the air, which becomes buoyant and rises. Thus, gravity causes cooler air to sink, the resulting air movement, wind, can power sails and windmills. When water condenses, it rains and falls on the land, where it accumulates in streams that flow downhill in response to gravity. This moving water powers waterwheels and turbines.
energy via photosynthesis
source of energy on Earth; green plants absorb some of the solar energy that reaches Earth's surface. With the aid of chlorophyll, plants produce sugar through a chemical reaction called photosynthesis. Burning plant matter in a fire releases potential energy stored in the chemical bonds of organic chemicals. Wood burning produces energy, and recently plant material (biomass) from crops such as corn and sugar cane has been used to produce ethanol, a flammable alcohol.
energy from chemical reactions
source of energy on Earth; a number of inorganic chemicals can burn to produce light and energy, energy resulting from exothermic reactions. Researchers have been studying electrochemical devices, such as hydrogen fuel cells, that produce electricity directly from these reactions.
energy from fossil fuels
source of energy on Earth; oil, gas, and coal come from organisms that lived long ago, and thus store solar energy that reached the Earth long ago. Burning these fuels produces energy in the same way that burning plant matter does.
energy from nuclear fission
source of energy on Earth; atoms of radioactive elements can split into smaller pieces. During this process, a tiny amount of mass is transformed into a large amount of energy, called nuclear energy. This type of energy runs nuclear power plants and nuclear submarines.
energy from Earth's internal heat
source of energy on Earth; Earth's internal energy dating back to the birth of the planet, while some is produced by radioactive decay in minerals. This internal energy heats water underground, the resulting hot water when transformed to steam, provides geothermal energy that can drive turbines.
hydrocarbons
oil and natural gas consist of these chainlike or ringlike molecules made of carbon and hydrogen atoms. These are considered to be a type of organic chemical, so named because similar chemicals make up living organisms. Products composed of short chains of molecules tend to be less viscous (they can flow more easily) and more volatile (they evaporate more easily) than products composed of long chains. Thus, short-chain molecules occur in gaseous form at room temperature, moderate-length-chain molecules as liquids, and long-chain molecules occur in solid form as tar.
oil and gas formations
the primary sources of the organic chemicals in oil and gas are dead algae and plankton. When algae and plankton die, they settle to the bottom of a lake or sea. Because their cells are so tiny, they can be deposited only in quiet-water environments in which clay also settles, so typically the cells mix with clay to create an organic-rich, muddy ooze; to be preserved it must be deposited in oxygen-poor water. Eventually, the resulting ooze lithifies and becomes black organic shale which contains raw materials from which hydrocarbons eventually form.
source rock
organic shale is referred to as ____ ___. Contains the raw materials from which hydrocarbons eventually form. These rocks are always sedimentary.
kerogen
if organic shale is buried deep enough (2 to 4 km), it becomes warmer, since temperature increases with depth in the Earth. Chemical reactions slowly transform the organic material in the shale into these waxy molecules called ___. Shale containing this is called oil shale.
oil window
if oil shale warms to temperatures of greater than about 90C, the kerogen molecules break down to form oil and natural gas molecules. At temperatures over 160C, any remaining oil breaks down to from natural gas, and at temperatures over 250C, organic matter transforms into graphite. Thus, oil itself forms only in this narrow range of temperatures. For regions with a geothermal gradient of 25C/km, this window lies at depths of about 3.5 km to 6.5 km, whereas gas can survive down to 9 km. Thus, hydrocarbon reserves can only exist in the topmost 15 to 25% of the crust.
hydrocarbon reserve
a known supply of oil and gas held underground. Currently countries bordering the Persian Gulf contain the world's largest reserves.
hydrocarbon system
a particular association of - source rock, reservoir rock, migratory pathway, and a trap - along with the processes of hydrocarbon generation, migration, and accumulation that ultimately produce a reserve from a given source, a system called the ____ ___.
hydrocarbon generation
geologists refer to the organic-rich shale as a source rock because it is the source for the organic chemicals that ultimately become oil and gas. If black shale resides in the oil window, the organic material within transforms into kerogen, and then into soil and gas. This process is ..
reservoir rocks
any organic matter in an oil shale remains trapped among the grains and can't move easily. Thus to obtain oil, companies drill into these rocks which contain (or could contain) an abundant amount of easily accessible oil and gas, meaning hydrocarbons that can be extracted out of the ground. Rocks with high porosity and permeability are the best.
pores
to be a reservoir rock, a body of rock must have space in which the oil or gas can reside, and must have channels through which the oil or gas can move. The space can be in the form of open spaces, or ___, between clastic grains or in the form of cracks and fractures that developed after the rock formed.
porosity
in some cases, groundwater passing through rock dissolves minerals and creates space, this refers to the amount of open space in a rock.
permeability
refers to the degree to which pore spaces connect to each other. In a permeable rock, the holes and cracks (pores) are linked, so a fluid is able to flow slowly through the rock, following a tortuous pathway.
migration pathway
to fill the pores of a reservoir rock, oil and gas must first migrate (move) from the source rock into a reservoir rock, which they will do over millions of years of geologic time. Hydrocarbons migrate because oil and gas are less dense than water, so they try to rise toward the Earth's surface to get above groundwater. Natural gas, being less dense, ends up floating above oil, thus buoyancy drives oil and gas upward. Typically, a hydrocarbon system must have a good ___ ___, such as a set of permeable fractures, in order for large volumes of hydrocarbons to move.
trap
if oil or gas escapes from the reservoir rock and ultimately reaches the Earth's surface, where it leaks away at an 'oil seep', there will be none left underground to pump. Thus, for an oil reserve to exist, oil and gas must be trapped underground in the reservoir rock, by means of a geologic configuration called a ___. A field contains one or more of these. There are four types: anticline, fault, salt-dome, and stratigraphic.
seal rock
a component to an oil/gas trap; a relatively impermeable rock such as shale, salt, or unfractured limestone, must lie above the reservoir rock and stop the hydrocarbons from rising further. Also, the seal and reservoir rock bodies must be arranged in a geometry that collects the hydrocarbons in a restricted area.
seismic-reflection profile
geologists, in their search for oil deposits, look for a region containing appropriate sedimentary rocks. Then they compile a geologic map of the area, showing the distribution of rock units. From this information, it may be possible to construct a preliminary cross section depicting the geometry of the sedimentary layers underground as they would appear on an imaginary vertical slice through the Earth. To construct this profile, a special vibrating truck or a dynamite explosion sends seismic waves into the ground, with such information the computer constructs an image of the configuration of underground rock layers.
rotary drills
once the decision has been made by a geologist, drillers go to work. Using ___ ___, they grind a hole down through rock. This type of drill consists of a rotating pipe tipped by a bit, a bulb of metal studded with industrial diamond or metal prongs. As the bit rotates, it scratches and gouges the rock, turning it into powder and chips.
derricks
drillers use these towers to hoist heavy drilling pipes. To drill in an offshore oil reserve, one that occurs in strata of the continental shelf, the derrick must be constructed on an offshore-drilling facility. These offshore drilling facilities can be more than 100 stories from the base to top. In shallower water, facilities anchor on the sea floor, but in deeper water, they float on huge submerged pontoons. Drill holes can be aimed in any direction, so drillers can reach many traps from the same facility.
pump
on completion of a hole, workers remove the drilling rig and set this up. Some resemble a bird pecking for grain, moving up and down to pull up oil that has seeped into the drill hole. Simple pumping gets only about 30% of the oil in a reservoir rock out of the ground. Thus, oil companies use secondary recovery techniques to coax out up to 50% more oil - creating artificial fractures or sourcing steam into the rock.
oil consumption
the U.S. is the largest consumer of oil (at a rate of 7 million barrels per day; 25% of the world's oil consumption), but lost its position as the largest producer in the 1970s. Oil reserves in the U.S. now account for only about 4% of the world total. Thus, today the United States must import more than half of the oil it uses.
distillation column
once extracted directly from the ground, "crude oil" flows first into storage tanks and then into a pipeline or tanker, which transports it to a refinery. At a refinery, workers distill crude oil into several separate components by heating it gently in a vertical pipe called a ___ ___. Lighter molecules rise to the top of the column. Chemical factories buy the largest molecules left at the bottom and transform them into plastics.
tar sand (or oil sand)
very viscous oil reserves (such as those in Alberta and Venezuela) consisting of tarlike "heavy oil". Known as bitumen, this oil has the consistency of molasses, and thus cannot be pumped directly from the ground. Sand or sandstone containing such high concentrations of bitumen is known as ___ ___.
biodegradation
the hydrocarbon system that leads to the generation of tar sands begins with the production and burial of a source rock in a large sedimentary basin. When subjected to temperatures of the oil window, the source rock yields oil and gas, which migrate into sandstone layers and then up the dip of tilted layers to the edge of the basin, where they become caught in stratigraphic traps. Over time, microbes attacked the oil reserve underground, digested lighter, smaller hydrocarbon molecules, and left behind only the larger molecules, whose presence makes the remaining oil so viscous. Geologists refer to such a transformation process as..
oil shale
vast reserves of organic-rich shale have not been subjected to temperatures of the oil window, or if they were, they did not stay within the oil window long enough to complete the transformation to oil, and thus still contain a high proportion of kerogen. Shale that contains at least 15-30% kerogen is called __ ___. It's not the same as coal, because the organic matter within exists in the form of hydrocarbon molecules, not as elemental carbon. It takes about 40% of the energy yielded by a volume of this to produce the oil.
natural gas
consists of volatile short-chain hydrocarbons, including: methane, ethane, propane, and butane. It occurs in the pores of reservoir rock above oil, because it "floats" over the oil. Where temperatures in the subsurface are so high that oil molecules break apart to form gas, gas-only fields develop. Burns more cleanly than oil (burning gas only produces primarily carbon dioxide and water)
gas hydrate
a chemical compound consisting of a methane molecule surrounded by a cage-like arrangement of water molecules. An accumulation of this produces a whitish solid that resembles ordinary water ice. Forms when anaerobic bacteria (bacteria living in the absence of oxygen) eat organic matter such as dead plankton that have been incorporated into the sea floor. Produce methane as a byproduct, and the methane bubbles into the cold seawater that fills pore spaces in sediments. Under pressures found at water depths greater than 300 m, the methane dissolves in water and produces these molecules.
coal
a black, brittle, sedimentary rock that burns, consists of elemental carbon mixed with minor amounts of organic chemicals, quartz, and clay. This and its counterpart, oil, do not have the same composition or origin. In contrast to oil, this forms from plant material (wood, stems, leaves) that once grew in coal swamps, regions that resembled the wetland and rain forests of modern tropical to semitropical coastal areas.
most extensive deposits of coal
occurred during the Carboniferous age. The abundance of Carboniferous coal reflects (1) the past position of the continents, warm climate in which vegetation flourished; (2) the height of sea level, at this time shallow seas bordered by coal swamps covered vest parts of continental interiors.
formation of coal
how the remains of plants transform into coal; the vegetation of an ancient swamp must fall and be buried in an oxygen-poor environment, so that it can be incorporated in a sedimentary sequence without first reacting with oxygen or being eaten. Compaction and partial decay of the vegetation transforms it into peat, which contains about 50% carbon, where deposits formed from moss and grasses in bogs during the last several thousand years.
transform peat into coal
transformation process; peat must be buried deeply (4-10 km) by sediment. Such deep burial can happen where the surface of the continent gradually sinks, creating a depression, or sedimentary basin, that can collect sediment. Sea level changes, transgression and regression, numerous peat layers in the sediment accumulate. Heat and pressure applied, chemical reactions occur destroying plant fibers and releasing hydrogen, nitrogen, and sulfur gases, once the proportion of carbon in the residue exceeds 70%, we have coal. With further burial and higher temperatures, chemical reactions remove additional hydrogen, nitrogen, and sulfur, yielding progressively higher concentrations of carbon.
coal transformation sequence
with increasing burial, peat transforms into a soft dark-brown coal called 'lignite'. At higher temperatures (about 100-200 C), lignite in turn, becomes dull, black 'bituminous coal'. At even higher temperatures (about 200-300 C), bituminous coal is transformed into shiny, black 'anthracite coal'. Formation requires high temperatures that develop only on the borders of mountain belts, so sediment ends up at depths of 8-10 km, where temperatures reach 300 C.
coal rank
as the carbon content of coal increases, we say the __ __ increases. The progressive transformation of peat to anthracite coal, which occurs as the coal layer is buried more deeply and becomes warmer, reflects the completeness of chemical reactions that remove water, hydrogen, nitrogen, and sulfur from the organic chemicals of the peat and leave behind carbon.
coal reserves
because the vegetation that eventually becomes coal was initially deposited in a sequence of sediment, coal occurs as sedimentary beds interlayered with other sedimentary rocks. To find coal, geologists search for sequences of strata that were deposited in tropical to semitropical, shallow-marine to terrestrial (fluvial or deltaic) environments - the environments in which a swamp could exist. The sedimentary strata of continents contain huge quantities of discovered coal, or __ ___.
strip mining
if the coal seam lies within 100 m of the ground surface, this method of mining proves to be the most economical. Miners use a giant shovel called a drag line to scrape off soil and layers of sedimentary rock above the coal seam. Once the seam is exposed, it then scrapes out the coal and dumps it into trucks.
underground mining
the only way deeper coal can be obtained. Miners dig shafts down to the depth of the coal seam and then create a maze of tunnels, using huge grinding machines that chew their way int the coal. Dangers include collapses, black lung, and methane explosion risks.
coalbed methane
the natural process by which coal forms underground yields large quanitities of methane, a type of natural gas. Over time, some of the gas escapes to the atmosphere, but vast amounts remain within the coal. Such ___ ___, trapped in strata too deep to be reached by mining, is a valuable energy resource that has become a target for exploration around the world. Obtaining this methane involves drilling instead of mining.
coal gasification
coal can be transformed into various gases, as well as solid byproducts, before burning, and the gases burn quite cleanly. The process of producing clean-burning gases from solid coal is called __ _____. Pulverized coal is contained, then a mixture of steam and oxygen passes through the coal at high pressure. The coal heats up to higher temperatures, chemical reactions break down the carbon molecules in coal and produce hydrogen. Solid ash, as well as sulfur and mercury, concentrate at the bottom of the container - the contaminants do not go up into the atmosphere.
nuclear fission
the breaking of the nuclear bonds that hold protons and neutrons together in the nucleus provides the energy. Fission occurs when a neutron strikes a radioactive atom, causing it to split; splitting an atom into smaller pieces. During this process, a tiny fraction of the matter composing the original atom is transformed into a large amount of thermal and electromagnetic energy. Just one gram of nuclear-reactor fuel yields as much energy as 2.7 barrels of oil.
nuclear reactor
first built to produce electricity during the 1950s. This is the heart of the nuclear plant, commonly lies within a dome-shaped shell (containment building) made of reinforced concrete. The reactor contains nuclear fuel packed into metal tubes called fuel rods. The pipe within the plant carry steam, produced from water near the heat-generating nuclear fuel, into a turbine where the rotation drives a dynamo that generates electricity.
chain reaction
the neutrons released during nuclear fission of one atom strike other atoms, thereby triggering more fission in a self-perpetuating process called a ___ ___.
geology of Uranium
U-235, an isotope of uranium containing 143 neutrons, is the most common fuel for conventional nuclear power plants. U-235 only accounts for about 0.7% of naturally occurring Uranium, thus to make a fuel suitable for use in a power plant, the U-235 concentration in a mass of natural uranium must be increased by a factor of 2 or 3, an expensive process called enrichment.
Uranium formation
uranium is concentrated by hot water percolating through a granitic pluton after intrusion dissolves the uranium and precipitates it, along with other elements, in cracks. Uranium from veins typically occurs in the mineral pitchblende (UO2). The world's richest uranium deposits occur in ancient stream-bed deposits. Prospectors use a Geiger counter to find uranium, an instrument that detects radioactivity.
meltdown
to order to maintain nuclear power plant safety, operators must constantly cool the nuclear fuel with circulating water, and the rate of nuclear fission must be regulated by the insertion of boron-steel control rods, which absorb neutrons and thus decrease the number of collision between neutrons and radioactive atoms. If left uncontrolled, so many neutrons begin to dash about in the fuel rods that the rate of fission becomes too fast and the fuel rods become too hot, in which case they melt and cause a..
nuclear waste
the radioactive material produced in a nuclear plant, includes spent fuel, which contains radioactive daughter products as well as water and equipment that may have been in contact with radioactive materials. Radioactive elements emit gamma rays and X-rays that can damage living organisms and cause cancer. Waste can sometimes remain dangerous for thousands of years or more; high-level waste contains greater than 1 million times the safe level of radioactivity, intermediate-level contains between 1 million and 1 thousand, and low-level waste contains less than 1 thousand times the safe level.
disposing of nuclear waste
nuclear waste cannot simply be stashed in a warehouse or buried in a town landfill, groundwater passing through the dump site might transport radioactive elements into municipal water supplies or nearby lakes/streams. Ideally, waste should be sealed in containers that will last for thousands of years, geoscientists have suggested these possibilities: underground mountain tunnels, interiors of impermeable salt domes, landfills surrounded by absorbent clay, landfills in regions where groundwater composition can react with radioactive atoms to form non movable minerals, the deep ocean floor where it can be subducted.
geothermal energy
refers to heat and electricity produced by using the internal heat of the Earth, exists because the Earth grows progressively hotter with depth. Produces energy in two ways: can simply pump hot groundwater out of the ground and run it through pipes to heat homes, elsewhere the groundwater is so hot that when it rises to the Earth's surface and decompresses, it turns to steam - which is used to drive turbines and generate electricity.
hydroelectric power
as water flows downslope, its potential energy converts into kinetic energy, the water flow drives turbines which drives generators that produce electricity. In order to increase the rate and volume of water flow in these dams, engineers build dams to create reservoirs that retain water and raise it to a higher elevation - the water flows through pipes down to turbines at the foot of the dam.
wind power
wind farms have been established around to world to generate electricity. The electricity is clean, but wind production requires the construction of large, noisy towers.
solar power
this energy is abundant but diffuse - on the sunniest of days, each square meter of the Earth surface receives about 1,000 watts of energy. How can this energy be concentrated sufficiently to produce heat and electricity? At present energy consumers have two options: solar collectors and photovoltaic cells.
solar collector
option for using solar power; a device that collects energy to produce heat, one class of these includes mirrors and lenses that focus light striking a broad area into a smaller area. Another class of collector consists of a black surface placed beneath a glass plate, the surface absorbs light passing through the plate and heats up. When a consumer runs water between the glass and the black surface, the water heats up and can then be stored in an insulated tank.
photovoltaic cells
option for using solar power; the use of these solar cells allows light energy to convect directly into electricity. Most PV cells consist of two wafers of silicon pressed together, silicon is a semiconductor meaning that it can conduct electricity only when doped with impurities; "doping" means that manufacturers intentionally add atoms other than silicon to the wafer. The two wafers are doped with arsenic and boron, when light strikes the cell, the electrons gain energy to cross the boundary and an electrical current flows.
biofuels
in recent years, farmers have begun to produce rapidly growing crops specifically for the purpose of creating biomass for fuel production. The resulting liquids are ___.
production of ethanol
the most commonly used biomass fuel; produced from the fermentation of sugar derived from corn or sugar cane. Production includes three steps: (1) grain is grinded into a fine powder, mixed with water, and cooked to produce a mash of starch; (2) farmers add an enzyme to the mash, which converts the mash into sugar; (3) they mix in yeast and allow it to ferment; (4) the fermented mash is then distilled to concentrate the ___.
fuel cells
in a __ __, chemical reactions produce electricity directly. In a hydrogen fuel cell, hydrogen gas flows through a tube across an anode (a strip of platinum) that has been placed in a water solution containing an electrolyte. At the same time, a stream of oxygen gas flows onto a separate platinum cathode that also has been placed into the solution, a wire connects the anode and the cathode to create an electrical circuit. In this configuration, hydrogen reacts with oxygen to produce water, about 40-80% of the chemical energy released by this reaction produces electricity, the rest becomes heat.
Oil Age
Oil is finite and non-renewable so there will be an end to this age. It takes millions of years for oil to generate and humans are using it all in mere centuries.
acid rain
rain containing acids that form in the atmosphere when industrial gas emissions (especially sulfur dioxide and nitrogen oxides) combine with water. A dilute solution of sulfuric acid produced when sulfur-bearing minerals such as pyrite in mines can react with rainwater. The runoff enters streams and kills fish and plants.
MINERAL RESOURCES
minerals extracted from the Earth's upper crust that are of use to civilization. Without these resources, industrialized societies could not function. Two categories: metallic (rocks containing gold, copper, aluminum, iron) and nonmetallic (building stone, gravel, sand, gypsum, phosphate, salt).
metals
opaque, shiny smoot solids that can conduct electricity and can be bent, drawn into wire, or hammered into thin sheets. They look and behave quite differently from wood, plastic, meat, or rock. Unlike other substances, the atoms that make up metals are held together by metallic bonds, meaning that the outer electrons flow from atom to atom fairly easily.
native metals
certain metals - namely, copper, silver, gold, and mercury - can occur in rock as ___ ___. Consist of only metal atoms, and thus look and behave like metal.
smelting
most of the metal atoms we use today originated as ions bonded to nonmetallic elements in a great variety of minerals that themselves look nothing like metal. Only because of the chance discovery by some prehistoric genius that certain rocks, when heated to high temperatures in fire, a process called ___, decompose to yield metal plus a nonmetallic residue called slag do we now have the ability to produce sufficient metal for the needs of industrialized society.
alloy
a compound containing two or more metals
copper
of the three principle metals used today, this began to be used first, because copper smelting from sulfide minerals is relatively easy. Can be mixed with tin to produce bronze, an alloy whose strength exceeds that of either metal alone, and warriors came to rely on bronze for their swords.
iron
of the three principle metals, this one proved superior to copper or bronze for many purposes because of its strength, hardness, and abundance. Has a very high melting temperature that can be difficult to reach, in addition, the metal generally occurs in ___-oxide minerals and liberation of iron metal from oxide minerals requires a chemical reaction, not just simple heating.
aluminum
one of the three principle metals used; is abundant in rocks of the crust and, in many ways, is preferable to iron because it weighs less. But is does not occur in native form, and the extraction of ____ from minerals requires complex methods.
precious metals
classification of metal; gold, silver, platinum
base metals
classification of metal; copper, lead, zinc, and tin
ore
to obtain the metals needed for industrialized society, we mine __, rocks containing a concentrated accumulation of native metals or __ minerals.
ore minerals (or economic minerals)
minerals that contain metal in high concentrations and in a form that can be easily extracted. Galena, for example, is about 50% lead, so we consider it to be an __ ___ of lead. We obtain most of our iron from the oxide minerals, hematite and magnetite.
grade (of the ore)
to be an ore, a rock must not only contain ore minerals, it must also have a sufficient amount to make it worth mining. Iron constitutes about 6.2% of the continental crust's weight, whereas it makes up about 30 to 60% of iron ore. The concentration of a useful metal in an ore determines the ___ of the ore - the higher the concentration, the higher this is.
ore deposit
an economically significant occurrence of ore. The various kinds of __ ___ differ from each other in terms of which ore minerals they contain and which kind of rock body they occur in.
magmatic deposit
when magma cools, sulfide ore minerals crystallize early and then, because sulfides tend to be dense, sink to the bottom of the magma chamber, where they accumulate; this accumulation is a ____ ____.
massive-sulfide deposit
when the magma freezes solid within a magmatic deposit, the resulting igneous body may contain a solid mass of sulfide minerals at its base. Because of their composition, we consider these masses to be a type of..
hydrothermal deposit
hydrothermal activity dissolves metal ions, when a solution enters a region of lower pressure, lower temperature, different acidity, and/or different availability of oxygen, the metals come out of solution and form ore minerals that precipitate in fractures and pores, creating a ____ ___. Such deposits may form within an igneous intrusion or in surrounding country rock.
disseminated vs. vein (hydrothermal deposits)
from the process of a hydrothermal deposit, if the resulting ore minerals disperse through the intrusion, we call the deposit a ___ deposit. But if they precipitate to fill cracks in preexisting rock, we call the deposit a __ deposit.
secondary-enrichment deposits
a new ore deposit formed from metals that were dissolved and carried away from a preexisting ore deposit. Some of these deposits contain spectacularly beautiful copper-bearing carbonate minerals, such as azurite and malachite.
banded-iron formations
iron-rich sedimentary layers, because after lithification they consist of alternating beds of gray iron oxide (magnetite or hematite) and red beds of jasper (iron-rich chert). Microbes may have participated in the precipitation process.
manganese nodules
the chemistry of seawater in some parts of the ocean today leads to the deposition of managese-oxide minerals on the sea-floor. These minerals grow into lumpy accumulations known as ____ ___.
residual mineral deposits
in rainy, tropical environments, the residuum left behind in soils after leaching includes concentrations of iron or aluminum. Locally, these metals become so concentrated that the soil itself becomes an ore deposit. For example, most of the aluminum ore mined today comes from bauxite, a ___ ___ ___ created by the extreme leaching of rocks (granite) containing aluminum-bearing minerals.
placer deposit
concentrations of metal grains in stream sediments are a type of ___ ___. The heavy metal grains in a stream accumulate in sand or gravel bars, for the moving water carries away lighter mineral grains but can't move the metal grains so easily.
ore formation
ores from by: settling from melt, precipitating from hot water, deposition from currents, alteration by groundwater, and extreme weathering. The distribution of ores can be explained by plate tectonics, they occur along boundaries.
open-pit mine
miners use giant earth moving equipment to dig a huge pit and remove ore deposits. Workers then separate ore minerals from other minerals and send the concentrate to a processing plant, where it undergoes smelting or treatment with acidic solutions to separate metal atoms from other atoms. Eventually, workers melt the metal and then pour it into molds to make ingots for transport to a manufacturing facility.
underground mine
mine below the surface of the Earth; , best mining technique for deeper deposits in horizontal layers, more than about 100 meters below.
dimension stone
intact slabs and blocks of rock (such as granite or marble); sedimentary, metamorphic and igneous rocks that can be cut in different sizes. Used for decorative rock for the face of buildings, floors and roof tops.
mortar vs. concrete
__ refers to the substance that holds bricks or stone blocks together, whereas __ refers to the substance that workers shape into roads or walls by spreading it out into a layer or by pouring it into form. The cement in either starts out as a powder composed of lime, quartz, aluminum oxide, and iron oxide.
Portland cement
since natural limestone with the exact composition of cement is relatively rare, most cement used today is ___ ___, made by mixing limestone, sandstone, and shale in just the correct proportions to provide the correct chemical makeup.
crushed stone
any variety of coherent rock (limestone, quartzite, granite, gneiss); forms the substrate of highways and railroads and is the raw material for manufacturing cement, concrete, and asphalt. In these quarries, operators use high explosives to break up bedrock into rubble that they then transport by truck to a jaw crusher, which reduces the rubble to usable-size fractions.
limestone
sedimentary rock made of calcite; used for gravel or cement
siltstone
beds of sedimentary rock; used to make flagstone
granite
coarse igneous rock; used for dimension stone
marble
metamorphosed limestone; used for dimension stone
slate
metamorphosed shale; used for roofing shingles
gypsum
a sulfate salt precipitated from saltwater; used for wallboard
phosphate
from the mineral apatite; used for fertilizer
pumice
frothy volcanic rock; used to decorate gardens and paths
clay
very fine mica-like material in sediment; used to make bricks or pottery
sand
from sandstone, beaches, or riverbeds; quartz sand is used for construction and for making glass
salt
from the mineral halite, formed by evaporating saltwater; used for food, melting ice on roads
sulfur
occurs either as native sulfur, typically above salt domes, or in sulfide minerals; used for fertilizer and chemicals
reserves
mineral resources, like oil and coal, are nonrenewable resources. Once mined, an ore deposit or a limestone hill disappears forever, natural geologic processes do not happen fast enough to replace the deposits as quickly as we use them. Geologists have calculated ___ (measured quantities of a commodity) for various mineral deposits just as they have for oil. Based on current definitions of these and rates of consumption, supplies of some metals may run out in only decades to centuries.
strategic metals
include manganese, platinum, chromium, and cobalt - metals alloyed with iron to make the special-purpose steels needed in the aerospace industry. Principal reserves of these metals lie in the crust of countries that have not always practiced open trade with the U.S., as a defense precaution the U.S. stockpiles these metals.
MASS MOVEMENT
geologists refer to the gravitationally caused downslope transport of rock, regolith (soil, sediment, and debris), snow, ice as __ ___, or mass wasting. They are the most costly natural hazard, also they play a critical role in the rock cycle, for it's the first step in the transportation of sediment. It's the most rapid means of modifying the shapes of slopes.
natural hazard
like earthquakes, volcanic eruptions, storms, and floods, mass movements are a type of ___ ___, meaning a natural feature of the environment that can cause damage to living organisms and to buildings.
4 factors of mass movement
geologists distingiush among different types of mass movement on the basis of these factors: the type of material involved (rock, regolith, or snow or ice), the velocity of the movement (fast, intermediate, or slow), the character of the moving mass (chaotic cloud, slurry, or coherent body), and the environment in which the movement takes place (subaerial or submarine).
creep
during the spring thaw, water becomes liquid again, and gravity makes the particles sink vertically and thus migrate downslope lightly. This gradual downslope movement of regolith is called ___. Happens over a period of years it causes trees, fences, gravestones, walls, and foundations built on a hillside to tilt downslope.
solifluction
Slow, downslope flow of water-saturated materials common to permafrost or tundra (cold, treeless ragions) areas.
rock glaciers
another type of slow mass movement in cold regions takes place in __ ___, which consist of a mixture of rock fragments and ice, with the rock fragments making up the major proportion. These develop where the volume of debris falling into a valley equals or exceeds the volume of glacial ice forming from snow.
failure surface
during slumping, a mass of regolith detaches and slips semicoherently downslope. We call the moving mass itself a slump, and the surface on which it slips a ___ ___. On average, the sea cliffs of southern California retreat (move inland) by up to a few meters a year because of slumping.
head scarp
the distinct, curving step at the upslope edge of a slump, where the regolith detached, is called a __ __. Immediately below this, the land surface sinks below its previous elevation. Farther downslope, at the end of the slump, the ground elevation rises as the slump mass rides up and over the preexisting land surface. The end (the toe) may break into a series of slices that form curving ridges at the ground surface.
mudflow
in areas such as hill-slope communities of Rio, where neither vegetation nor drainage systems protect the ground from rainfall, water mixes with regolith to create a slurry that moves downslope. If the slurry consists of just mud, it's a ___, but if the mud is mixed with larger rock fragments, it's a debris flow.
lahars
particularly devastating mudflows spill down the river valleys bordering volcanoes. These mudflows, known as ___, consist of a mixture of volcanic ash from a currently erupting or previously erupted pyroclastic cloud, and water from the snow and ice that melts in a volcano's heat or from heavy rains.
landslide
geologists refer to the sudden movement of rock and debris down a nonvertical slope as a ___. If the mass consists only of rock, it may also be called a rock slide, and if it consists mostly of regolith, it may also be called a debris slide. Once one has take place, it leaves a scar on the slope and forms a debris pile at the base of the slope.
landslide occurrence
slides happen when bedrock and/or regolith detaches from a slope and shoots downhill on failure surface roughly parallel to the slope surface. Thus, landslides generally occur where a weak layer of rock or sediment at depth below the ground parallels the land surface. Slides may move at speeds up to 300 km per hour; they are particularly fast when a cushion of air gets trapped beneath, so there is virtually no friction between the slide and its substrate, and the mass moves like a hovercraft.
avalanche
turbulent clouds of debris mixed with air that rush down steep hill slopes at high velocity. If the debris consists of snow, like the Austrian one, it's a snow ____. If it consists of rock and dust, it's a debris ____. The moving-air debris mass is denser than clear air, thus it hugs the ground and acts like an extremely strong and viscous wind that can knock down and blow away anything in its path.
rockfalls
these happen when large blocks of rock break loose from a cliff face, or steep slope, along a joint and start tumbling.
debris falls
Type of slope failure that occurs when a mixture of soil, regolith, and rocks becomes dislodged and falls down the slope.
talus
a sloping mass of loose rocks at the base of a cliff; friction and collision with other rocks may bring some blocks to a halt before they reach the bottom of the slope.
submarine slumps
form of submarine mass movement; semicoherent blocks (olistostromes) slip downslope on weak mud detachments. In some cases, the layers constituting the blocks become contorted as they move, like a tablecloth that has slid off a table.
submarine debris flows
type of submarine mass movement; the moving mass breaks apart to form a slurry containing larger clasts (pebbles to boulders) suspended in a mud matrix.
turbidity currents
type of submarine mass movement; sediment disperses in water to create a turbulent cloud of suspended sediment that avalanches downslope. As this current slows, sediment settles out in sequence from coarse to fine, creating graded beds.
cause of mass movements
in order for these movements to take place, the stage must be set by the following phenomena; fracturing and weathering, which weaken materials at Earth's surface so that they cannot hold up against the pull of gravity; and the development of relief, which provides slopes down which masses move. The velocity of these movements depends on the steepness of the slope and the water or air content of the mass.
angle of repose
what causes resistance force? Chemical bonds in mineral crystals, cement, and the interlocking of crystals hold intact rock in place, friction holds an unattached block in place, electrical charges and friction hold dry regolith in place, and surface tension holds slightly wet regolith in place. Because of resistance force, granular debris tends to pile up and create the steepest slope it can without collapsing. The angle of this slope is called the __ _ ___, and for most dry, unconsolidated materials (such as dry sand) it typically has a value between 30 and 37 degrees.
slope failure surfaces
in many locations, the resistance force is less than might be expected because a weak surface exists at some depth below ground level. This weak surface separates unstable rock and debris above from the substrate below. These include: wet clay layers, wet unconsolidated sand layers, surface-parallel joints (exfoliation joints), weak bedding planes (shale and evaporite beds), and metamorphic foliation planes.
quick clay
groundshaking produces a unique effect in certain types of clay. This clay consists of damp clay flakes, behaves like a solid when still, for surface tension holds water-coated flakes together. But shaking separates the flakes from one another and suspends them in the water, thereby transforming the clay into a slurry that flows like a fluid.
liquefaction
The process by which an earthquake's violent movement suddenly turns loose soil into liquid mud.
dip slope
when bedding on a mountain parallels the face of the mountain itself.
undercutting
in some cases, excavation results in the formation of an overhang. When such ____ has occurred, rock making up the overhang eventually breaks away from the slope and falls. Overhangs commonly develop above a weak horizontal layer that erodes back preferentially, or along seacoasts and rivers where the water cuts into a fairly strong slope.
landslide-potential maps
identify slide prone areas and potentially unstable slopes. The factors considered include: slope steepness, strength of substrate, degree of water saturation; orientation of bedding, joints, or foliation relative to the slope; nature of vegetation cover; potential for heavy rains; potential for undercutting to occur; and likelihood of earthquakes in an area.
riprap
loose boulders or concrete
preventing mass movements
in areas where hazard exists, people can take certain steps to remedy the problem and stabilize the slope: re-vegetation, regrading, reducing subsurface water, preventing undercutting, constructing safety structures, and controlling blasting of unstable slopes.
RUNNING WATER
water that flows down the surface of sloping land in response to the pull of gravity.
stream
geologists use this term for any channelized body of running water, meaning water that flows along a channel, an elongate depression or trough.
flood
generally, a stream stays within the confines of its channel , but when the supply of water entering a stream exceeds the channel's capacity, water spills out and covers the surrounding land, thereby causing a ___, such as the one that washed away Johnstown.
runoff
the portion of meteoric water that eventually ends up in streams, includes water that has passed through a variety of surface and subsurface reservoirs in the hydrologic cycle.
sky
type of runoff pathway; some water falls directly from the __ onto the surface of a stream. Generally, this water makes only a small contribution to a stream's volume.
standing body
type of runoff pathway; in places where the ground surface is flat or forms a depression, water accumulates in a ___ ___ (puddle, swamp, pond, lake). When the water level in the standing body becomes higher than the lowest point along the body's bank, an outlet forms, through which water spills into a stream.
sheetwash
type of runoff pathway; on slopes, water can move as ____ - a thin film up to a few millimeters thick - down the ground surface to a lower elevation. This water either enters a stream directly or first enters a standing body and later flows through an outlet into a stream.
subsurface water
type of runoff pathway; where the ground surface is permeable, water can infiltrate down and become ____ ___. Includes soil, moisture, vadose-zone water (water that partially fills cracks and pores in rock or regolith below the soil but above the water table), and groundwater (water that completely fills cracks and pores in the region below the water table)
downcutting
the process of eroding or digging into substrate. The efficiency of this process depends on several factors: (1) the velocity of flow, (2) the strength of the substrate, for weaker substrate can be eroded more rapidly than stronger substrate, (3) the amount of vegetation cover, for unvegetated ground can be eroded more rapidly than land held together by plant roots.
headward erosion
as flow increases, a stream channel also begins to lengthen up its slope, a process called ___ ___. This occurs because the flow is more intense at the entry to the channel (upslope) than in the surrounding sheetwashed areas.
tributaries
an array of linked streams evolves, with the smaller streams, or ____, flowing into a single larger stream, or 'trunk stream'. The array of interconnecting streams together constitute a drainage network. These networks reach into all corners of a region, providing conduits for the removal of runoff. The configuration of these streams defines the map pattern of a drainage network, this pattern depends on the shape of the landscape and the composition of the substrate.
dendritic
type of stream pattern; when rivers flow over a fairly uniform substrate with a fairly uniform initial slope, they develop a ____ network, which looks like a pattern of branches connecting to the trunk of a deciduous tree.
radial
type of stream pattern; drainage networks forming on the surface of a cone-shaped mountain flow outward from the mountain peak, like spokes on a wheel. Such a pattern defines a ___ network.
rectangular
type of stream pattern; in places where a rectangular grid of fractures, (vertical joints) breaks up the ground, channels form along the preexisting fractures, and streams join each other at right angles, creating a ____ network.
trellis
type of stream pattern; in places where a drainage network develops across a landscape of parallel valleys and ridges, major tributaries flow down a valley and join a trunk stream that cuts across the ridges; the place where a trunk stream cuts across a resistant ridge is water gap. The resulting map pattern resembles a garden trellis, so the arrangement of streams constitutes a ___ network.
watershed
a drainage network collects water from a broad region, variously called a drainage basin, catchment, or ____, and feeds it into the trunk stream, which carries the water away.
drainage divide
the highland, or ridge, that separates one watershed from another is a ___ ___. A continental divide separates drainage that flows into one ocean from drainage that flows into another.
permanent streams
the character of a stream depends on the depth of the water table. If the bed, or floor, of a stream lies below the water table, then the stream flows year-round. In such ____ ___, found in humid or temperate climates, water comes not only from upstream or from surface runoff, but also from springs through which groundwater seeps. But if the bed of a stream lies above the water table, then water flows only when the rate at which water enters the stream channel exceeds the water infiltration rate below the channel.
ephemeral streams
in dry climates with intermittent rainfall and high evaporation rates, water entirely sinks into the ground, and the stream dries up when the supply of water stops. Streams that do not flow all year are called ___ ___. They only flow during rainstorms or after springs thaws. A dry ____ ___ bed (channel floor) is called a dry wash, wadi, or arroyo.
discharge
geologists and engineers describe the amount of water a stream carries by its ____, the volume of water passing through an imaginary cross section drawn across the stream perpendicular to the bank, in a unit of time. This depends on two factors: the cross-sectional area of stream and the average velocity at which water moves in the downstream direction. Is determined at a stream-gauge station.
thalweg
the deepest part of a channel
turbulence
turbulent flow, is a twisting, swirling motion that, on a large scale, can create eddies (whirpools) in which water curves and actually flows upstream or circles in place. Develops in part because the shearing motion of one volume against its neighbor causes the neighbor to spin, and in part because obstacles such as boulders deflect volumes, forcing them to move in a different direction.
scouring
type of stream erosion; running water can remove loose fragments of sediment, a process called ___.
breaking and lifting
type of stream erosion; the push of flowing water can break chunks of solid rock off the channel floor or walls. In addition, the flow of a current over a clast can cause the clast to rise, or lift off the substrate.
abrasion
type of stream erosion; sand-laden water acts like sandpaper and grinds or rasps away at the channel flood and walls, a process called ___. In places where turbulence produces long-lived whirpools, this process by sand or gravel carves a bowl-shaped depression, called a pothole, into the floor of the stream.
dissolution
type of stream erosion; running dissolves soluble minerals as it passes, and carries the minerals away in solution.
dissolved load
type sediment load of streams; running water dissolves soluble minerals in the sediment or rock of its substrate, and groundwater seeping into a stream through the channel walls brings dissolved minerals with it. These ions constitute a stream's ___ ___.
suspended load
type of sediment load of streams; the ____ __ of a stream consists of tiny solid grains (silt or clay size) that swirl along with the water without settling to the floor of the channel; this sediment makes the water brown.
bed load
type of sediment load of streams; the __ __ of a stream consists of large particles (such as sand, pebbles, or cobbles) that bounce or roll along the stream floor. Typically, this movement involves saltation, a process during which grains on the channel floor get knocked into the water column momentarily, follow a curved trajectory downstream, and gradually sink to the bed again, where they knock other grains into the water column.
competence
the ___ of a stream refers to the maximum particle size it carries; a stream with high ___ can carry large particles, whereas one with low ___ can carry only small particles. A fast-moving, turbulent stream has more than a slow-moving stream, and a stream in flood has more than a stream with normal flow.
capacity
the ___ of a stream refers to the total quantity of sediment it can carry. Depends upon its competence and discharge.
alluvium
geologists refer to sediments transported by a stream as fluvial deposits or ___. Fluvial deposits may accumulate along the stream bed in elongate mounds, called 'bars'.
delta
a wedge of sediment called a ___, accumulates.
stream gradient
the slope of a stream channel
longitudinal profile
a cross-sectional image showing the variation in the river's elevation along its length, is roughly a concave-up curve. This curve illustrates that stream gradient is steeper near its headwaters (source) than near its mouth.
base level
streams progressively deepen their channels by downcutting, but there is a depth below which a stream cannot downcut any further. The lowest elevation a stream channel's floor can reach at a locality is the __ __ of the stream. A local one occurs upstream of a drainage network's mouth, and the ultimate __ __ (the lowest possible elevation along the stream's longitudinal profile) is determined by sea level.
V-shaped valley
valleys eroded due to fast flowing water often found in upland areas
stream terraces
if the stream's base level then drops again and/or the discharge increases, the stream will start to cut down into its own alluvium, a process that generates ___ ___ bordering the present floodplain.
rapids
particularly turbulent water with a rough surface.
waterfall
forms when the gradients of a stream becomes so steep that the water literally free-falls down the stream bed.
alluvial fan
where a fast-moving stream abruptly emerges from a mountain canyon into an open plain at the range front, the water that was once confined to a narrow channel spreads out over a broad surface. As a consequence, the water slows and abruptly drops its sedimentary load, forming a gently sloping apron of sediment (sand, gravel, and cobbles) called an ___ __.
braided stream
in some localities, streams carry abundant coarse sediment during floods but cannot carry this sediment during normal flow. Thus, during normal flow, the sediment settles out and chokes the channel. As a consequence, the stream divides into numerous strands weaving back and forth between elongate bars of gravel and sand. The result is a ___ __ - the name emphasizes that the streams entwine like strands of hair in a braid.
meanders
A winding, looping curve in the course of a river on soft, flat flood plain. Increases the volume of the stream by increasing its length.
oxbow lake
in a natural meandering river system, the river channel migrates back and forth across the floodplain. When erosion eats through a meander neck, a straight reach called a cutoff develops. The meander that has been cut off is called an ___ __ if it remains filled water, or an adandoned meander if it dries out.
floodplain
a low plain adjacent to a river that is formed chiefly of river sediment and is subject to flooding. During a flood, water spills out from the stream channel onto this, and large floods may cover the entire region from bluff to bluff. As the water leaves the channel, friction between the ground and the thin sheet of water moving over the floodplain slows down the flow. This slowdown decreases the competence of the running water, so sediment settles out along the edge of the channel.
natural levees
over time, the accumulation of this sediment creates a pair of low ridges, called __ __, on either side of the stream. They may grow so large that the floor of the channel may become higher than the surface of the floodplain.
distributaries
along most of its length, only a narrow floodplain - green, irrigated farm fields - borders the Nile River in Egypt. But at its mouth, the trunk stream of the Nile divides into a fan of smaller streams, called ____, and the area of green agricultural lands broadens into a triangular patch.
stream rejuvenation
where streams cut down into landscape that was originally near the stream's base level, ___ ____ has occurred. This happens when the base level of a stream drops, when land rises beneath a stream, or when the discharge of a stream increases.
stream piracy
also known as stream capture, refers to the situation in which headward erosion causes one stream to intersect the course of another stream. The piracy of a stream that had been flowing through a water gap transforms the water gap into a wind gap, a dry pathway through a high ridge.
drainage reversal
plate tectonics changing the course of rivers.
superposed streams
a region in which drainage initially forms on a layer of soft, flat strata that uncomfortably overlies folded strata. Streams carve channels into the flat strata; when they eventually erode down through the unconformity and start to downcut into the folded strata. Geologists call such streams ___ ___, because their preexisting geometry has been laid down on the rock structure.
antecedent streams
in some cases, tectonic activity (such as subduction or collision) causes a mountain range to rise up beneath an already established stream. If the stream downcuts as fast as the range rises, it can maintain its course and will cut right across the range. Geologists call such streams ___ __, to emphasize that they existed before the range uplifted.
seasonal floods
floods that occur regularly when rainfall is particularly heavy or when winter snows start to melt are called ___ ___. Severe floods of this type take place in tropical regions that are drenched by monsoons.
flash floods
events during which the floodwaters rise so fast that it may be impossible to escape from the path of the water are called ___ ___. These happen during unusually intense rainfall or as a result of a dam collapse.
floodways
regions likely to be flooded, and then by moving or abandoning buildings located there.
annual probability
indicates the likelihood that a flood of a given size or larger will happen at a specified locality during any given year. For example, if we say that a flood of a given size has an annual probability of 1%, then we mean that there is a 1 in 100 chance that a flood of at least this size will happen in any given year.
recurrence interval
..of a flood of a given size is defined as the average number of years between successive floods of at least this size. For example, if a flood of a given size happens once in 100 years, on average, then it is assigned a recurrence interval of 100 years and is called 100-year-flood.
COAST
the region where the land meets the sea, and where over 60% of the global population lives today.
bathymetry
the variation in depth, based originally on sonar measurements and more recently on measurements made by satellites. Such studies indicate that the ocean contains broad bathymetric provinces, distinguished from each other by their water depth.
continental shelf
a relatively shallow portion of ocean in which water depth does not exceed 500 m, fringes the continent. Across the width of the shelf, the ocean floor slopes seaward at only about 0.3 degrees, an almost imperceptible amount.
abyssal plain
wide, flat area that makes up most of the ocean floor.
passive continental margins
broad continental shelves, like that of eastern North America, form along these, margins that are not plate boundaries and thus lack seismicity. They originate after rifting breaks a continent in two; when rifting stops and and sea-floor spreading begins, the stretched lithosphere at the boundary between the ocean and continent gradually cools and sinks.
active continental margins
a margin that coincides with a plate boundary and thus hosts many earthquakes, off South America. The edge of the Pacific Ocean is a convergent plate boundary, the narrow shelf along a convergent plate boundary forms where an apron of sediment spreads out over the top of an accretionary prism, the pile of material scraped off the downsloping subducting plate. Here, the continental slope corresponds to the face of the accretionary prism.
submarine canyons
at many locations, relatively narrow and deep valleys called ____ ___ dissect continental shelves and slopes.
pelagic sediment
as oceanic crust ages and moves away from the axis of the mid-ocean ridge, two changes take place. First the lithosphere cools, and as it does so, its surface sinks. Second, a blanket of ____ ___ gradually accumulates and covers the basalt of the oceanic crust. This blanket consists mostly of microscopic plankton shells and fine flakes of clay, which slowly fall like snow from the ocean water and settle on the sea floor. Because the ocean crust gets progressively older away from the ridge axis, sediment thickness increases away from the ridge axis.
seamount
with time, oceanic islands erode and partially collapse due to slumping. Also, the seafloor beneath them ages and sinks. As a result, each island's peak eventually submerges, and what was once an island becomes a ____.
guyot
A seamount that submerges after being overgrown by a reef will have a flat top, and can be called a ___. Oceanic islands and seamounts that developed above the same hot spot line up in a chain, with the oldest seamount at one end and the youngest seamount or island at the other.
salinity
changes with depth of the ocean. A graph of the variation in ___ content with depth indicates that such differences in this are found in seawater only down to a depth of about 1 km. Deeper waters tend to be more homogenous. Oceanographers refer to the gradational boundary between surface-water salinities and deep-water salinities at the halocline.
temperature
rises in the ocean markedly with depth. Waters warmed by the sun are less dense and tend to remain at the surface. An abrupt thermocline, below which water temperatures decrease sharply, reaching near freezing at the sea floor, appears at a depth of about 300 m, in the tropics. There is no pronounced thermocline in polar seas, since surface waters there are already so cold.
currents
oceanographic studies made since the Challenger expedition demonstrate that circulation in the sea occurs at two levels: surface ____ affect the upper hundred meters of water, and deep currents keep even water at the bottom of the sea in motion.
Coriolis effect
the movement of water resulting from wind shear does not exactly parallel the movement of the wind. This is a consequence of Earth's rotation, which generates the ____ __. This phenomenon causes surface currents in the Northern Hemisphere to veer toward the right and surface currents in the Southern Hemisphere to veer toward the left of the average wind direction.
gyres
because of the geometry of ocean basins and the pattern of wind directions, surface currents in the oceans today trace out large circular flow patterns known as __, clockwise in the northern seas and counterclockwise in the southern seas. North and South hemisphere __ merge at the equator, creating an equatorial westward flow.
downwelling
along coastal regions, these two phenomena exist because as the wind blows, it drags surface water along; If surface water moves toward the coast, then an oversupply of water develops along the shore and excess water must sink - that is, _____ occurs.
upwelling
along coastal regions, these two phenomena exist because as the wind blows, it drags surface water along; if surface water moves away from the coast, then a deficit of water develops near the coast and water rises to fill in the gap - ____ takes place. Takes place of subsurface water also occurs along the equator because the winds blow steadily from east to west.
thermohaline circulation
upwelling and downwelling can also be driven by contrasts in water density, caused by differences in temperature and salinity; we refer to the rising and sinking of water driven by density contrasts as ____ ____. During this process, denser water (cold and/or saltier) sinks, whereas water that is less dense (warm and/or less salty) rises.
tide
the rise and fall of sea level, a vertical movement called a __. The tidal reach, meaning the difference between sea level at high tide and sea level at low tide, depends on location. The intertidal zone, the region submerged at high tide and exposed at low tide, is a fascinating ecological niche.
tide-generating force
tides are caused by this force, which is due in part to the gravitational attraction of the Sun and Moon and in part by the centrifugal force caused by the revolution of the Earth-Moon system around its center of mass.
tilt of Earth's axis
factors affecting the timing and magnitude of tides; because the spin axis of the Earth is not perpendicular to the plane of the Earth-Moon system, a given point passes between a high part of one bulge during one part of the day, and through a lower part of the other bulge during another part of the day, so the two high tides at the given point are not the same size.
the Moon's orbit
factors affecting the timing and magnitude of tides; the moon progresses in its 28-day orbit around the Earth in the same direction as the Earth rotates. High tides arrive 50 minutes later each day because of the difference between the time it takes for Earth to spin on its axis, and the time it takes for the Moon to orbit the Earth.
the Sun's gravity
factors affecting the timing and magnitude of tides; when the angle between the direction to the Moon and the direction to the sun is 90 degrees, we experience extra-low tides (neap tides) because the Sun's gravitational attraction counteracts the Moon's. When the Sun is on the same side as the Moon, we experience extra-high tides (spring tides) because the Sun's attraction adds to the Moon's.
focusing effect (of bays)
factors affecting the timing and magnitude of tides; in the open ocean, the maximum tidal reach is only a few meters. But in the Bay of Fundy, along the eastern coast of Canada, the tidal reach approaches 20 m. In a bay that narrows to a point, such as the Bay of Fundy, the flood tide brings a large volume of water into a small area, so the point experiences an especially large high tide.
basin shape
factors affecting the timing and magnitude of tides; the shape of the basin containing a portion of the sea influences the sloshing of water back and forth within the basin as tides rise and fall. Depending on the timing and magnitude of this sloshing, this effect can locally add to the global tidal bulge or subtract from it, and thus can affect the rhythm of tides. In some locations, the net effect is to cancel is to cancel one of the daily tides entirely, so that the locality experiences only one high tide and one low tide in a day.
air pressure
factors affecting the timing and magnitude of tides; the effects of air pressure on tides can contribute to disaster. For example, during a hurricane the air pressure drops radically, so the sea surface rises; if the hurricane coincides with a high tide, the storm surge (water driven landward by the wind) can inundate the coast.
wave base
Depth below the wave crest at which water movement associated with the wave becomes negligible; about half the wave length.
rogue waves
wave interference, the interaction of wind-driven waves with strong currents, and focusing due to the shape of the coastline or sea floor can lead to the formation of ___ ___, defined as waves that are more than twice the size of most large waves passing a locality during a specified time interval.
swash
waves affect the shoreline, where the wave base just touches the floor it causes a slight back-and-forth motion of sediment. Closer to shore, as the water gets shallower, friction between the wave and the motion in the wave becomes more elliptical. Eventually, water at the top of the wave curves over the base, and the wave becomes a breaker. Breakers crash onto the shore in the surf zone, sending a surge of water up the beach. This upward surge, or ___, continues until friction brings motion to a halt. Then gravity draws the water back down the beach as 'backwash'
wave refraction
waves may make a large angel with the shoreline as they're coming in, but they bend as they approach the shore, a phenomenon called __ ____; right at the shore, their crests make no more than about a 5 degree angle with the shoreline.
longshore current
though refraction decreases the angle at which a wave rolls onto shore, the wave may still arrive at an angle. When the water returns seaward in the backwash, however it must flow straight down the slope of the beach in response to gravity. Overall, this sawtooth-like flow results in a ___ __.
beach
a gently sloping fringe of sediment along the shore. Some beaches consist of pebbles or boulders, whereas others consist of sand grains. Waves winnow out finer sediment like silt and mud and carry it to quieter water, where it settles. Sands derived from the weathering and erosion of silicic-to-intermediate rocks consist of mainly of quartz; other minerals in these rocks chemically weather to form clay, which washes away in waves. Those made from the erosion of limestone or of recent corals and shell beds consist of carbonate sand, including masses of sand-sized chips of shell.
beach face
a beach profile, a cross section drawn perpendicular to the shore, illustrates the shape of a beach. Starting from the sea and moving landward, a beach consists of a foreshore zone, or intertidal zone, across which the tide rises and falls. The ___ ___, is a steeper, concave part of the foreshore zone, and forms where the swash of the waves actively scours the sand.
berms
on a beach cross section, the backshore zone extends from a small step, or escarpment, cut by high-tide swash to the front of the dunes or cliffs that lie farther inshore. The backshore zone includes one or more ___, horizontal to landward-sloping terraces that received sediment during a storm.
beach drift
where waves hit the beach at an angle, the swash of each successive wave moves active sand up the beach at an angle to the shoreline, but the backwash moves this sand down the beach parallel to the slope of the shore. This sawtooth motion causes sand gradually to migrate along the beaches, a process called ___ ___. This happens in association with the longshore drift of water, can transport sand hundreds of kilometers along a coast in a matter of centuries.
sandspit
where the coastline indents landward, beach drift stretches beaches out into open water to create a ____. Some of these can grow across the opening of a bay, to form a baymouth bar.
barrier islands
in regions with an abundant sand supply, offshore bars rise above the mean high-water level and become ___ ___. The water between one of these and the mainland becomes a quiet water lagoon, a body of shallow seawater separated from the open ocean.
bioturbation
tidal flats are regions of mud and silt exposed or nearly exposed at low tide but totally submerged at high tide, develop in regions protected from strong wave action. They are typically found along the margins of lagoons or on shores protected by barrier islands. Here, mud and silt accumulate to form thick, sticky layers. In tidal flats that provide a home for burrowing organisms such as clams and worms, ____ ("stirring by life") mixes sediments together.
wave-cut notch
lacking the protection of a beach, rocky coasts feel the full impact of ocean breakers. The water pressure generated during the impact of a breaker can pick up boulders and smash them together until they shatter, and it can squeeze air into cracks, creating enough force to widen them. Further because of its turbulence, the water hitting a cliff face carries suspended sand, and thus can abrade the cliff. The combined effects of shattering, wedging, and abrading together called wave erosion, gradually undercut a cliff face and make a ___ ___.
wave-cut bench
after a wave-cut notch is formed on a cliff face, undercutting continues until the overhang becomes unstable and breaks away at a joint, creating a pile of rubble at the base of the cliff that waves immediately attack and break up. In this process, wave erosion cuts away at a rocky coast, so that the cliff gradually migrates inland. Such cliff retreat leaves behind a ___ ___, or platform, which becomes visible at low tide.
coastal wetland
the gentlest type of shore; a vegetated, flatlying stretch of coast that floods with shallow water but does not feel the impact of strong waves. In temperate climates, coastal wetlands include swamps, marshes, and bogs. So many marine species spawn in wetlands that despite their relatively small area when compared with the oceans as a whole, these account for 10 to 30% of marine organic productivity.
estuaries
along some coastlines, a relative rise in sea level causes the sea to flood river valleys that merge with the coast, resulting in ____, where seawater and river water mix. You can recognize one of these on map by the dendritic pattern of its river-carved coastline.
fjords
the water stored in glaciers, along with the water within the vast ice sheets that covered continents during the ice age, flowed back into the sea and caused sea level to rise. The rising sea filled the deep valleys, creating ___, or flooded glacial valleys.
coral reef
the realm of shallow water underlain by coral mounds, associated organisms, and debris comprises a ___ ___. These absorb wave energy and thus serve as a living buffer zone that protects coasts from erosion. They need clear, well-lit, warm (18-30 C) water with normal oceanic salinity, so they only grow along clean coasts at latitudes of less than about 30 degrees. Three categories on the basis of their geometry: fringing reefs, barrier reefs, and atolls.
coastal plain
along a passive tectonic margin, the cooling and sinking of the lithosphere may create a broad ___ ___, a flatland that merges with the continental shelf, as exists along the Gulf Coast and southeastern Atlantic coast of the United States.
eustatic sea-level changes
some relative sea-level changes are due to a global rise or fall of the ocean surface. Such ____ ____ ____ may reflect changes in the volume of mid-ocean ridges, for example, displaces water and causes sea level to rise. These may also reflect changes in the volume of glaciers, for glaciers store water on land.
emergent coasts
geologists refer to coasts where land is rising or rose relative to sea level as ___ ___. At these, steep slopes typically border the shore. A series of step-like terraces form along some, these terraces reflect episodic changes in relative sea level.
submergent coasts
those coasts at which the land sinks relative to sea level become ____ ___. At these, landforms include estuaries and fjords that developed when the sea flooded coastal valleys. Many of the coastal landforms of eastern North America are the consequences of submergence.
beach nourishment
in some places, people have given up trying to decrease the rate of beach erosion, and instead have worked to increase the rate of sediment supply. To do this, they truck or ship in vast quantities of sand to replenish a beach. This procedure can be hugely expensive and at best provides only a temporary fix, for the backwash and beach drift that removed the sand in the first place continue unabated as long as the wind blows and the waves break.
organic coasts
coasts in which living organisms control landforms along the shore are called ___ ___. These coasts, a manifestation of interaction between the physical and biological components of the Earth System, are particularly susceptible to changes in the environment. The loss of such landforms can increase a coast's vulnerability to erosion and, because they provide spawning grounds for marine organisms, can upset the food chain of the global ocean.
HYDROGEOLOGY
a large proportion of professional geologists specialize in this field of geology, spending their careers either identifying usable sources of subsurface water or proposing strategies to clean contaminated supplies. For millennia, subsurface freshwater (which accounts for about 30% of the freshwater on Earth) has been a major resource for homes, farms, and industry, so knowledge of this water has practical value.
primary porosity
porosity formed during sediment deposition and during rock formation. It includes the pores between clastic grains that exist because the grains don't fit together tightly during deposition. Such pores survive the process of lithification if cementation is incomplete.
secondary porosity
porosity referring to the new pore space in rocks, produced some time after the rock first formed. For example, when rocks fracture, the opposing walls of the fracture do not fit together tightly, so narrow spaces remain in between. Thus, joints and faults may provide these for water.
factors of permeability
the permeability of a material depends on several factors: number of available conduits, size of the conduits, and the straightness of the conduits. for groundwater to flow, pores must be linked by conduits (openings). The ability of a material to allow fluids to pass through an interconnected network of pores is a characteristic known as ____. Water flows easily through a permeable material; in contrast, water flows slowly or not at all through an impermeable material.
aquifers
sediment or rocks that transmit water easily; Those that intersect the surface of the Earth are called unconfined, because water can percolate directly from the surface down into it and water from it can rise to the surface. Those that are separated from the surface are called confined.
aquitards
sediment or rocks that do not transmit water easily and therefore retard the motion of water.
unsaturated zone
category of underground water; infiltrating water can enter permeable sediment and bedrock by percolating along cracks and through conduits connecting pores. Nearer the ground surface, water only partially fills pores, leaving some space that remains filled with air. The region of the subsurface in which water only partially fills pores is called the ____ ___, or the vadose zone; the water that resides in this region is vadose-zone water.
saturated water
category of underground water; deeper down, water completely fills, or saturates, the pores. This region is the ____ ___, or the phreatic zone. Geologists use the term 'groundwater' specifically for subsurface water in the saturated zone, where water completely fills pores.
water table
refers to the horizon that separates the unsaturated zone above from the saturated zone below. Material above the ___ ___ can be damp, but pores are not full. Typically, surface tension, the electrostatic attraction of water molecules to mineral surfaces, causes water to seep up from the this region, filling pores in the capillary zone, a thin layer at the base of the unsaturated zone.
water table topography
the water table lies at a higher elevation beneath hills than it does beneath valleys. The relief (the vertical distance between the highest and lowest elevations) of the water table is not as great as that of the overlying land, so the surface of the water table lends to be smoother than that of the landscape. The elevation of the water table varies because groundwater moves so slowly through rock and sediment that it cannot quickly assume a horizontal surface.
perched water table
in some locations, layers of strata are discontinuous, meaning that they pinch out at their sides. As a result, lenshaped layers of impermeable rock (such as shale) may lie within a thick aquifer. A mound of groundwater accumulates above this aquitard. The result is a ___ ___ ___, a quantity of groundwater that lies above the regional water table because an underlying lens of impermeable rock or sediment prevents the water from sinking down to the regional water table.
hydraulic head
the potential energy available to drive the flow of a given volume of groundwater at a location is called the ___ __. To measure this at a point in an aquifer, hydrogeologists drill a vertical hole down to the point and then insert a pipe in the hole. The height above a reference elevation (sea level) to which water rises in the pipe represents this head. As a rule, groundwater flows from regions where this is higher to regions where this is lower.
recharge area and discharge area
the location where water enters the ground (where the flow direction has a downward trajectory) is called the ___ ___, and the location where groundwater flows back up to the surface is called the ___ ___.
groundwater flow rate
ranges between 0.01 and 1.4 m per day (about 4-500 m per year). Groundwater moves by percolating through a complex, crooked network of tiny conduits; it must travel a much greater distance than it would if it could follow a straight path. Also, friction and/or electrostatic attraction between groundwater and conduit walls slows down the water flow.
hydraulic gradient
the rate at which groundwater flows at a given location depends on the permeability of the material containing the groundwater; groundwater flows faster in material with greater permeability than in less permeable material. Rate also depends on the ____ ____, the change in hydraulic head per unit of distance between two locations as measured along the flow path. If there is a large difference in the hydraulic head over a given distance, then a greater amount of energy drives the flow, so the flow is faster.
Darcy's Law
law that states that groundwater flows faster through very permeable rocks than through impermeable rocks, and that it flows faster where the water table has a steep slope than where the water table has a shallow slope.
wells
___ are holes that people dig or drill to obtain water. And ___ springs are natural outlets from which groundwater flows. Both provide welcome sources of water but must be treated with care if they are to last.
ordinary well
type of well; the base of the well penetrates an aquifer below the water table. Water from the pore space in the aquifer seeps into the well and fills it; the water surface in the well is the water table, some of these wells are seasonal and require a rainy season in order to provide.
cone of depression
if an ordinary well-user pumps water to quickly, then the water table sinks down around the well, a process called drawdown, so that the water table becomes a downward-pointing, cone-shaped surface called..
artesian well
type of well; penetrates confined aquifers, in which water is under enough pressure to rise on its own to a level above the surface of an aquifer. If this level lies below the ground surface, the well is a nonflowing ___ well. But if the level lies above the ground surface, the well is a flowing ___ well, and water actively fountains out of the ground. These types of wells occur in special situations where a confined aquifer lies beneath a sloping aquitard.
spring-forming conditions
springs form under a variety of conditions: (1) where the ground surface intersects the water table in a discharge area, valley floors adding water to lakes or streams; (2) where downward-percolating water runs into an impermeable layer and migrates along the top surface of the layer to a hillslope; (3) where a particularly permeable layer or zone intersects the surface of a hill, water percolates down through the hill and then migrates along the permeable layer to the hill face; (4) where a network of interconnected fractures channels groundwater to the surface of a hill; (5) where flowing groundwater collides with a steep impermeable barrier.
artesian springs
type of spring forming if the ground surface intersects a natural fracture (joint) that taps a confined aquifer in which the pressure is sufficient to drive the water to the surface.
hot springs
springs that emit water ranging in temperature from about 30 degrees C to 104 C, they are found in two geologic settings: they occur where very deep groundwater, heated in warm bedrock at depth, flows up to the ground surface. This water brings heat with it as it rises. Such springs form in places where faults or fractures provide a high-permeability conduit for deep water, or where the water emitted in a discharge region followed a trajectory that first carried it deep into the crust.
geothermal regions
hot springs develop in these regions, places where volcanism currently takes place or has occurred recently, so that magma and/or very hot rock resides close to the Earth's surface. In hot springs, groundwater dissolves minerals from rock that is passes through. Hot groundwater contains more dissolved minerals because water becomes a more effective solvent when hot. People use the water emitted at hot springs to fill relaxing mineral baths.
geyser
resulting from a geothermal waters, a fountain of steam and hot water that erupts episodically from a vent in the ground. Beneath this formation lies a network of irregular fractures in very hot rock; groundwater sinks and fills these fractures. Adjacent hot rock then superheats the water: it raises the temperture above the temperature at which water at a pressure of 1 atm will boil. Eventually, the superhot water rises through a conduit to the surface. When some of this water transforms into steam, the resulting expansion causes water higher up to spill out of the conduit at the ground surface.
groundwater depletion
a number of problems accompany the depletion of groundwater, which is essentially a non-renewable resource: (1) lowering of the water table; (2) reversing the flow direction of groundwater; (3) saline intrusion; (4) pore collapse and land subsidence. To avoid such problems, communities have sought to prevent groundwater depletion either by directing surface water into recharge areas, or by pumping surface water back into the ground.
hard water
groundwater that has passed through limestone and dolomite contains dissolved calcium and magnesium ions; this water, called __ __, can be a problem because carbonate minerals precipitate from it to form "scale" that clogs pipes, difficult to wash with, can contain toxic arsenic or hydrogen sulfide.
groundwater contamination
the addition of such substances in quantities that make the groundwater dangerous to use is ____ ____; contaminants have increasingly been introduced into aquifers through human activity, including: agricultural waste, industrial waste, effluent from landfills and septic tanks, petroleum products, radioactive waste, and acids leached from sulfide minerals in coal and metal mines.
contaminant plume
the cloud of contaminated groundwater that moves away from the source of contamination is called a ____ ___. Staggering quantities of contaminating liquids (trillions of gallons in the US alone) enter the groundwater system every year.
bio-remediation
the process of injecting oxygen and nutrients into a contaminated aquifer to foster growth of bacteria that can react with and break down molecules of contaminants.
speleothems
rock formed within caves by calcium carbonate precipitation is a type of travertine called dripstone, and the various intricately shaped formations that grow in caves by the accumulation of dripstone are called ____.
stalactites and stalagmites
where water drips from the ceiling of a cave, the precipitated limestone adds to the tip of an icicle-like cone called a ____. Where the drip hits the floor, resulting precipitate builds an upward-pointing cone called a ____. If the process of dripstone formation in a cave continues long enough, these structures merge to create limestone columns.
natural bridge and disappearing streams
where most of a cave collapsed, a ___ ___ spans the cave remnant. Where the water table rises above the floor of a sinkhole, the sinkhole fills to become a lake. Where surface streams intersect cracks or holes than link to the caves below, the water disappears into the subsurface and becomes an underground stream. Such ____ ___ reemerge from a cave entrance downstream.
karst landscapes
geologists refer to landscapes such as the Kras Plateau in which surface features reflect the dissolution of bedrock below as ___ ____. Form in a series of stages: (1) establishment of water table in limestone; (2) formation of cave network; (3) drop in the water table; (4) roof collapse.
METAMORPHIC ROCK
a rock that forms from a preexisting rock, that undergoes mineralogical and textural changes in response to modification of its physical or chemical environment.
Protolith
the parent rock of metamorphism. Is subjected to heat, pressure, differential stress, and/or hydrothermal fluids. The mineral makeup of the parent will determine the degree to which each metamorphic agent will cause change.
Metamorphism
the process of forming metamorphic rock, new minerals may grow at the expense of old ones, and/or size, shape, and arrangement of grains in the rock may change; a solid-state process.
Metamorphic texture
the nature of metamorphic rocks in which ways the grains in the rock have grown in place and interlock; slate, phyllite, schist, gneiss.
Metamorphic minerals
new minerals that only grow under metamorphic temperatures and pressures - metamorphism can produce a group of minerals called a metamorphic mineral assemblage.
Recrystallization
metamorphic formation process; changes the size/shape of the grains without changing the identity of the mineral constituting the grains.
Phase change
metamorphic formation process; transforms a grain of one mineral into a grain of another mineral with the same composition but a different crystal structure. At an atomic scale, phase change involves rearrangement of atoms.
neocrystallization (or metamorphic reaction)
metamorphic formation process; results in the growth of new mineral crystals that differ from those of the protolith. During this process, one or more chemical reactions digest (reactants) minerals of the protolith to produce new minerals (products) of the metamorphic rock. For this process to take place, atoms must migrate, or diffuse, through solid crystals, a very slow process, and/or dissolve and reprecipitate at grain boundaries, with the aid of hydrothermal fluids sometimes.
Pressure solution
metamorphic formation process; happens when a rock is squeezed more strongly in one direction that in others at relatively low pressures and temperatures, in the presence of water. Mineral grains dissolve where their surfaces are pressed against other grains, producing ions that migrate through the water to precipitate elsewhere.
Plastic deformation
metamorphic formation process; happens at elevated temperatures and pressures, conditions that permit some minerals to behave like soft plastic, that if they are stretched or squeezed, they become flattened or elongate without breaking.
Metamorphism due to heating
heating causes atoms to vibrate, chemical bonds to detach and rearrange, as a consequence recrystallization and/or neocrystallization take place. These processes enable a metamorphic rock assemblage to grow in solid rock. Sources: contact metamorphism and increased depth. Temperatures between 200 and 850 deg C.
Metamorphism due to pressure
when minerals are subjected to extreme pressure, denser minerals tend to form. Such transformations involve phase changes and/or neocrystallization. Rocks subjected to ultra-high pressure contain grains of coesite, a phase of SiO2 that is much denser than familiar quartz.
Metamorphism to due pressure+temperature
In the Earth, pressure and temperature change together with increasing depth. At a depth of 8km, temperature in rock is about 200C and pressure is about 2.3 kbar. A depth of 20km yields temperature and pressure of 500C and 5.5 kbar respectively.
Differential stress
when a metamorphic material is squeezed or stretched unequally from different sides. Under these conditions, the push or pull in one direction differs in magnitude from the push or pull in another direciton.
Normal stress
type of differential stress; when material is pushed or pulled perpendicular to a surface. A push is called a compression (flattens) and a pull, tension (stretches).
Shear stress
type of differential stress; one part of the material is moved sideways, relative to another.
Preferred mineral orientation
as a rock changes shape under elevated temperatures and pressures, the internal texture of the rock also changes, typically resulting in this type of development. In wet rocks low temperatures, pressure solution dissolves on the faces perpendicular to the direction of compression. At high temperatures, grains flatten in response to differential stress by means of plastic deformation. And grain growth (neocrystallization) may produce preferred orientation, because certain minerals grow faster in the direction in which a rock is stretching than in other directions.
Hydrothermal fluids
metamorphic reactions usually take place in the presence of these, because water occurs throughout the crust. Referred to as "hot water solutions", can include hot water, steam, and supercritical fluid. These fluids are chemically active, in that they are able to react chemically with rock; can dissolve certain minerals and enhance ion migration, thus they are present as solutions and not just water.
Role of hydrothermal fluids
these fluids accelerate metamorphic reactions, for atoms involved in the reactions can migrate faster through a fluid than they can through a solid. Fluids provide water that can be absorbed during metamorphic reactions. And when passing through a rock, a fluid may pick up some dissolved ions and drop off others, thus changing the whole composition of a rock during metamorphism.
Metasomatism
the process by which a rock's chemical composition changes because of a reaction with hydrothermal fluids. Dissolved ions carried away by hydrothermal fluids either react with rocks elsewhere, reach the Earth's surface and wash away, or precipitate to form veins.
Vein
a mineral filled crack that cuts across preexisting rock.
Metamorphic foliation
refers to the repetitions of planar surfaces or layers in a metamorphic rock. Can give a metamorphic rock a striped or streaked appearance in an outcrop, and/or give them the ability to split into thin sheets.
Slate
metamorphic texture; the finest-grained foliated metamorphic rock, consists of slaty cleavage. Forms in response to differential stress, typically, cleavage planes form perpendicular to the direction of compression.
Phyllite
metamorphic texture; a fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained white mica and chlorite. Forms by the metamorphism of slate at a temperature high enough to cause neocrystallization; metamorphic reactions produce a new assemblage of minerals out of clay.
Schist
metamorphic texture; a medium/coarse-grained metamorphic rock that possesses a type of foliation, defined by the preferred orientation of large mica.
Gneiss
metamorphic texture; compositionally layered metamorphic rock, typically composed of alternating dark-colored and light-colored layers or lenses that range in thickness.
Migmatite
At very high temperatures, or if hydrothermal fluids enter the rock and lower its melting temperature, gneiss begins to partially melt, producing magma that is enriched in silica. In some cases, this melt does not move very far before freezing to form a light-colored igneous (felsic) rock. The resulting mixture of igneous and relict metamorphic rock is this type of rock.
Hornfels
nonfoliated metamorphic rock; a rock that undergoes metamorphism because of heating in the absence of differential stress. The crystals grow in random orientations, prevents foliation.
Amphibolite
nonfoliated metamorphic rock; metamorphism of mafic rocks (basalt and gabbro) can't produce quartz and muscovite when metamorphosed, for these rocks don't contain the right mix of chemicals to yield such minerals. They transform into this dark-colored rock containing hornblende and plagioclase.
Quartzite
nonfoliated metamorphic rock; during metamorphism, preexisting quartz grains recrystallize, creating new, larger grains. Forms from quartz sandstone.
Marble
nonfoliated metamorphic rock; the metamorphism of limestone, calcite composing the protolith recrystallizes; as a consequence original sedimentary features become hard to recognize, pore space disappears, and the distinction between grains and cement disappears.
Metamorphic grade
the term used to indicate the intensity of metamorphism, the amount or degree of metamorphic change within a rock. Depends primarily on temperature, plays the dominant role in determining the extent of recrystallization/neocrystallization during metamorphism. Low to high grade: shale, slate, phyllite, schist, gneiss, migmatite.
Metamorphic zones
the regions between two isograds (the line on a map along which an index mineral first appeared); zones are named after an index mineral that was not present in the previous, lower-grade zone.
Metamorphic aureole
the distinct belt of metamorphic rocks that forms around an igneous intrusion, also known as a contact aureole. Because this metamorphism takes place without application of differential stress, aureoles contain hornfels, a nonfoliated metamorphic rock.
Thermal metamorphism
the local metamorphism caused by an igneous intrusion; develops in response to heat without a change in pressure and without differential stress.
Contact metamorphism
the local metamorphism caused by an igneous intrusion; develops adjacent to an intrusion. Occurs anywhere that the intrusion of plutons occurs. Plutons intrude into the crust at convergent plate boundaries, in rifts, and during mountain building that takes place when continents collide.
Burial metamorphism
metamorphism due only to the consequences of very deep burial; causes the organic molecules of oil to break up and for this reason, oil drillers stop drilling when the bottom of the hole reaches depths at which this metamorphism has begun.
Dynamic metamorphism
Near the Earth's surface, the movement of faults sliding past each other breaks fracture rock into angular fragments, or crush into powder. But at greater depths rock is so warm that it behaves like soft plastic as shear along the fault takes place, during this process the minerals in the rock crystallize. It occurs as a consequence of shearing along, under metamorphic conditions, without requiring a change in temperature or pressure.
Mylonite
the resulting rock from dynamic metamorphism; has a foliation that parallels the fault.
Dynamothermal metamorphism
foliated rock metamorphism; as a consequence of developing mountain ranges, large slices of continental crust slip up and over portions of the crust, the resulting rock that was once near the Earth's surface along the margin of the continent ends up at depth beneath the mountain range. In this new environment, 3 changes occur: the protolith heats up due to the geothermal gradient and igneous activity, the protolith is subjected to greater pressure due to overburden, and the protolith undergoes squashing and shearing because of differential stress generated by plate interaction.
Regional metamorphism
dynamothermal metamorphism affecting a large region. Metamorphism involving heat but also shearing and squashing. Produces the greatest quantity of metamorphic rock, associated with mountain building.
Hydrothermal metamorphism
type of metamorphism; hot magma rises beneath the axis of the mid-ocean ridges, so when cold seawater sinks through cracks down into the oceanic crust along ridges; it heats up and transforms into hydrothermal fluid. Metamorphoses ocean-floor basalt; produces chlorite, greenish hue.
Blueschist
a relatively rare metamorphic rock that contains an unsual blue-colored amphibole called glaucophane. Occurs only in the accretionary prisms that form at subduction zones. Because of shear between the subducting plate and the overriding plate, foliation develops.
Shock metamorphism
When large meteorites slam into the Earth, a vast amount of kinetic energy transforms into heat and a pulse of extreme compression (a shockwave) propagates the Earth. The heat may be sufficient to melt or even vaporize rock at the impact site, and the extreme compression of the shock waves causes the crystal structure of quartz grains in rocks below the impact site to suddenly undergo a phase change to a more compact mineral called coesite.
Exhumation
process by which overlying rock is removed and deeper rock rises, these rocks are exposed as towering cliffs of gneiss and schist. The overall process by which deeply buried rocks end up back at the surface, occurs relatively quickly.
Shield
huge expanses of metamorphic rock crop out in older portions of a continent, where extensive areas of Precambrian rock crop out at the ground surface because overlying younger rock has eroded away.
GEOLOGIC TIME
the span of time since Earth's formation.
Principle of uniformitarianism
James Hutton's, the father of geology, principle theory, states that physical processes we observe today also operate in the past and were responsible for the formation of the geologic features we see in outcrops. The present is the key to the past.
relative age
the age of one feature with respect to another
numerical age
age of a feature given in years
principle of superposition
sequence of sedimentary rock layers, each layer must be younger than the one below, for a layer of sediment cannot accumulate unless there is already a substrate on which it can collect. Thus, the layer at the bottom of a sequence is the oldest, and the layer at the top is the youngest. (Nicolaus Steno)
principle of original horizontality
sediments on Earth settle out of a fluid in a gravitational field. Typically, the surfaces on which sediments accumulate are fairly horizontal (such as a floodplain or the bed of a lake or sea), if sediments were deposited on a steep slope, they would slide down before being lithified into a layer. Therefore, when layers of sediment are originally deposited, they are fairly horizontal.
principle of original continuity
sediments generally accumulate in continuous sheets. If today you find a sedimentary layer cut by a canyon, then you can assume that the layer once spanned the canyon but was later eroded by the river that formed the canyon.
principle of cross-cutting relations
if one geologic feature cuts across another, the feature that has been cut is older. For example, if an igneous dike cuts across a sequence of sedimentary beds, the beds must be older than the dike.
the principle of inclusions
if an igneous intrusion contains fragments of another rock, the fragments must be older than the intrusion. If a layer of sediment deposited on an igneous layer includes pebbles of the igneous rock, then the sedimentary layer must be younger. The fragments (xenoliths) in an igneous body and the pebbles in the sedimentary layer are inclusions, or pieces of one material incorporated in another. The rock containing the inclusion must be younger than the inclusion.
principle of baked or chilled contacts
an igneous intrusion metamorphoses surrounding rocks. The rock that has been 'baked' must be older than the intrusion. Similarly, since an intrusion injects into cooler rocks, the margin of the intrusion cools rapidly and its finer grained than the interior.
geologic history
a definition of the relative ages of events that took place in a certain region. Begin by noting the kinds of rocks and structures present, and then you look at the relationships between the igneous rocks and the sedimentary rocks. And lastly, you consider the fault and the land surface.
fossil assemblage
the group of fossil species. Can occur only in a limited interval of strata, not above or below certain levels.
principle of fossil succession
the predictability of fossil distribution, which allows geologists to arrange fossil species in a progression from older at the bottom to younger at the top, has been found at countless locations around the world.
range
interval in the sequence in which fossils occur. The sequence contains a definable succession of fossils that the range in which a particular species occurs overlaps with the range of other species, and that once a species vanishes, it does not reappear higher in the sequence.
unconformity
a surface, representing a period of non deposition and possibly erosion. The interval of time between deposition of the youngest rock below the uncomformity and deposition of the oldest rock above is called a hiatus. Essentially this type of structure occurs wherever the land surface does not receive and accumulate sediment.
angular unconformity
type of unconformity; tilted rocks are overlain by flat-lying rocks; rocks below an unconformity that were tilted or folded before the unconformity developed by faulting and then being uplifted and eroded. Cuts across the underlying layers; layers below have different orientation from the layers above.
nonconformity
type of unconformity; older metamorphic or intrusive igneous rocks in contact with younger sedimentary strata; type of unconformity at which sedimentary rocks overlie intrusive igneous rocks and/or metamorphic rocks. The igneous or metamorphic rocks must have cooled, been uplifted, and been exposed by erosion to form the substrate on which new sedimentary rocks were deposited. Here, you typically will find pebbles of the igneous or metamorphic in the lowest bed of the sedimentary sequence.
disconformity
type of unconformity; strata on either side are parallel; an unconformity parallel to the two sedimentary sequences it separates. Sediment deposited beneath a shallow sea, the deposited beds become exposed when sea level drops and during this time, no new sediment accumulates, and some of the preexisting sediment gets eroded away. Even though the beds above and below this type of unconformity are parallel, the contact between them represents an interruption in deposition.
stratigraphic column
used to summarize info about the sequence of strata at a location. Typically, these columns are drawn to scale, so that the relative thickness of layers portrayed on the column represent the thicknesses of layers in the outcrop.
stratigraphic formation
'formations' within a stratigraphic column; recognizable intervals of a specific rock type or group of rock types deposited during a specific time interval, that can be traced over a fairly broad region
contact
boundary surface between two stratigraphic formations is a type of geologic...
correlation
age relationship between the strata at one locality and the strata of another. 'Lithographic' and 'method fossil' variations; nearby and broad relationships respectively.
geologic map
portrays the spatial distribution of rock units at the earths surface. Formed through correlated strata at many locations, allows you to trace individual formations of strata over fairly broad regions.
geologic column
a composite stratigraphic column; represents a specific interval of time. The largest subdivisions break Earth history into the Hadean, Archean, Proterozoic, and Phanerozoic Eons.
eras
subdivision of an eon - from oldest to youngest they are Paleozoic, Mesozoic, Cenozoic.
periods; epochs
from geologic eras, we can further divide each era into____and each of of these into_____
Cambrian explosion
the remarkable diversification of life, indicated by the fossil record, that occurred at the beginning of the Cambrian Period.
Eons
the largest subdivision of geologic time.
Precambrian
Interval of geologic time between Earth's formation about 4.57 Ga and the beginning of the Phanerozoic Eon 542 Ma
radioactive decay
process by which a radioactive atom undergoes fission or releases particles thereby transforming into a new element. All these reactions change the atomic number of the nucleus and thus form a different element.
half-life
the time measured of how long it takes for half a group of isotopes to decay. We cannot predict which specific isotopes decay at which time, only that during a half-life, half the parent isotopes decay to form daughter isotopes. For a given reaction, the half life is a constant.
closure temperature
the temperature below which isotopes are no longer free to move. This temperature level is typically significantly cooler than the melting temperature of a mineral. When we specify a radiometric date for a rock, we are defining the time at which a specific mineral in the rock cooled below its ___ temperature.
growth rings
consequence of seasonal changes; develop in trees, travertine deposits, and shelly organisms
rhythmic layering
layering that develops in sedimentary accumulations and glacier ice
magnetostratigraphy
Geologists having determined when magnetic reversals took place, have constructed a reference column showing the succession of reversals through time. By comparing the pattern of the reversals in a sequence of strata with the bar code of the reference column, scientists can determine the age of the sequence.
fission tracks
the ejection of an atomic particle during the decay of a radioactive isotope damages the nearby crystal lattice, creating a line called a...; as time passes, more atoms undergo fission, so the number of fission ___ in the crystal increases.
geologic time scale
scale that describes the intervals of geologic time. Dinosaurs appeared during the Triassic period, between 251 and 250 million years ago.
Cenozoic
The most recent era of the Phanerozoic Eon, lasting from 65 Ma up until present
Paleozoic
Oldest era of the Phanerozoic Eon
Mesozoic
The middle of the three Phanerozoic eras; lasted from 245 Ma to 65 Ma
COSMOLOGY
the study of the overall structure and evolution of the Universe.
Universe
the workings of ourselves and all that surrounds us, our..
geocentric model
Universe structure theory in which the Earth sits motionless at the center of the Universe while the Sun and all planets follow perfectly circular orbits around it.
light year
the distance that light travels in one Earth year, equals about 9.5 trillion km. Galaxies at the outer edge of the Universe lie over 13 billion light years away (78 trillion miles away). Light traveling to Earth from such locations began their journey 9 billion years ago before the Earth even existed.
galaxies
stars are not randomly scattered throughout the Universe; gravity pulls them together to form immense systems, or groups called...
the Doppler effect
a change in the frequency of waves caused by a moving source, or a moving observer. 1.) Change in λ or frequency of a wave due to the source either approaching you or receding from you (works with sound and EMR) 2.) Blue Shift-towards you, Red Shift-away from you 3.) Used to detect motion, direction, and speed of stars
expanding Universe theory
Edwin Hubble realized that the light from all distant galaxies, regardless of their direction from Earth, exhibits a red shift, all distant galaxies are moving rapidly away from us. No longer could we view the Universe as being fixed in dimension, with galaxies locked in position, Universe expansion was occurring.
big bang
(cosmology) the cosmic explosion that is hypothesized to have marked the origin of the universe. All matter and energy - everything that now constitutes the Universe - was initially packed into an infinitesimally small point. For reasons that no one fully understands, the point exploded about 13.7 billion years ago.
Nebulae
as the Universe continued to expand and cool further, following the big bang, atoms and molecules slowed down and accumulated into these patchy clouds of gas.
accretion disk
in the young Universe, the gravitational pull of an initially denser region of nebula began to pull in surrounding gases and grew in mass and density. Because of rotation, the condensing portion of the nebula evolved into a spinning disk-shaped mass of gas...
protostar
Early form of a star; This stage lies between the collapsing of dust and gas and the beginning of nuclear fusion. The central ball of an accretion disk becomes hot enough to glow, due to kinetic energy and thermal energy.
supernova
a star that explodes and becomes extremely luminous in the process.
stellar wind
the stream of atoms emitted from a star during its lifetime; particles that have been ejected from a star and are shooting through space
planet
a large, spherical solid object orbiting a star, and may itself travel with a moon or many moons.
moon
is an object locked in orbit around a planet; all but two of the planets have them.
terrestrial planets
type of planet that consists of a shell of rock surrounding a core of iron alloy; the inner planets (Mercury, Venus, Earth, Mars).
gas-giant planets
type of planet; the outer, Jovian planets (Jupiter, Saturn, Uranus, Neptune). Jupiter and Saturn have an elemental composition similar to the Sun's, predominantly hydrogen and helium. Uranus and Neptune, in contrast, consist predominantly of ice.
protoplanetary disk
a rotating circumstellar disk of dense gas surrounding a young newly formed star. It is thought that planets are eventually formed from the gas and dust within this formation.
planetesimals
small planetary objects that form through the action of gravity during the birth of a solar system.
protoplanets
regions of condensed matter that serve as a starting point for the formation of a planet.
nebular theory
theory that the sun and the planets condensed out of a spinning cloud of gas and dust.
differentiation
by this process, protoplanets and large planetesimals developed internal layering early in their history; due to increasing heat from two sources: the transformation of kinetic energy into thermal energy during collisions, and the decay of radioactive elements.
meteorites
solid objects falling from space that land on a planet. Heavy bombardment in the early days of the solar system pulverized surfaces of the planets leaving huge craters and contributing to heating.
DEFORMATION
a process by which rocks change shape, tilt, or break in response to squeezing, stretching, or shearing. The process of forming a mountain not only uplifts the surface of the crust, but also causes rocks to undergo this process.
joints
geologic structures produced from deformation; cracks. Develop in response to tensional stress in brittle rock: a rock splits open because it has been pulled slightly apart. Some form when a rock cools and contracts, others when rock layers formerly at depth undergo a decrease in pressure as overlying rock erodes away, and thus change shape slightly.
faults
geologic structures produced from deformation; fractures along which one body of rock slides past another. A pulse of rapid deformation causes these to form.
folds
geologic structures produced from deformation; the curving of rock layers, bends or wrinkles. Slow deformation yields these. May be defined by curving dikes, sills, or veins.
foliation
geologic structures produced from deformation; layering resulting from the alignment of mineral grains or the development of compositional bands.
mountain belts
Mountains do not occur in isolation, but rather as a part of linear ranges variously called _____, orogenic belts, or orogens. These develop because of subduction at convergent plate boundaries, rifting, continental collisions, and locally, because of motion on transform faults.
orogeny
From the Greek word oros, meaning mountain, and genesis, meaning formation. It's a mountain-building event with a limited lifetime. The process begins, lasts for tens of millions of years, and then ceases. After this process ceases, erosion may eventually bevel the land surface almost back to sea level, sometimes in a little as 50 million years.
undeformed
an outcrop at which the beds have the same orientation that they had when first deposited. It contains no geologic structures other than a few joints.
characteristics of deformation
When beds no longer have the same shape and position that they had when first formed, and the shape and orientation of grains has changed. Deformation includes one or more of the following: a change in location (translation), a change in orientation (rotation), or a change in shape (distortion),
strain
the irreversible change in shape that deformation causes. There are different variations: if a layer of rock becomes longer, it has undergone 'stretching'. If the layer of rock becomes shorter, it has undergone 'shortening', and if a change in shape involves the movement of one part of a rock body past another so that the angles between features in the rock change, the result is 'shear strain'.
brittle deformation
type of deformation; a material breaks into two or more pieces, like a plate shattering on the floor. JOINTS and FAULTS are these types of structures. During this process, many chemical bonds within the rock break at once so that rocks can no longer hold together.
ductile deformation
type of deformation; a material changes shape without breaking, like a ball of dough squeezed beneath a book. FOLDS and FOLIATIONS are these types of structures. During this process, some chemical bonds do break but new ones quickly form, so that rocks do not separate into pieces as they change shape.
temperature
behavior of rock dependence; warm rocks tend to deform ductilely, whereas cold rocks tend to deform brittlely. Like a candle, rocks will become malleable when subjected to heat.
pressure
behavior of rock dependence; under great pressures deep in the Earth, rock behaves more ductilely than it does under low pressures near the surface. Pressure effectively prevents rock from separating into fragments.
deformation rate
behavior of rock dependence; a sudden change in shape causes brittle deformation, whereas a slow change in shape causes ductile deformation. For example, if you hit a marble bench with a hammer, it shatters, but if you leave it alone for a century, it gradually sags without breaking.
composition
behavior of rock dependence; some rock types are softer than others; for example, halite (rock salt) can deform ductilely under conditions in which granite behaves brittlely.
the brittle-ductile transition
considering that pressure and temperature both increase with depth in the Earth, geologists finds that in typical continental crust, rocks behave brittlely above about 10-15 km, whereas they behave ductilely below. Earthquakes in continental crust happen only above this depth because these earthquakes involve brittle breaking.
stress
Geologists use this word instead of force when talking about the cause of deformation. Defined as: the action on a plane as the force applied per unit area of the plane. Written as an equation this becomes: _____ = force/area. During mountain building, the force of one plate interacting with another is distributed across the area of contact between the two plates, so the deformation resulting at any specific location actually depends on the ____ developed at that location, not on the total force involved in the plate interaction.
compression
type of stress; develops when a rock is squeezed. Occurs during growth of a collisional mountain range, convergent plate boundaries.
tension
type of stress; occurs when a rock is pulled apart. Occurs during growth of a continental rift, divergent plate boundaries.
shear stress
type of stress; develops when one side of a rock body moves sideways past the other side. Occurs at faults, transform plate boundaries.
pressure
type of stress; refers to the special stress condition in which the same push acts on all sides of an object. A diver feels this when submerged.
systematic joints
category of joint; long planar cracks that occur fairly regularly through a rock body.
non systematic joints
category of joint; short cracks that occur in a range of orientations and are randomly spaced.
veins
if groundwater seeps through joints for a long period of time, minerals such as quartz or calcite can precipitate out of the groundwater and fill the joint. Such mineral-filled joints are called ____ and look like white stripes cutting across a body of rock.
hanging-wall block
in the case of nonvertical faults (those that slope at an angle), this is the rock above the fault plane.
footwall block
in the case of nonvertical faults (those that slope at an angle), this is the rock below the fault plane.
dip-slip faults
type of fault; sliding occurs up or down the slope of the fault (therefore, up or down the dip). Types of these faults include: normal faults and thrust/reverse faults.
strike-slip faults
type of fault; one block slides past another (therefore, parallel to the strike line). Form along transform fault boundaries.
oblique-slip faults
type of fault; sliding occurs diagonally on the fault plane.
thrust/reverse faults
type of dip-slip fault; the hanging-wall block moves up the slope of the fault. Thrust faults differ from reverse only in terms of the fault-plane's slope: thrust have a slope of <35 degrees, whereas reverse faults have a slope of >35 degrees. Accommodate shortening of the crust with strong compressional forces.
Normal faults
type of dip-slip fault; the hanging-wall block moves down the slope of the fault relative to the footwall block. Accommodate lengthening, or extension, of the crust.
displacement
to recognize a fault, there are generally offset distinctive beds, in such cases, the fault is the plane on which offset occurs. Geologists refer to this offset as the ____ on the fault. In some cases, faults juxtapose two different rock units so the fault is the surface of contact between the two units.
fault scarp
displacement on a dip-slip or oblique-slip fault makes a small step on the ground surface; and because faults tend to break up rock, the fault may be preferentially eroded. If this happens, the fault trace (the line of intersection between the fault and the ground surface) will be marked by a linear valley.
shear zones
the shear on some faults takes place under ductile conditions at depth in the crust. Where this happens, rock does not break up into breccia or gouge along the fault zone, but rather shears ductilely to form a band of fine-grained foliated rock called mylonite. The fine grain size of mylonite results not from brittle fracturing during shear, but rather from a type of metamorphic recrystallization that subdivides large grains into small ones. These ductile moving faults are called ____.
detachment fault
numerous related faults are often found in groups called fault systems. Individual faults in a system may merge at depth with a nearly horizontal _____.
the nature of fault systems
the faulting in a thrust-fault system shortens the crust; slip makes slices of the crust overlap like shingles. Faulting in normal-fault systems, on the other hand, stretches the crust. In such systems, elongate basins separate high blocks of rock. Individual basins may be bounded on each side by a normal fault dipping toward the basin. Typically, normal faults become shallower with depth and merge with a detachment fault.
graben
a fault-bounded basin. The central block formed from a normal fault, these produce an elongated valley bounded by uplifted structures called horsts.
horst
the high block between two grabens.
hinge
component of folds; refers to the portion of the fold where curvature is the greatest.
limbs
component of folds; the sides of the fold that show less curvature.
axial plane
component of folds; an imaginary surface that encompasses the hinges of successive layers.
anticline
type of fold; a fold that has an archlike shape in which the limbs dip away from the hinge, involves sedimentary layers in the center and progressively younger layers away from the center; the stripes are symmetrically positioned around the hinge.
syncline
type of fold; a fold with a trough-like shape in which the limbs dip down toward the hinge. Involves sedimentary layers, the youngest layers crop out in the center and the oldest at the margins.
monocline
type of fold; a fold that has the shape of a carpet draped over a stairstep.
open and tight folds
aspects of a fold; if the angle between the limbs is large, then the fold is an open fold, but if the angle between the limbs is small, then the fold is a tight fold.
nonplunging and plunging folds
aspects of a fold; if the hinge is horizontal, the fold is called a nonplunging fold, but if the hinge is tilted, the fold is called a plunging fold. Layers in a plunging fold have a U-shape on the ground surface.
dome
a fold in the shape of an overturned bowl. The oldest layer occurs in the center.
basin
a fold shaped like a right-side up bowl. The youngest layer occurs in the center.
forming folds
folds develop in two principal ways. During formation of flexural folds, a stack of layers bends, and slip occurs between the layers. And flow folds form when the rock overall is so soft that it behaves like weak plastic; these folds develop simply because different parts of the rock body move at different rates.
tectonic foliation
the layering created by the alignment of deformed and/or reoriented grains. Overall, deformation can produce inequant grains and can cause them to align parallel with one another, thereby generating metamorphic foliation in the rock.
igneous activity during orogeny
in mountain belts formed along convergent plate boundaries, magma forms as a consequence of subduction. In rifts, stretching and thinning of lithosphere causes decompression melting of the underlying mantle. And during continental collision, melting may take place where deep portions of the crust undergo heating.
sedimentation during orogeny
weathering and erosion in mountain belts generate vast quantities of sediment. This sediment tumbles down slopes and gets carried away by glaciers or streams that transport it to low areas where it accumulates in large fans or deltas. The weight of collisional mountain belts pushes down the surface of the lithosphere, thereby producing a deep sedimentary basin at the border of the range.
metamorphism during orogeny
contact metamorphic aureoles form adjacent to igneous intrusions in orogens. Regional metamorphism occurs during compression during mountain building produces faults on which one part of the crust thrusts over another. Rock of the footwall can end up at great depth and thus can be subjected to high temperature and pressure. Because deformation accompanies this process, the resulting metamorphic rocks contain tectonic foliation.
uplift
the process by which the surface of the Earth moves vertically from a lower to a higher elevation. Mountain building produces substantial ___ of the Earth's surface.
crustal root
a mountain range with a low-density _____ has less mass overall than a mountain range underlain by dense mantle, and so it exerts less pull on a plumb bob. These are important because without their buoyancy, mountain ranges would not be so high.
isostasy
the condition that exists when the buoyancy force pushing lithosphere up equals the gravitational force pulling lithosphere down. In most places, isostatic equilibrium exists at the surface of the crust, so that the surface elevation of the crust reflects the level at which the lithosphere naturally floats.
isostatic compensation
if a geologic event happens that changes the density or thickness of the lithosphere, then the surface of the crust slowly rises or falls to reestablish isostatic equilibrium. For example, when glaciers grow during ice ages, their weight depresses the surface of the crust, and when they melt away after ice ages, the surface of the crust rises. Also the process of mountain uplift is commonly a manifestation of this process.
cuesta
In some cases, the geometry of geologic structures affects the shape of mountains. Mountain ridges formed by tilted layers of rock typically have an asymmetric shape, with a steep face on one side (where a cliff cuts across a layer) and a gentle slope on the other side (parallel to the layering, where the top layer becomes the surface of the hill); asymmetric.
hogback
In some cases, the geometry of geologic structures affects the shape of mountains. If beds dip steeply, they form this narrow, more symmetrical ridge.
limitations of uplift
mountains much higher than Mt. Everest cannot exist on the Earth for two reasons. Erosion attacks mountains as soon as they rise, and in some cases it can tear mountains down as fast as uplift occurs. Also, rock does not infinite strength; as mountains rise, the weight of the overlying rock presses down on the rock that is now deeply buried at depth in the crust. The rock buried at depth is gradually growing warmer and softer because of heat rising from the Earth's interior, activating a process called orogenic collapse.
exotic terranes
the compression created by a convergent boundary causes a mountain range to rise. During this time, offshore island volcanic arcs, oceanic plateaus, and small fragments of continental crust may drift into the convergent margin. These blocks are too buoyant to subduct, so they collide with the convergent margin and accrete, or attach, to the continent.Geologists refer to such blocks before they attach as ____ and after they have attached as accreted terranes.
accretionary orogens
orogens that grow laterally by the attachment of exotic terranes; Once an exotic terrane accrete to a continent, a new subduction zone typically forms on the ocean side of the terrane, and a new volcanic arc develops on top of the terrane.
fold-thrust belt
when plate movements push the contingent tightly against the subduction zone, compression on the continent side of the volcanic arc generates a ____. In such belts, a thrust-fault system has developed above a nearly horizontal detachment fault, and folds form as strata are pushed up from the fault.
craton
consists of crust that has not been affected by orogeny for at least 1 billion years. Because of this, their crust has become quite cool, and therefore relatively strong and stable. Variations in the dip and thickness of these strata define regional basins, arches, and domes. Divided into two provinces: shields and the cratonic platform.
shield areas
a province of a craton; in these areas, we find intensively deformed metamorphic rocks - abundant examples of shear zones, flow folds, and tectonic foliation. These orogens are so old that erosion has worn away the original topography, in the process exposing deep crustal rocks at the Earth's surface.
the cratonic platform
a province of a craton; in this area, we can't see the Precambrian rocks and structures, except where they are exposed by deep erosion. Younger strata display less intense deformation. Includes two classes of structures: regional basins and domes, and local zones of folds and faults.
epeirogeny
geologists refer to the broad vertical movements that generate huge, but gentle, mid-continent domes and basins as ____.
THE EARTHQUAKE HYPOCENTER
a sudden rupture of intact rock or the frictional slip of rock on a fault produces seismic waves. These waves move outward from the point of rupture in all directions at once.
surface waves
waves traveling along the surface of earth; a single earthquake produces many kinds of waves, distinguished from each other by where and how they move; (R-waves and L-waves) waves that propagate along the planet's surface.
body waves
waves passing through the interior (body) of earth; a single earthquake produces many kinds of waves, distinguished from each other by where and how they move; (P-waves and S-waves) waves that pass through the interior of the planet. P-waves are compressional, similar to a spring, whereas S-waves are shear, resembling a moving rope.
wave front
the boundary between the rock through which a wave has passed and the rock through which it has not yet passed. Expands outward from the earthquake focus like a growing bubble.
seismic ray
the changing position of an imaginary point on a wave front as the front moves through rock. Perpendicular to wave fronts, so that each point on the wave front allows a slightly different ray.
travel time
the time it takes for a wave to travel from the focus to a seismograph station along a given ray is the ___ along that ray.
factors influencing seismic travel
the ability of a seismic wave to travel through a certain material and the velocity at which travels depend on the character of the material. Density (mass per unit volume), rigidity (how stiff or resistant to twisting a material is), and compressionability (how much a material's volume changes in response to squashing).
seismic travel velocity
P-waves travel at 8 km per second in peridotite (ultramafic rock), but only 3.5 km per second in sandstone. Waves accelerate or slow down if they pass from one rock to another. P-waves in rock travel about 10 to 25 times faster than sound waves in air. Additionally, seismic waves travel faster in a solid than in a liquid. Only P-waves can travel through a liquid and are faster than S-waves in all materials.
reflection
the phenomenon of light bouncing off a surface. Since seismic energy travels in the form of waves, seismic waves reflect or refract when reaching the interface between two rock layers if the waves travel at different velocities in the two layers.
refraction
the phenomenon of light bending when passing through a surface. As a rule, if waves enter a material through which they will travel more slowly, the rays representing the waves bend away from the interface. If the waves enter a material through which they will travel faster, the rays bend toward the interface.
low-velocity zone
between about 100 and 200 km deep in the mantle beneath oceanic lithosphere, seismic velocities are slower than in the overlying lithospheric mantle. Within this zone, the prevailing temperature and pressure conditions cause peridotite to melt partially, by up to 2%, the melt coats solid grains and fills voids between grains.
seismic-velocity discontinuities
occur at depths where pressure causes atoms in minerals to rearrange and pack together more tightly, thereby changing the rock's physical character. Corresponds to a phase change.
P-wave shadow zone
the zone 103° - 142° from the epicenter of an earthquake; explained by refraction of P-waves encountering the core-mantle boundary.
core-mantle boundary
the presence of a shadow zone means that deep in the Earth a major interface exists where seismic waves abruptly refract down (implying that the velocity of seismic waves suddenly decreases). This interface lies at a depth of about 2900 km. The density contrast across this boundary is greater than the density contrast between the crust and water.
S-wave shadow zone
the zone ≥103° from the epicenter of an earthquake; suggests the outer core is a liquid, careful observations of P-wave refraction patterns indicate inner core is a solid. This means that S-waves cannot pass through the core at all.
velocity-versus-depth curve
S-waves: occur in the crust, mantle, and inner core, 7 or less km per second. P-waves: occur in the crust, mantle and core, 6-14 km per second.
seismic tomography
A method that uses the seismic waves from earthquakes recorded on thousands of seismographs all over the world to sweep Earth's interior in many different directions and construct a three-dimensional image of what's inside.
seismic-reflection profile
To view rock structure beneath sea floor, strong low-frequency sounds are produced by explosions (depth charges) or air guns. These sound waves penetrate beneath the seafloor and reflect off the contacts between rock layers and fault zones just like sonar reflects off the bottom of the sea.
EARTHQUAKE
episode of ground shaking. Most are a consequence of lithosphere plate movement; they punctuate each step in the growth of mountains, the drift of continents, and the opening and closing of ocean basins.
seismicity
earthquake activity, occurs for several reasons: formation of a new fault, slip on existing fault, sudden change in the arrangement of atoms in the minerals comprising rock, movement of magma in a volcano, explosion of volcano, giant landslide, meteorite impact, or underground nuclear-bomb tests.
hypocenter (focus)
place in the earth where rock ruptures and slips, or the place where an explosion occurs
epicenter
point on the surface of the earth that lies directly above the hypocenter
displacement
amount of slip on the fault, by measuring the distance between two ends of a marker, such as distinctive sedimentary bed or igneous dike that's been offset by a fault, geologists can define this.
fault trace (or fault line)
the intersection between a fault and the ground surface.
fault scarp
in places where an active normal or reverse fault intersects the ground, one side of the fault moves vertically with respect to the other side, creating a small step called a______.
elastic-rebound theory
overall image of how earthquakes occur; After either faulting event, stress drops and the elastic strain stored in rock decreases - the rock rebounds so layers near the fault are no longer bent. Friction stops the movement and the fault locks, until stress builds up enough again to cause slip. (first explained by HF Reid)
stick-slip behavior
start and stop movement on a fault; between faulting events, stress builds up and in some cases the stress causes intact rocks to rupture and a new fault to form. Or in other cases, stress overcomes friction on an existing fault and the fault slips again.
fault creep
in some cases, movement on faults in the upper 15-20 km of the continental crust takes place slowly and steadily, without generating earthquakes. Seismologists speculate that this occurs in particularly weak rock, which can change shape without breaking or can slip smoothly without creating shock waves.
seismic waves
earthquake energy traveling in the form of waves
compressional waves
waves in which particles of material move back and forth parallel to the direction in which the wave itself moves
shear waves
waves in which particles of material move back and forth perpendicular to the direction in which the wave itself moves
P-waves
compressional body waves - push/pull waves; 1st, fastest, & go through solids & liquids
S-waves
shear body waves - side-to-side waves; 2nd, slower, & go though solids;
R-waves
surface waves that cause the ground to ripple up and down
L-waves
surface waves that cause the ground to ripple back and forth in a snake-like movement. Cause the rolling motion of the ground; have the largest amplitude and arrive over a long period of time.
seismograph
machine that can systematically record the ground motion from an earthquake happening anywhere on earth; , a measuring instrument for detecting and measuring the intensity and direction and duration of movements of the ground (as an earthquake)
seismogram
waves traced by the pen on a seismograph provide a record of the earthquake
arrival time
instant at which an earthquake wave appears at the seismograph station
travel time curve
plots the time since the earthquake began on the vertical axis and the distance to the epicenter on the horizontal axis. Used to determine the distance of an epicenter, start by measuring the time difference between P- and S-waves on the seismograph.
triangulation
to determine the map position of the epicenter, we use this method, by plotting the distance between the epicenter and three stations across the globe. The epicenter lies at the intersection of the three circles, for this is the only point at which the epicenter has the appropriate measured distance from all three stations.
Mercalli intensity scale
defines the intensity of an earthquake by the amount of damage it causes; developed in 1902 by Italian scientist Giuseppe Mercalli. Denoted the measure of intensity with M followed by a Roman numeral - such MVII or MXI
earthquake magnitude scales
number that indicates its relative size, as determined by measuring the maximum amplitude of ground motion recorded by a seismograph at a given distance from the epicenter.
Richter scale
number used to compare against magnitude scale by measuring the amplitude of the largest deflection generated in response to seismic waves that have a period of one second; developed by Charles Richter 1935. The levels are logarithmic, thus a magnitude 8 is 10x greater than a magnitude 7, and 1000x greater than magnitude 5 earthquake.
oceanic crust characteristics
specific gravity of 3.0, depth of 5-7 km
continental crust characteristics
specific gravity of 2.7, depth of 20-70 km
upper mantle characteristics
specific gravity of 3.3, depth of 100-200 km, composed entirely of peridotite
low-velocity zone (within the mantle) characteristics
specific gravity of 3.5, depth of 410 km, partial melting occurs here.
transition zone (within the mantle) characteristics
specific gravity of 3.7, depth of 410-660 km, area of mineral phase change
lower mantle characteristics
specific gravity 3.8 to 5.5, depth of 660-2900 km
outer core characteristics
specific gravity of 5-9, depth of 3000-5000 km, consists of liquid iron alloy
inner core characteristics
specific gravity of 11-14, depth of 5000-6000 km, consists of solid iron alloy
local magnitude
because of the Richter's scales limitations on distance, a number on the original Richter's scale is now called this, (ML)
surface-wave magnitude
to apply Richter's concept to the description of distant earthquakes, seismologists developed a new scale based on measuring the amplitudes of certain R-waves, (Ms).
body-wave magnitude
to describe the size of deeper earthquakes, seismologists determined this type of measure, (mb), which is based on measurement of P-waves.
Moment magnitude
(Mw), because the other measures of magnitude could not accurately define the sizes of very large earthquakes, seismologists developed this scale. To calculate, it is necessary to measure the amplitude of a number of different seismic waves, determine the area of the slipped portion of the fault that moved, determine how much slip occurred, and define physical characteristics of the rock that broke during faulting. Typically, the larger the area that slipped and amount of displacement, the greater the earthquake
seismic belts (or seismic zones)
earthquakes do not take place everywhere on the globe, by plotting the distribution of earthquake epicenters on a map, seismologists find that most, but not all, earthquakes occur in these narrow areas, most following plate boundaries.
shallow-focus earthquake
classification of an earthquake based on the hypocenter depth; occur in the top 20 km of the earth. Cause the most damage, because the earthquake waves they produce do not lost much energy before vibrating the Earth's surface.
intermediate-focus earthquake
classification of an earthquake based on the hypocenter depth; take place between 20-300 km. Only in subducting oceanic plates.
deep-focus earthquake
classification of an earthquake based on the hypocenter depth; occur down to a depth of about 670 km. Only in subducting oceanic plates.
divergent plate-boundary seismicity
two kinds of faults develop in these regions: along spreading segments, newly formed crust at or near the mid-ocean ridge stretches and ruptures, generating normal faults, whereas along the transform faults that link spreading segments, strike-slip faulting occurs. Seismicity along mid-ocean ridges takes place at shallow depths (less than 10 km).
convergent plate-boundary seismicity
shallow-focus earthquakes occur in both the subducting plate and the overriding plate. The bending that occurs during subduction stretches the downgoing plate and generates small normal faults in the plate. Large thrust faults develop along the contact between the downgoing and overriding plates. Most of the Earth's seismic energy is released at these plate boundaries.
Wadati-Benioff zone
A sloping band of seismicity defined by intermediate and deep focus earthquakes that occur in the downgoing slab of a convergent plate boundary.
transform plate-boundary seismicity
at this type of plate boundary, most faulting results in strike-slip motion. The majority of these faults in the world link segments of oceanic ridges, but a few, such as the Sand Andreas Fault and the Alpine Fault of New Zealand cut across continental lithosphere, these large ones on land can cause great disaster.
earthquakes at continental rifts
the stretching of continental crust at these rifts generates normal faults. Active rifts today include the East African Rift, the Basin and Range Province and the Rio Grande Rift. In all these places, shallow-focus earthquakes occur, similar in nature to the earthquakes at mid-ocean ridges.
earthquakes at collision zones
zones where two continents collide after the oceanic lithosphere that once separated them has been completely subducted yield great mountain ranges such as the Alpine-Himalayan chain. The most common movements in these zones is on thrust faults, which formed when the crust was compressed, or squeezed.
intraplate earthquakes
some earthquakes occur in the interiors of plates and are not associated with plate boundaries, active rifts, or collision zones. These type of earthquakes account for only about 5% of the earthquake energy released in a year, all of them have a shallow hypocenter. Thought to be caused by force being applied to the boundary of a plate causing the interior of the plate to break at weak, preexisting fault zones, some of which date back to the Precambrian. Alternatively, the activity may be due to forces resulting from shear between the lithosphere and asthenosphere.
induced seismicity
most earthquakes happen independent of human activity, but the timing of some earthquakes relative to human-caused events suggest that, in certain cases, people can influence seismicity. These are seismic events caused by actions of people, generally occurs in response to changes in groundwater pressure.
the magnitude of the earthquake
factor in the nature and severity of earthquake shaking; larger-magnitude events release more energy.
the distance from the hypocenter
factor in the nature and severity of earthquake shaking; earthquake energy decreases as waves pass through the Earth
the nature of the substrate at the location
factor in the nature and severity of earthquake shaking; the character and thickness of different materials beneath the ground surface. In places underlain by unconsolidated sediment or landfill, earthquake waves tend to be amplified and thus cause more ground motion
the frequency of earthquake waves
factor in the nature and severity of earthquake shaking; where frequency equals the number of oscillations that pass a point in a specified interval of time.
sieche
ground motion from earthquakes can cause water in lakes, bays, reservoirs, and pools to slosh back and forth, in some cases thousands of kilometers from the epicenter. The water's rhythmic movement can build up waves almost 10 m high and can last for hours.
liquefaction
the abrupt loss of strength of a wet sediment (either sand or clay) in response to ground shaking. Can cause major damage during an earthquake, buildings whose foundations lie in liquified material may sink or even tip over.
tsunamis
A giant wave caused by an earthquake on the ocean floor; water from the upthrust sea floor began moving outward from above the fault zone, a process that generates a series of giant waves traveling at speeds of about 800 km/hour (500mph).
seismic-risk (or seismic hazard assessment)
The earthquake damage that can be expected over the long term for a specified region, such as a county or state, usually measured in terms of average dollar loss per year.
recurrence interval
seismologists base long-term earthquake predictions on two pieces of information: the identification of seismic zones and the ____ (the average time between successive events).
annual probability
this probability is the 1/earthquake recurrence interval
seismic gaps
seismologists mark these zones where a known active fault has not slipped for a long time as particularly dangerous.
Alpha emission
type of radioactive decay; emission of 2 protons and 2 neutrons (an alpha particle). The mass number of the element is reduced by 4 and the atomic number is lowered by 2.
Beta emission
type of radioactive decay; an electron (beta particle) is given off from the nucleus. Mass number remains unchanged and the atomic number increases by 1.
Electron capture
type of radioactive decay; an electron is captured by the nucleus, the electron combines with a proton to form a neutron. Mass number remains unchanged and the atomic number decreases by 1.
Rocks
aggregates of mineral crystals or grains, and masses of natural glass; a coherent, naturally occurring solid, consisting of an aggregate of minerals or a mass of glass.
Dipole
the nature of Earth's magnetic field, like the familiar magnetic field around a bar magnet, has a North and South pole. The magnetic field is drawn with field lines, the paths along which magnets would align, or charged particles would flow, if placed in the field.
Earth's atmosphere
an envelope of gas surrounding Earth consisting of 78% nitrogen (N2) and 28% oxygen (O2), with minor amounts 1% of argon, carbon dioxide, methane, etc. And 99% of the gas in the atmosphere lies below 50km.
atmospheres (atm)
Measure of pressure or push in units of force, per unit area. 1 atm = 1.04 kilograms per square centimeter.
Hydrosphere
sphere; Surface water along with groundwater, Earth consists of 70% surface water (oceans, lakes, and streams).
Topography
physical features of the land surface represented by changes in elevation.
Elemental composition of Earth
iron (35%), oxygen (30%), silicon (15%), and magnesium (10%), and the remaining 10% consists of 88 naturally occurring elements.
Organic chemicals
carbon-containing compounds that either occur in living organisms, or have characteristics that resemble the molecules within living organisms. Examples - oil, protein, plastic, fat, and rubber.
Mineral
a naturally occurring solid, formed by geologic processes, has a crystalline structure and a definable chemical composition, and is generally inorganic.
Glass
a solid in which atoms are not arranged in an orderly pattern. Forms when a liquid freezes so fast that atoms do not have time to organize into an orderly pattern.
Igneous rocks
rocks which develop when hot molten rock cools and freezes solid.
Sedimentary rocks
form from grains that break off preexisting rock and become cemented together, or from minerals that precipitate out of a water solution.
Metamorphic rocks
created from preexisting rocks which undergo changes, such as the growth of new minerals in response to pressure and heat, and/or as a result of squashing, stretching, or shear.
Metals
solids composed of metal atoms (such as iron, aluminum, copper, and tin). Within this type of solid, outer electrons are able to flow freely.
Alloy
a mixture containing more than one type of metal atom. Example - bronze is a mixture of copper and tin.
Melts
form when solid materials become hot and transform into liquid, example - molten rock.
Magma
molten rock beneath Earth's surface.
Lava
molten rock that has flowed out onto Earth's surface.
Volatiles
materials that easily transform into gas at the relatively low temperatures found at the Earth's surface.
Silicate minerals
the most common minerals in the Earth. Contain silica (SiO2) mixed in varying proportions with other elements (typically iron, magnesium, aluminum, calcium, potassium, and sodium).
Felsic, intermediate, mafic, ultramafic
The four classes of igneous silicate rocks based on the proportion of silicon to iron and magnesium. As the proportion of silicon in a rock increases, the density decreases, thus felsic rocks are less dense than mafic. In order, from greatest to least proportion of silicon to Fe/Mg are:
Granite
a felsic rock with large grains. Intrusive, phaneritic igneous rock.
Basalt
a mafic rock with small grains. Extrusive, aphanitic igneous rock.
Gabbro
a mafic rock with large grains. Intrusive, phaneritic igneous rock.
Peridotite
an ultramafic rock with large grains. intrusive, phaneritic igneous rock.
3.5km (2 miles)
the distance that the world's deepest mine-shaft penetrates into the Earth beneath South Africa.
12km
the distance of the deepest well ever drilled, hole in northern Russia. Penetrates only about 0.03% of the Earth.
Crust
outer surface level of Earth; composed of granite, basalt, and gabbro. Continental: mostly about 35-40km thick . Oceanic: about 7-10km thick. Oxygen, by far the most abundant element.
Mantle
forms a 2885-km-thick layer surrounding the core. In terms of volume, it is the largest part of the Earth. It consists entirely of ultramafic rock, peridotite.
Upper mantle
sublayer of the mantle, depth of 660km.
Lower mantle
deeper sublayer of the mantle, depth of 660km to 2900km.
Transition zone
the bottom portion of the upper mantle, the interval lying between 400km and 660km deep. Here within the Earth, the character of the mantle undergoes a series of abrupt changes.
The core
center of the Earth, consists mainly of iron alloy.
Outer core
core division; between 2900 and 5155km deep. Liquid iron alloy, it exists as a liquid because the temperature here is so high that even the great pressures squeezing the region cannot lock atoms into a solid framework. This liquid iron alloy is able to flow; this flow generates Earth's magnetic field.
Inner core
core division; from a depth of 5155km down to Earth's center at 6371km. A radius of about 1220km, is solid iron-nickel alloy, can reach temperature of 4700 degrees C. Solid in nature because of subjection to greater pressure, keeps atoms from wandering. Rotates faster than the rest of Earth because of the force applied to it by the Earth's magnetic field.
Lithosphere
rigid outer layer of Earth, 100-150km thick. Consists of the crust plus the uppermost part of the mantle.
Asthenosphere
layer that lies below the lithosphere, and is the portion of the mantle in which rock can flow (slowly; 10-15cm per year) despite still being solid. Entirely within the mantle and lies below a depth of 100-150km.
Pangaea
the supercontinent; existence proposed by Wegener, suggested that the supercontinent later fragmented into separate continents that then drifted apart, moving slowly to their present positions.
Plate tectonics
theory confirmed by 1968, geologists had developed the complete model of continental drift, sea-floor spreading, and subduction. Within this model, Earth's lithosphere consists of about 20 distinct pieces, or plates, that move relative to each other.
Continental drift hypothesis
Alfred Wegener's suggestion that the positions of the continents change through time as they drift away from each other. The flaw was that he lacked a plausible moving mechanism.
Continental drift evidence
the fit of the continents, locations of past glaciations, the distribution of equatorial climatic belts, the distribution of fossils, and matching geologic units.
Paleomagnetism
some rocks develop their magnetization, their ability to produce a magnetic field, at the time that the rocks themselves formed. Such rocks, preserve a record of the Earth's magnetic field at known times in the past.
Apparent polar-wander path
the record of paleomagnetism revealed that the location of Earth's magnetic poles had been changing through geologic time. This 'wandering' meant that Earth's magnetic poles do not move with respect to fixed continents. Rather, continents move relative to each other while the Earth's magnetic poles stay roughly fixed.
Bathymetry
the shape of the sea floor surface. Investigation of the sea-floor revealed the presence of several important features: mid-ocean ridges, deep-ocean trenches, seamount chains, and fracture zones.
Mid-ocean ridges
elongate submarine mountain ranges whose peaks lie only about 2-2.5km below sea level. Consist of a ridge axis, are roughly symmetrical, and can include escarpments, axial troughs, and valleys. Examples - Mid-Atlantic Ridge, East Pacific Rise, Southeast Indian Ocean Ridge.
Abyssal plains
the broad, relatively flat regions of the ocean that lie at a depth of about 4-5km below sea level.
Deep-ocean trenches
along much of the perimeter of the Pacific Ocean, the ocean floor reaches astounding depths of 8-12km. These areas define elongate troughs, and they border volcanic arcs, the curving chains of active volcanoes.
Seamount chains
in addition to islands that rise above sea level, seamounts have been detected (isolated submarine mountains), once volcanoes but no longer erupt.
Fracture zones
the ocean floor is diced up by narrow bands of vertical fractures. Lie roughly at right angles to mid-ocean ridges, effectively segmenting the ridges into small pieces.
Magnetic anomaly
the difference between the expected strength of the Earth's main field at a certain location and the actual measure strength of the magnetic field at that location. Places where the field strength is stronger that expected are positive anomalies, and weaker are negative anomalies.
Marine magnetic anomaly
the compiled data from many marine cruises which defined a distinctive, striped and alternating bands of paleomagnetism.
Magnetic reversals
times when the Earth's magnetic field flips from normal to reversed polarity, or vice versa. When the Earth has reversed polarity, the south magnetic pole lies near the north geographic pole, and the north magnetic pole lies near the south geographic pole. Process is a reflection of the changes in the configuration of flow in the outer core.
Spreading rate
the crust moves away from the Mid-Atlantic Ridge axis at a rate of 1cm per year. This velocity of sea-floor spreading is determined by the relationship between the paleomagnetic anomaly-stripe's width and the reverse polarity duration, the data reveals that the rate of spreading has been fairly constant.
Sea-floor spreading
A proposition in 1960, by Princeton University professor Harry Hess, that continents drift apart because new ocean floor forms between them by this process.
Subduction
Sea-floor spreading proponents, Hess and others realized that in order for the circumference of the Earth to remain constant through time, ocean floor must eventually sink back into the mantle. This sinking process consumes the ocean floor between two continents, and the continents move toward one another.
Magnetic declination
the angle between the direction that a compass needle points at a given location and the direction of the "true" (geographic) north. Through this process, the magnetic poles never stray more than 15 degrees of latitude from the geographic pole.
Magnetic inclination
the freely pivoting up and down compass needle's angle of tilt relative to the location upon the Earth's surface. At the equator, the specialized magnetic needle would position horizontally and at a magnetic pole it would point straight down.
Paleopole
a reference to the supposed position of the Earth's magnetic pole at a time in the past.
Plates
the separated lithosphere into distinct pieces. Twelve major 'pieces' and several minor. Consist of active margins and passive margins between them.
Continental shelf
a thick accumulation of sediment (10-15km), the surface of this sediment layer is this broad, shallow region.
Divergent plate boundary
a plate boundary at which two plates move apart from one another by process of sea-floor spreading. Mid-ocean ridges or simply a ridge. New crust is formed at ridges through the buoyant rising of magma from beneath the surface and solidifies to create new crust at the ridge axis.
Convergent plate boundary
a plate boundary at which two plates move toward one another so that one plate sinks beneath the other. Subduction zones; Engage the sinking process known as subduction, between plates, consuming old oceanic lithosphere due to high density. Can simply be called trenches.
Transform plate boundary
a plate boundary at which one plate slips along the side of another plate. No new plate is formed and no old plate is consumed. But the grinding between the plates generates frequent and destructive earthquakes.
Transform fault
actively slipping segment of a fracture zone between two ocean ridge segments, these faults make a third type of plate boundary, transforms.
triple junction
a place where three plate boundaries intersect at a point.
Hot spots
volcanoes that exist as isolated points and appear to be independent of movement at a plate boundary, hot-spot volcanoes. Mostly are located on the interior of plates, away from boundaries.
Mantle plume
a column of very hot rock that flows upward until it reaches the base of the lithosphere. In this model, such deep-mantle plumes form because heat rising from the Earth's core is warming rock at the base of the mantle. A possible explanation to the formation of hot spots.
rifting
process where new divergent boundaries form when a continent splits and separates into two continents.
collision
process where a convergent boundary ceases to exist when a piece of buoyant lithosphere, such as a continent or island arc, moves into the subduction zone. Yield some of the most spectacular mountains/mountain ranges on the planet including the Himalayas and Alps.
Continental rift
a linear belt in which continental lithosphere pulls apart, the lithosphere stretches horizontally.
Ridge-push force
develops because mid-ocean ridges lie at a higher elevation than the adjacent abyssal plains of the ocean. The surface of the sea floor overall slopes away from the ridge axis. Gravity causes the elevated lithosphere at the ridge axis to push on the lithosphere that lies farther from the axis, thus new hot asthenosphere material rises from the gap later itself becoming lithosphere.
Convective flow
occurs within the asthenosphere, actively drags plates along and attributes partially for the mechanism shifting the plates along the Earth's surface.
Slab-pull force
the force that subducting plates apply to oceanic lithosphere at a convergent boundary, arises simply because lithosphere formed 10 million years ago is denser than asthenosphere, so it can sink into the asthenosphere. Thus once an oceanic plate starts to sink down into the mantle, it gradually pulls the rest of the plate along behind it.
Relative plate velocity
the speed of the movements of the plates with respect to the speed of the other plates' movements. Absolute plate velocity is a measure of the movement of any plates relative to a fixed point in the mantle.
Crystal lattice
A reference to the pattern structure of a mineral. A material in which atoms are fixed in an orderly pattern, a crystalline solid.
Crystal
a single, continuous (uninterrupted) piece of a crystalline solid bounded by flat surfaces called crystal faces that grew naturally as the mineral formed. Come in a variety of shapes - cubes, trapezoids, pyramids, octahedrons, hexagonal columns, blades, needles, and obelisks.
Crystal structure
the way in which the atoms are packed together within a mineral by chemical bonds. Five difference types of bonding can occur - covalent, ionic, metallic, Van der Waal's, and hydrogen.
Polymorphs
two different minerals which have the same composition but have different crystal structures.
Symmetry
the display of the pattern of atoms or ions within a mineral. Meaning that the shape of one part of a mineral is a mirror image of the shape of another part.
Melting
Mineral crystal formation type; form from a solidification of a melt, meaning the freezing of a liquid.
Precipitation
Mineral crystal formation type; form from a solution, meaning that atoms, molecules, or ions dissolved in water bond together out of water.
Solid-state diffusion
Mineral crystal formation type; form by type of diffusion, the movement of atoms or ions through a solid to arrange into a new crystal structure; process takes place very slowly.
Biomineralization
Mineral crystal formation type; form at interfaces between the physical and biological components of the Earth system by this process.
Fumerolic mineralization
Mineral crystal formation type; from directly from a vapor, occurs around volcanic vents or around geysers. At such locations, volcanic gases or steam enter the atmosphere and cool, so certain elements cannot remain in gaseous form.
Mineral crystal destruction
by melting, dissolving, or other chemical reactions.
Euhedral crystal
a mineral's growth that is uninhibited, has well-formed crystal faces.
Color
physical property of a mineral; results from the way a mineral interacts with light. A mineral absorbs certain wavelengths, so the color seen represents the color wavelengths the mineral did not absorb.
Streak
physical property of a mineral; refers to the color of a powder produced by pulverizing the mineral. Provides a fairly reliable clue to the mineral's identity, since the color of the mineral powder tends to be less variable than the color of the whole crystal.
Luster
physical property of a mineral; refers to the way a mineral surface scatters light. Metallic versus non-metallic in nature.
Hardness
physical property of a mineral; a measure of a minerals relative ability to resist scratching, and therefore represents the resistance of bonds in the crystal structure being broken. The atoms or ions in crystals of a hard mineral are more strongly bonded than those in a soft mineral.
Specific gravity
physical property of a mineral; represents the density of a mineral, as specified by the ratio between the weight of a volume of the mineral and the weight of an equal volume of water a 4 degrees C.
Crystal habit
physical property of a mineral; refers to the shape (morphology) of a single crystal with well-formed crystal faces, or to the character of an aggregate of many well-formed crystals that grew together as a group. Depends on the internal arrangement of atoms in the crystal, for this controls the geometry of the crystal faces and the angular relationships among the faces.
Fracture and cleavage
physical property of a mineral; different minerals fracture in different ways, depending on the internal arrangement of atoms. If a mineral breaks to form distinct planar surfaces that have a specific orientation in relation to the crystal structure, then it's referred to as cleavage/cleavage planes. Forms in directions where the bonds holding the atoms together are the weakest.
Conchoidal fractures
fracture type; smoothly curving, clamshell-shaped surfaces; typically formed in quartz.
Special properties of minerals
some minerals have distinctive properties, such as calcite which reacts with dilute hydrochloric acid to produce carbon dioxide. Dolomite also reacts with acid, graphite can make clear markings, magnetite attracts a magnet, halite tastes salty, and plagioclase has striations on cleavage planes.
Silicates
mineral class; the fundamental component within these types of minerals in the Earth's crust is the silicon-oxygen tetrahedron anionic group, a silicon atom surrounded by four oxygen atoms that are arranged to define the corners of a tetrahedron, a pyramid-like shape with four triangular faces.
Oxides
mineral class; consist of metal cations bonded by oxygen anions. Examples - hematite and magnetite. Some contain a relatively high proportion of metal atoms, and thus are ore minerals.
Sulfides
mineral class; consist of a metal cation bonded to a sulfide anion. Examples - galena and pyrite. Many have a metallic luster. Can also be considered ores with high proportions of metal within the mineral.
Sulfates
mineral class; consist of a metal cation bonded to the anionic group. Many form by precipitation out of water at or near the Earth's surface. Example - gypsum.
Halides
mineral class; the anion within these types of minerals is a halogen ion (such as chlorine or fluorine).
Carbonates
mineral class; the molecule CO23 serves as the anionic group. Elements like calcium or magnesium bond to this group. Examples - calcite and dolomite.
Native metals
mineral class; consist of pure masses of a single metal, with metallic bonds. Copper and gold can appear in this way.
Silicate minerals
most common mineral on Earth; compose over 95% of the continental crust. Consist of combinations of a fundamental building block called silicon-oxygen tetrahedron, different groups: independent tetrahedra, single chains, double chains, sheet silicates, framework silicates.
Gem
a cut and finished stone ready to be used in jewelry. Examples - diamond, ruby, sapphire, emerald.
Facets
on a gem are the ground and polished surfaces made with a certain type of machine.
Cement
natural bond connecting rocks; mineral material that precipitates from water and fills the space between grains.
Clastic
type of sedimentary rock; rocks whose grains are stuck together by cement.
Crystalline
rocks whose crystals interlock with each other.
Bedrock
rock formations still attached to the Earth's crust.
Outcrop
an exposure of bedrock.
Grain sizes
equant, meaning that they have the same dimensions in all directions. Or inequant, meaning their dimensions are not the same in all directions.
Rock composition
refers to the proportions of different chemicals making up the rock, and thus the proportion chemicals affects the proportions of different minerals constituting the rock.
Rock texture
refers to the arrangement of grains in a rock; that is, the way the grains connect each other and whether inequant grains are aligned parallel to one another.
Rock layering
some rock bodies appear to contain distinct formations, defined either by bands of different compositions or textures, or by the alignment of inequant grains so that they trend parallel to one another.
Bedding
layering in sedimentary rocks.
Metamorphic foliation
layering in metamorphic rocks.
Volcano
a vent at which melt from inside the Earth spews onto the planet's surface. Erupt.
650-1100 degrees C
in degrees Celsius, the high temperatures at which igneous rocks freeze; the freezing of liquid melt to form solid igneous rock represents the same phenomenon as the freezing of water, except at much higher temperatures.
Intrusive igneous rock
rock made by the freezing of magma underground, after it has pushed its way (intruded) into preexisting rock of the crust.
Extrusive igneous rock
rocks that forms by the freezing of lava above ground, after it spills out (extrudes) onto the surface of the Earth and comes into contact with the atmosphere or ocean.
Pyroclastic debris
forms when clots of lava fly into the air in lava fountains and then freeze to form solid chunks before hitting the ground. Some forms when the explosion of a volcano shatters preexisting rock and ejects the fragments over the countryside.
Ash
a fine spray of lava instantly freezes to form fine particles of glass.
Reason for Earth's internal heat
The Earth radiated heat into space and slowly cooled. Eventually, the early formed sea of lava solidified and formed igneous rock. The cumulative effect of radioactivity has been sufficient to slow the cooling of the planet and subsequently allow for igneous rock to form.
Decompression
cause of melting; the variation in temperature with depth is expressed in the geotherm; because pressure prevents melting, a decrease in pressure can permit melting. Specifically, if the pressure affecting hot mantle rock decreases while the temperature remains unchanged, a magma forms.
Volatiles
cause of melting; magma can also form at locations where chemicals called volatiles mix with hot mantle rock. Elements such as water and carbon dioxide mix with hot rock, helping to break chemical bonds, so that if you add volatiles to a solid, hot, dry rock then it begins to melt. Volatiles essentially decrease a rock's melting temperature.
Heat transfer
cause of melting; when magma rises up from the mantle into the crust, it brings heat with it which raises the temperature of the surrounding crustal rock, and in some cases melting occurs.
Felsic
magma type; contains about 66% to 76% silica. Name reflects the occurrence of feldspar and quartz in rocks formed in this magma.
Intermediate
magma type; contains about 52% to 66% silica. Name indicates that these magmas have a composition between that of felsic and mafic magma.
Mafic
magma type; contains about 45% to 52% silica. Named because it produces rock containing abundant mafic minerals, magnesium and iron combinations.
Ultramafic
magma type; contains only about 38% to 45% silica. Extreme form of mafic magma.
Viscosity
the resistance to flow of magma. Reflects its distinct silica content, for silica tends to polymerize, meaning it links up to form long, chainlike molecules whose presence slows down the flowing ability of magma. Thus felsic magmas flow less easily than mafic magmas.
Source rock composition
distinguishing feature of magma; the composition of the melt reflects the composition of the solid from which it was derived. Not all magmas form from the same source rock, therefore not all magmas have the same compositions.
Partial melting
distinguishing feature of magma; Because not all minerals melt by the same amount under given conditions, and because chemical reactions take place during melting, the magma that forms as a rock begins to melt does not have the same composition as the original rock from which it was formed.The process where only part of a rock melts to form a magma.
Assimilation
distinguishing feature of magma; the process where magma sits in a magma chamber before completely solidifying, it may incorporate chemicals derived from the walls rocks of the chamber.
Magma mixing
distinguishing feature of magma; the process where different magmas formed in different locations from different sources may come in contact within a magma chamber prior to freezing. Thus the originally distinct magmas mix to create a new, different magma.
Fractional crystallization
distinguishing feature of magma; the process where magma changes composition as it cools because formation and sinking of crystals preferentially remove certain atoms from the magma.
Why magma rises
magma is less dense than surrounding rock, and thus is buoyant. Magma is less dense both because rock expands as it melts and because magma tends to contain smaller proportions of heavy elements. Also, magma rises because the weight of overlying rock creates a pressure at depth that squeezes it up.
Magma's speed of flow
Magma viscosity depends upon temperature, volatile content, and silica content. Hotter magma, more volatiles, and mafic magma all have less viscosity.
Dike
places where intrusive igneous rock creates tabular intrusions cutting across rock that does not have layering, this nearly vertical, wall-like tabular intrusions is formed. Cut across layering within the earth.
Sill
a nearly horizontal, tabletop-shaped tabular intrusion, parallel to layering within the earth.
Laccolith
an intrusion starting to inject between layers but then dome upwards, creating this blister-shaped intrusion.
Plutons
irregular or blob-shaped intrusions that range in size from tens of meters across to tens of kilometers across.
Batholiths
the intrusion of numerous plutons in a region, produces a vast composite body that may be several hundred kilometers long and over 100km wide; an immense body of igneous rock.
Stoping
a pluton formation theory; a process during which magma assimilates wall rock, and blocks of wall rock break off and sink into the magma.
Xenolith
if a stoped block does not melt entirely, but rather becomes surrounded by new igneous rock, it becomes this; xeno, meaning foreign.
Factors of magma cooling time
factors; the depth of the intrusion - the deeper, the more slowly it cools. The shape and size of a magma body - the greater the surface area, the faster it cools. The presence of circulating groundwater - water passing through cools magma faster.
Glassy igneous rocks
a rock made of solid mass of glass, or of tiny crystals surrounded by glass. Reflect light as glass does and tend to break conchoidally. Examples - obsidian, tachylite, pumice.
Crystalline igneous rocks
rocks that consist of mineral crystals that intergrow when the melt solidifies, interlocking structure. Examples - granite and rhyolite.
Fragmental igneous rocks
rocks with a fragmental texture consist of igneous fragments that are packed together, welded together, or cemented together after having solidified. Examples - pyroclastic rocks such as tuff or breccia.
Area of igneous activity
Four settings: in volcanic arcs bordering deep-ocean trenches, isolated hot spots, within continental rifts, and along mid-ocean ridges.
Hot-spot track
active hot-spot volcanoes commonly occur at the end of a chain of dead volcanoes.
Large Igneous Provinces (LIPs)
places with particularly voluminous quantities of magma erupting or intruding.
Superplumes
perhaps the cause for the large igneous provinces; formations within the mantle, plumes that bring up vastly more hot asthenosphere than normal plumes.
Flood basalts
hot basaltic lava that erupts with such low viscosity that it can flow tens to hundreds of kilometers across the landscape.
Rock-forming silicate minerals
the most important mineral group; comprise the most rock-forming minerals, they are very abundant due to large % of silicon and oxygen in Earth's crust. Examples - oxygen, silica, aluminum.
Weathering
refers to the processes that break up and corrode solid rock, eventually transforming it into sediment. Physical and chemical variations.
Physical weathering
breaks intact rocks into unconnected grains or chunks, collectively called debris or detritus. Grain size from largest to smallest: boulders, cobbles, pebbles, sand, silt, mud/clay.
Jointing
natural cracks that form in rocks due to removal of overburden or due to cooling.
Frost wedging
when water is trapped in a joint freezes, it forces the joint open and may cause the joint to grow.
Root wedging
tree roots that grow into joints can push those joints open in this process.
Salt wedging
process occurring in arid climates, dissolved salt in groundwater precipitates and grows as crystals in open pore spaces in rocks. This process pushes apart the surrounding grains and so weakens the rock that when exposed to wind or rain, the rock disintegrates into separate grains.
Thermal expansion
heat from an intense surface fire bakes and expands the outer layer of the rock. On cooling, the layer contracts, causing the outer part of the rock spall, or break off in sheet-like pieces.
Chemical weathering
refers to the chemical reactions that alter or destroy minerals when rock comes in contact with water solutions or air.
Saprolite
chemical weathering occurring in warm, wet climates can produce a layer of rotten rock, over 100km thick.
Dissolution
chemical weathering during which minerals dissolve into water.
Hydrolysis
during this process, water chemically reacts with minerals and breaks them down, working faster in slightly acidic water.
Oxidation
a reaction during which an element loses electrons, commonly takes place when elements combine with oxygen.
Hydration
the absorption of water into the crystal structure of minerals, causes some minerals to expand.
Differential weathering
when different rocks in an outcrop undergo weathering at different rates.
Soil
consists of rock and sediment that has been modified by physical and chemical interaction with organic material and rainwater, over time, to produce a substrate that can support the growth of plants.
Regolith
a name for any kind of unconsolidated debris that covers bedrock. Includes both soil and accumulations of sediment that have not evolved into soil.
Residual soil
type of soil; forms directly from underlying bedrock.
Transported soil
type of soil; forms from sediment that has been carried in from elsewhere. Include those formed from deposits left by rivers, glaciers, or wind.
Zone of leaching
contributes to formation of soil; occurs when rainwater percolates through the debris and carries dissolved ions and clay flakes downward, this is the region where the downward transport occurs.
Zone of accumulation
farther down from a zone of leaching, new mineral crystals precipitate directly out of the water or form when the water reacts with debris, this the region where the new minerals and clay collect.
Soil Horizons
Because different soil-forming processes operate at different depths, soils typically develop into these distinct zones. These zones can be arranged vertically into a soil profile.
O-horizon
highest soil horizon; consists almost entirely of organic matter and contains barely any mineral matter. Surface level has 'litter' and deeper it contains 'humus'. Part of the zone of leaching.
A-horizon
soil section below the O-horizon, humus has decayed further and has mixed with mineral grains (clay, silt, and sand). Water percolating through this horizon causes chemical weathering reactions to occur and produces ions in solution and new clay materials, carries soluble chemicals (iron, aluminum, carbonate) deeper into the subsurface. Part of the zone of leaching.
E-horizon
soil section below the A-horizon; a soil level that has undergone substantial leaching but has not yet mixed with organic material. Because it lacks organic materials, this horizon tends to be lighter than the A-horizon. Part of the zone of leaching.
B-horizon
subsoil, ions and clay leached and transported down from above accumulate here. As a result, new minerals form, and clay fills open spaces. Part of the zone of accumulation.
C-horizon
the base of the soil profile; consists of material derived from the substrate that's been chemically weathered and broken apart, but has not yet undergone leaching or accumulation.
Loam
a type of soil consisting of about 10-30% clay and the rest silt and sand. Pores remain between grains so that water and air can pass through and roots can easily penetrate.
Caliche
type of sedimentary soil/rock; Calcite in a pedocal soil accumulates in the B-horizon and may cement soil together, creating this solid mass.
Laterite
type of soil; forms in tropical regions where abundant rainfall drenches the land during the rainy season, and the soil dries during the dry season.
Soil erosion
the removal of soil by running water or by wind.
Clastic sedimentary rocks
sedimentary rock consisting of cemented together solid fragments and grains derived from preexisting rocks.
Biochemical sedimentary rocks
sedimentary rocks made up of the shells of organisms.
Organic sedimentary rocks
sedimentary rocks consisting of carbon-rich relicts of plants.
Chemical sedimentary rocks
sedimentary rocks made up of minerals that precipitate directly from water solutions.
Siliceous rocks
sedimentary rock composed of quartz.
Agrillaceous rocks
sedimentary rock composed of clay.
Carbonate rocks
sedimentary rock composed of calcite or dolomite.
Sandstone
Blocks of rock that are solid and durable but composed of rough quartz sand grains cemented together.
Five steps of clastic sedimentary rock formation
Weathering, erosion, transportation, deposition, and lithification.
Erosion
the combination of processes that separate rock or regolith from its substrate and carry it away. Involves abrasion, plucking, scouring, and dissolution, and is caused by air, water or ice.
Deposition
the process by which sediment settles out of the transporting medium.
Lithification
the transformation of loose sediment into solid rock.
Compaction
process that occurs after the sediment has been buried, pressure cause by the overburden squeezes out water and air that had been trapped between clasts, and the clasts press together tightly.
Cementation
process occurring after sediment has been compacted, can then be bounded together to make coherent sedimentary rock. Binding material consists of minerals (commonly quartz or calcite).
Factors classifying clastic sedimentary rocks
clast size, clast composition, angularity and sphericity, sorting, and character of cement.
Conglomerate
the burial and lithification of angular or rounded clasts form these types of rocks.
Arkose
type of rock; accumulated sand bars, within are mineral grains of quartz and feldspar, this sediment if buried and lithified.
Quartz sandstone
after sand has lost its feldspar composition due to weathering over time, sediment composed entirely of quartz grains gets buried and lithified to form this type of rock.
Siltstone and mudstone
when silt and clay accumulate in the flat areas bordering a stream, lagoon, or delta, the silt when lithified becomes this type of sediment. And the mud, when lithified, becomes another type of sediment, also known as shale.
Limestone
a type of carbonate rock; rocks formed from the calcite or aragonite skeletons of organisms form this biochemical sedimentary rock.
Chert
biochemical sedimentary rock; it's made from cryptocrystalline quartz. Examples - flint and jasper.
Coal
an organic sedimentary rock; black, combustible rock consisting of over 50% carbon.
Evaporites
chemical precipitates; salt deposits formed as a consequence of evaporation. Examples - rock salt and gypsum.
Travertine
inorganic limestone; rock composed of crystalline calcium carbonate formed by chemical precipitation.
Dolostone
forms from a chemical reaction between solid calcite and magnesium-bearing groundwater.
Sedimentary structure
the layering nature of sedimentary rocks, surface features of layers formed during deposition, and the arrangement of grains within layers.
Bed
a single layer of sediment or sedimentary rock with a recognizable top and bottom.
Strata
the boundary between two beds is a bedding plane; several beds constitute this structure.
Stratagraphic formation
a distinctive sequence of strata traced across a fairly large region. For example, a region may contain a succession of alternating sandstone and shale beds deposited by rivers, overlain by beds of marine limestone deposited later.
Ripples
relatively small, elongated ridges that form on a bed surface at right angles to the direction of the current flow of the rock.
Dunes
similar to ripples, but are much larger. Small ripples often form on the surface of these structures.
Cross beds
distinct internal laminations within a ripple or dune that are inclined at an angle to the boundary of the main sedimentary layer. Form as a consequence of the evolution of dunes or ripples.
Turbidity current
a submarine suspension of sediment.
Graded bed
a layer of sediment in which grain size varies from coarse at the bottom to fine at the top.
Turbidite
successive turbidity currents deposit successive graded beds, creating this sequence of strata.
Depositional environment
the conditions in which sediment was deposited. Examples - beach, glacial, and/or river environments.
Redbeds
a sedimentary bed that has developed a reddish color. The red comes from a film of iron oxide (hematite) that forms on grain surfaces.
Transgression
a process occurring when the sea level rises, the coast migrates inland. Through this, an extensive layer of beach forms.
Regression
a process occurring when sea level falls, the coast migrates seaward.
Diagenesis
a term used for all the physical, chemical, and biological processes that transform sediment into sedimentary rock and that alter characteristics of sedimentary rock one the rock has formed.
Light silicates
mineral group; feldspars, quartz, muscovite, clay minerals.
Dark Silicates
mineral group; olivine group, pyroxene group, amphibole group.
Granitic composition
type of igneous rock composition; composed of light-colored silicates, very rich in felsic (feldspar and silica). Major constituent of continental crust.
Basaltic composition
type of igneous rock composition; composed of dark silicates and calcium-rich feldspar, referred to as mafic (magnesium and iron). Make up the ocean floor/volcanic islands.
Granitic magma
type of magma; high silica content, viscous, liquid at temperatures as low as 700 degrees C.
Basaltic magma
type of magma; low in silica, fluid, crystallize at high temperatures.
Shield volcano
type of volcano; broad and slightly domed, primarily made of basaltic lava, large and erupt large volumes of lava. Form from either low viscosity basaltic lava or from large pyroclastic sheets.
Cinder cone
type of volcano; built from ejected lava fragments - cone shaped piles of tephra, steep slope angle, smaller in size, frequently occur in groups, deep craters.
Composite cone (stratovolcano)
type of volcano; most are adjacent to the Pacific, larger in size, interbedded lavas and pyroclastics, consist of alternating layers of lava and tephra, most violent type of activity, may produce nuee ardente or lahars.
Calderas
volcanic landform; steep walled depression at the summit, size exceeds one kilometer in diameter.
Pyroclastic flows
lava flow; associated with felsic magma, consists of ash and pumice fragments, material is propelled from the vent at a high speed.
Fissure eruptions/lava plateaus
fluid basaltic lava extruded from crustal fractures called fissures.
Lava domes
volcanic landform; bulbous mass of congealed lava, associated with explosive eruptions of gas-rich magma.
Volcanic pipes/necks
volcanic landform; pipes are short conduits that connect a magma chamber to the surface.
Subsidence
a reference to the sinking of the lithosphere; allows for sediment to accumulate in regions where this occurs.
Sedimentary Basins
a sediment-filled depression; in an area where the lithosphere has subsided.
Geothermal gradient
the rate of increase in temperature, decreases with increasing depth. The dashed lines represent the solidus and liquidus for mantle rock (peridotite). The solidus line defines the conditions of pressure and temperature at which mantle rock begins to melt. Values to the left of the solidus indicate pressures and temperatures for which rock stays entirely solid. The liquidus represents conditions at which all solid disappears and only melt remains.
Basaltic lava flows
type of lava flow; mafic, low viscosity, extremely hot, flows very quickly.
Lava tube
an insulated, tunnel-like conduit through which lava moves within a flow.
pahoehoe
type of lava flow; a lava flow with warm, pasty surfaces wrinkling into smooth, glassy, rope-like bridges.
a'a'
type of lava flow; surface layer of the lava freezes and then breaks up due to the continued movement of lava underneath, becomes a jumble of sharp, angular fragments, yielding a rubbly flow.
Columnar jointing
during the final stages of cooling, lava flows contract and may fracture into roughly hexagonal columns.
Andesitic lava flows
type of lava flow; higher silica content, greater viscosity, forms a large mound above the vent out of a volcano.
Rhyolitic lava flows
type of lava flow; the most viscous of any lava flow because it is the most silicic and the coolest in nature. Tends to accumulate in a lava dome above the vent or in short and bulbous flows 1 to 2 km long.
Lapilli
pea to plum-sized fragments of pyroclastic debris, consists of pumice or scoria fragments.
Volcanic blocks/bombs
coarse pyroclastic debris, apple to refrigerator-sized fragments. Chunks of preexisting igneous rock or large lava blobs which discharge from volcanic eruptions.
Tuff
built up deposit of volcanic bombs and lapilli, known as volcanic agglomerate.
Tephra
unconsolidated deposits of pyroclastic grains, regardless of size, that have been erupted from a volcano constitute these pyroclastic deposits.
Ignimbrite
a sheet of tuff formed from a pyroclastic flow.
Effusive eruptions
type of volcanic eruption; produce mainly lava flows, yield low-viscosity basaltic lavas.
Explosive eruptions
type of volcanic eruption; pyroclastic, produce clouds and avalanches of pyroclastic debris. Gas expands in the rising magma, cannot escape. The pressure becomes so great that it blasts the lava, and volcanic rock, out of the volcano.
Phreatomagmatic eruptions
type of volcanic eruption; takes place when water gains access to the hot rock around the magma chamber and suddenly transforms into steam, a pyroclastic eruption involving the reaction of water with magma.
The effect of viscosity on eruptive style
low-viscosity (basaltic) lava flows out of a volcano easily, whereas high-viscosity (andesitic and rhyolitic) lava can clog and build pressure within a volcano. Basaltic eruptions are typically effusive and produce shield volcanoes, whereas rhyolitic eruptions are explosive.
The effect of gas pressure on eruptive style
the injection of magma within the magma chamber and conduit generates an outward pressure within the volcano. The presence of gas within the magma increases this pressure, as gas expands greatly as it rises toward the Earth's surface. Rhyolitic and andesitic magmas contain more gas, and thus eruptions of these magmas are more explosive that are eruptions of basaltic magma.
The effect of the environment on eruptive style
lava flowing on dry land cools more slowly that lava erupting underwater.