provides the capacity to do work, to cause something to happen, or to cause change in a system.
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.
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.
organic shale is referred to as ____ ___. Contains the raw materials from which hydrocarbons eventually form. These rocks are always sedimentary.
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.
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.
a known supply of oil and gas held underground. Currently countries bordering the Persian Gulf contain the world's largest reserves.
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 ____ ___.
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 ..
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.
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.
in some cases, groundwater passing through rock dissolves minerals and creates space, this refers to the amount of open space in a rock.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 ___ ___.
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..
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.
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)
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.
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.
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.
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 __ ___.
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.
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.
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 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.
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.
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.
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 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.
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..
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.
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.
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 farms have been established around to world to generate electricity. The electricity is clean, but wind production requires the construction of large, noisy towers.
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.
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.
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.
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 ___.
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 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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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 ____ ____.
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 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.
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.
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.
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.
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.
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.
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.
mine below the surface of the Earth; , best mining technique for deeper deposits in horizontal layers, more than about 100 meters below.
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.
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.
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.
from sandstone, beaches, or riverbeds; quartz sand is used for construction and for making glass
occurs either as native sulfur, typically above salt domes, or in sulfide minerals; used for fertilizer and chemicals
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.
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.
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.
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).
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.
Slow, downslope flow of water-saturated materials common to permafrost or tundra (cold, treeless ragions) areas.
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.
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.
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.
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.
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.
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.
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.
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.
these happen when large blocks of rock break loose from a cliff face, or steep slope, along a joint and start tumbling.
Type of slope failure that occurs when a mixture of soil, regolith, and rocks becomes dislodged and falls down the slope.
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.
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.
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.
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.
The process by which an earthquake's violent movement suddenly turns loose soil into liquid mud.
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.
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.
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.
geologists use this term for any channelized body of running water, meaning water that flows along a channel, an elongate depression or trough.
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.
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.
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.
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.
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.
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)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
type of stream erosion; running dissolves soluble minerals as it passes, and carries the minerals away in solution.
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 ___ ___.
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.
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.
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.
the ___ of a stream refers to the total quantity of sediment it can carry. Depends upon its competence and discharge.
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'.
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.
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.
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.
forms when the gradients of a stream becomes so steep that the water literally free-falls down the stream bed.
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 ___ __.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
..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.
the region where the land meets the sea, and where over 60% of the global population lives today.
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.
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.
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.
at many locations, relatively narrow and deep valleys called ____ ___ dissect continental shelves and slopes.
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.
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 ____.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Depth below the wave crest at which water movement associated with the wave becomes negligible; about half the wave length.
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.
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'
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.
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 ___ __.
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.
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.
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.
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.
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.
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.
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.
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 ___ ___.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
sediment or rocks that do not transmit water easily and therefore retard the motion of water.
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.
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.
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.
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.
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.
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.
___ 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.
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..
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.