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GEOLOGY 102

GEOLOGY 102 - "ESSENTIALS OF GEOLOGY: THIRD EDITION" UNIVERSITY OF OREGON
STUDY
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asteroid
One of many millions of small, rocky, and/or metallic objects that orbit the Sun, consisting of fragments of once-larger planetesimals, or chunks of protoplanetary material; most lie in the region between Mars and Jupiter.
asthenosphere
The layer of the mantle that lies between 100-150 km and 350 km deep; the asthenosphere is relatively soft and can flow when acted on by force.
atmosphere
A layer of gases that surrounds a planet.
bathymetry
Variation in depth.
big bang
A cataclysmic explosion that scientists suggest represents the formation of the Universe; before this event, all matter and all energy were packed into one volumeless point.
comet
A ball of ice and dust, probably remaining from the formation of the Solar System, that orbits the Sun.
core
The dense, iron-rich center of the Earth.
cosmology
The study of the overall structure of the Universe.
crust
The rock that makes up the outermost layer of the Earth.
differentiation
In the context of planet formation, the process by which a planet separates into a metallic core and a rocky mantle very early in its history.
earthquake
A vibration caused by the sudden breaking or frictional sliding of rock in the Earth.
Earth System
The global interconnecting web of physical and biological phenomena involving the solid Earth, the hydrosphere, and the atmosphere.
expanding Universe theory
The theory that the whole Universe must be expanding because galaxies in every direction seem to be moving away from us.
fault
A fracture on which one body of rock slides past another.
galaxy
An immense system of hundreds of billions of stars.
gas-giant planet
The outer planets (Jupiter, Saturn, Uranus, Neptune) that are very large and consist mostly of volatile elements.
geothermal gradient
The rate of change in temperature with depth.
glass
A solid in which atoms are not arranged in an orderly pattern.
groundwater
Water that resides under the surface of the Earth, mostly in pores or cracks of rock or sediment.
lithosphere
The relatively rigid, non-flowable, outer 100- to 150-km-thick layer of the Earth; constituting the crust and the top part of the mantle.
lower mantle
The deepest section of the mantle, stretching from 670 km down to the core-mantle boundary.
magnetic field
The region affected by the force emanating from a magnet.
mantle
The thick layer of rock below the EarthÕs crust and above the core.
Melt
Molten (liquid) rock.
metal
A solid composed almost entirely of atoms of metallic elements; it is generally opaque, shiny, smooth, and malleable, and can conduct electricity.
meteor
An object that has entered a planetÕs atmosphere and is glowing and evaporating as it streaks to the planetÕs surface.
Meteorite
A piece of rock or metal alloy that fell from space and landed on Earth.
Mineral
A homogenous, naturally occurring, solid inorganic substance with a definable chemical composition and an internal structure characterized by an orderly arrangement of atoms, ions, or molecules in a lattice. Most minerals are inorganic.
Moho
The seismic-velocity discontinuity that defines the boundary between the EarthÕs crust and mantle.
moon
A solid object of ice and/or rock and metal that orbits a planet.
nebula
A cloud of gas or dust in space.
nebula theory
The concept that planets grow out of rings of gas, dust, and ice surrounding a new-born star.
organic chemical
A carbon-containing compound that occurs in living organisms, or that resembles such compounds; it consists of carbon atoms bonded to hydrogen atoms along with varying amounts of oxygen, nitrogen, and other chemicals.
planet
A relatively large, spherical object that orbits a star and has cleared its orbit of most debris.
planetesimal
Tiny, solid pieces of rock and metal that collect in a planetary nebula and eventually accumulate to form a planet.
protoplanet
A body that grows by the accumulation of planetesimals but has not yet become big enough to be called a planet.
protoplanetary disk
The flattened cloud of dust, gas, and ice that orbits a nascent star prior to the formation of planets.
protostar
A dense body of gas that is collapsing inward because of gravitational forces and that may eventually become a star.
red shift
The phenomenon in which a source of light moving away from you very rapidly shifts to a lower frequency; that is, toward the red end of the spectrum.
rock
A coherent, naturally occurring solid, consisting of an aggregate of minerals or a mass of glass.
sediment
An accumulation of loose mineral grains, such as boulders, pebbles, sand, silt, or mud, that are not cemented together.
Solar System
The Sun and all the objects that orbit it (including planets, moons, comets, and asteroids).
star
A large sphere, composed dominantly of hydrogen and helium, in which fusion reactions are producing energy.
stellar wind
Particles that have been ejected from a star and are shooting through space.
supernova
A short-lived, very bright object in space that results from the cataclysmic explosion marking the death of a very large star; the explosion ejects large quantities of matter into space to form new nebulae.
topography
Variations in elevation.
transition zone
The middle portion of the mantle, from 400 to 670 km deep, in which there are several jumps in seismic velocity.
Universe
The sum of all matter and energy making up the hundreds of billions of known galaxies.
upper mantle
The uppermost section of the mantle, reaching down to a depth of 400 km.
vacuum
Space that contains very little matter in a given volume (e.g., a region in which air has been removed).
wave
A means of transmitting energy from one location to another; waves can be vibrations that propagate through a material, or undulations of electromagnetic fields that can propagate either through a material or in a vacuum.
wavelength
The horizontal difference between two adjacent wave troughs or two adjacent crests.
absolute plate velocity
The movement of a plate relative to a fixed point in the mantle.
abyssal plain
A broad, relatively fl at region of the ocean that lies at least 4.5 km below sea level.
active continental margin
A continental margin that coincides with a plate boundary.
apparent polar-wander path
A path on the globe along which a magnetic pole appears to have wandered over time; in fact, the continents drift, while the magnetic pole stays fairly fixed.
asthenosphere
The layer of the mantle that lies between 100-150 km and 350 km deep; the asthenosphere is relatively soft and can flow when acted on by force.
black smoker
The cloud of suspended minerals formed where hot water spews out of a vent along a mid-ocean ridge; the dissolved sulfide components of the hot water instantly precipitate when the water mixes with seawater and cools.
collision
The process of two buoyant pieces of lithosphere converging and squashing together.
continental drift hypothesis
The idea that continents have moved and are still moving slowly across the Earth's surface.
continental rift
A linear belt along which continental lithosphere stretches and pulls apart.
convergent plate boundary
A boundary at which two plates move toward each other so that one plate sinks (subducts) beneath the other; only oceanic lithosphere can subduct.
divergent plate boundary
A boundary at which two lithosphere plates move apart from each other; they are marked by mid-ocean ridges.
fracture zone
A narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to a mid-ocean ridge, and the actively slipping part of a fracture zone is a transform fault.
global positioning system (GPS)
A satellite system people can use to measure rates of movement of the Earth's crust relative to one another, or simply to locate their position on the Earth's surface.
hot spot
A location at the base of the lithosphere, at the top of a mantle plume, where temperatures can cause melting.
hot-spot track
A chain of now-dead volcanoes transported off the hot spot by the movement of a lithosphere plate.
lithosphere
The relatively rigid, nonflowable, outer 100- to 150-km-thick layer of the Earth; constituting the crust and the top part of the mantle.
lithosphere plate
A portion of the outer, relatively rigid layer of the Earth; most seismic activity happens at the boundaries of plates, while the interior of a plate is relatively stable.
magnetic anomaly
The difference between the expected strength of the Earth's magnetic field at a certain location and the actual measured strength of the field at that location.
magnetic declination
The angle between the direction a compass needle points at a given location and the direction of true north.
magnetic dipole
A magnetic entity that has a north and south end.
magnetic inclination
The angle between a magnetic needle free to pivot on a horizontal axis and a horizontal plane parallel to the Earth's surface.
magnetic pole
The north or south ends of a magnet; field lines point straight down at the pole.
magnetic reversal
The change of the Earth's magnetic polarity; when a reversal occurs, the field flips from normal to reversed polarity, or vice versa.
magnetic-reversal chronology
The history of magnetic reversals through geologic time.
mantle plume
A column of very hot rock rising up through the mantle.
marine magnetic anomaly
An unusually strong or unusually weak magnetic field, as measured over the sea floor; in map view, they look like stripes that are parallel to the mid-ocean ridge.
mid-ocean ridge
A 2-km-high submarine mountain belt that forms along a divergent oceanic plate boundary.
paleomagnetism
The record of ancient magnetism preserved in rock.
paleopole
The supposed position of the Earth's magnetic pole in the past, with respect to a particular continent.
Pangaea
A supercontinent that assembled at the end of the Paleozoic Era.
passive margin basin
A thick accumulation of sediment along a tectonically inactive coast, formed over crust that stretched and thinned when the margin first began.
plate
One of about twenty distinct pieces of the relatively rigid lithosphere.
plate boundary
The border between two adjacent lithosphere plates.
relative plate velocity
The movement of one lithosphere plate with respect to another.
ridge-push force
The force that drives plates away from a mid-ocean ridge; it is caused by the fact that the ridge is elevated relative to the regions of oceanic plate away from the ridge.
rifting
The process by which continental lithosphere stretches and breaks apart; rifting produces normal faults and, commonly, volcanism.
sea-floor spreading
The gradual widening of an ocean basin as new oceanic crust forms at a mid-ocean ridge axis and then moves away from the axis.
seamount
An isolated submarine mountain.
slab-pull force
The force that downgoing plates (or slabs) apply to oceanic lithosphere at a convergent margin.
subduction
The process by which one oceanic plate bends and sinks down into the asthenosphere beneath another plate.
transform plate boundary
A boundary at which one lithosphere plate slips laterally past another.
trench
A deep elongate trough bordering a volcanic arc; a trench defines the trace of a convergent plate boundary.
triple junction
A point where three lithosphere plate boundaries intersect.
volcanic arc
A curving chain of active volcanoes formed adjacent to a convergent plate boundary.
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.
carbonate rocks
Rocks containing calcite and/or dolomite.
cleavage
(1) The tendency of a mineral to break along preferred planes; (2) a type of foliation in low-grade metamorphic rock.
conchoidal fracture
Smoothly curving, clamshell-shaped surfaces along which materials with no cleavage planes tend to break.
Crystal
A single, continuous piece of a mineral bounded by flat surfaces that formed naturally as the mineral grew.
crystal face
The flat surface of an euhedral mineral grain.
crystal habit
The general shape of a crystal or cluster of crystals that grew unimpeded.
crystal lattice
The orderly framework within which the atoms or ions of a mineral are fixed.
crystal structure
The internal arrangement of atoms or ions within a crystal.
facet
The flat surface of a cut gemstone; facets are produced by grinding.
gem
A mineral or form of a mineral that is particularly beautiful and/or rare, and thus has value.
geode
A cavity in which euhedral crystals precipitate out of water solutions passing through a rock.
hardness
In mineralogy, hardness refers to the resistance of a mineral to scratching; a harder mineral can scratch a softer mineral.
Luster
The way a mineral surface scatters light.
mineral
A homogenous, naturally occurring, solid inorganic substance with a definable chemical composition and an internal structure characterized by an orderly arrangement of atoms, ions, or molecules in a lattice. Most minerals are inorganic.
mineralogy
The study of minerals.
Mohs hardness scale
A list of ten minerals in a sequence of relative hardness, with which other minerals can be compared.
polymorph
Two minerals that have the same chemical composition but a different crystal lattice structure.
Silicate minerals
Minerals composed of silicon-oxygen tetrahedra linked in various arrangements; most contain other elements as well.
silicon-oxygen tetrahedron
The basic building block of silicate minerals; it consists of one silicon atom surrounded by four oxygen atoms.
specific gravity
A number representing 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.
streak
The color of the powder produced by pulverizing a mineral on an unglazed ceramic plate.
symmetry
The condition in which the shape of one part of an object is a mirror image of the other part.
assimilation
The process of magma contamination in which blocks of wall rock fall into a magma chamber and dissolve.
batholith
A vast composite, intrusive, igneous rock body up to several hundred kilometers long and 100 km wide, formed by the intrusion of numerous plutons in the same region.
Bowen's reaction series
The sequence in which different silicate minerals crystallize during the progressive cooling of a melt.
crystalline igneous rock
A rock that solidifies from a melt and consists of interlocking crystals.
dike
A tabular (wall-shaped) intrusion of rock that cuts across the layering of country rock.
extrusive igneous rock
Rock that forms by the freezing of lava above ground, after it flows or explodes out (extrudes) onto the surface and comes into contact with the atmosphere or ocean.
fractional crystallization
The process by which magma becomes progressively more silicic as it cools, because early-formed crystals settle out.
fragmental igneous rock
Fragments of igneous material that have been stuck together to form a coherent mass.
Geotherm
The change in temperature with depth in the Earth.
glassy igneous rock
Igneous rock consisting entirely of glass, or of tiny crystals surrounded by a glass matrix.
igneous rock
Rock that forms when hot molten rock (magma or lava) cools and freezes solid.
intrusive igneous rock
Rock formed by the freezing of magma underground.
Laccolith
A shallow igneous intrusion that has a blister-like shape.
lava
Molten rock that has flowed out onto the EarthÕs surface.
lava flow
Sheets or mounds of lava that flow onto the ground surface or sea floor in molten form and then solidify.
Magma
Molten rock beneath the EarthÕs surface.
obsidian
An igneous rock consisting of a solid mass of volcanic glass.
partial melting
The melting in a rock of the minerals with the lowest melting temperatures, while other minerals remain solid.
Pegmatite
A coarse-grained igneous rock containing crystals of up to tens of centimeters across and occurring in dike-shaped intrusions.
pluton
An irregular or blob-shaped intrusion; can range in size from tens of meters across to tens of kilometers across.
pumice
A glassy igneous rock that forms from felsic frothy lava and contains abundant (over 50%) pore space.
pyroclastic rock
Rock made from fragments blown out of a volcano during an explosion that were then packed or welded together.
scoria
A glassy mafic igneous rock containing abundant air-filled holes.
sill
A nearly horizontal table-top-shaped tabular intrusion that occurs between the layers of country rock.
Stoping
A process by which magma intrudes; blocks of wall rock break off and then sink into the magma.
Tuff
A pyroclastic igneous rock composed of volcanic ash and fragmented pumice, formed when accumulations of the debris cement together.
vesicle
Open holes in igneous rock formed by the preservation of bubbles in magma as the magma cools into solid rock.
volcanic ash
Tiny glass shards formed when a fine spray of exploded lava freezes instantly upon contact with the atmosphere.
volcanic breccias
A rock composed of angular chunks of volcanic debris that have been cemented together.
volcano
(1) A vent from which melt from inside the Earth spews out onto the planetÕs surface; (2) a mountain formed by the accumulation of extrusive volcanic rock.
xenolith
A relict of wall rock surrounded by intrusive rock when the intrusive rock freezes.
a'a'
A lava flow with a rubbly surface.
active volcano
A volcano that has erupted within the past few centuries and will likely erupt again.
ash fall
Ash that falls to the ground out of an ash cloud.
block
In the context of igneous materials, a block is a chunk of igneous rock blasted out of a volcano.
bombs
A frozen blob of rock formed when magma ejected from a volcano freezes in flight; bombs are typically streamlined.
caldera
A large circular depression with steep walls and a fairly flat floor, formed after an eruption as the center of the volcano collapses into the drained magma chamber below.
cinder cone
A subaerial volcano consisting of a cone-shaped pile of tephra whose slope approaches the angle of repose for tephra.
columnar jointing
A type of fracturing that yields roughly hexagonal columns of basalt; columnar joints form when a dike, sill, or lava flow cools.
Crater
(1) A circular depression at the top of a volcanic mound; (2) a depression formed by the impact of a meteorite.
dormant volcano
A volcano that has not erupted for hundreds to thousands of years but does have the potential to erupt again in the future.
effusive eruption
An eruption that yields mostly lava, not ash.
explosive eruption
Violent volcanic eruption that produces clouds and avalanches of pyroclastic debris.
extinct volcano
A volcano that was active in the past but has now shut off entirely and will not erupt in the future.
fissure track
A line of damage formed in the crystal lattice of a mineral by the impact of an atomic particle ejected during the decay of a radioactive isotope.
flood basalt
Vast sheets of basalt that spread from a volcanic vent over an extensive surface of land; they may form where a rift develops above a continental hot spot, and where lava is particularly hot and has low viscosity.
ignimbrite
Rock formed when deposits of pyroclactic flows solidify.
lahar
A thick slurry formed when volcanic ash and debris mix with water, either in rivers or from rain or melting snow and ice on the flank of a volcano.
lapilli
Marble-to-plum-sized fragments of pyroclastic debris.
lava tube
The empty space left when a lava tunnel drains; this happens when the surface of a lava flow solidifies while the inner part of the flow continues to stream downslope.
magma chamber
A space below ground filled with magma.
pahoehoe
A lava flow with a surface texture of smooth, glassy, rope-like ridges.
pyroclastic debris
Fragmented material that sprayed out of a volcano and landed on the ground or sea floor in solid form.
pyroclastic flow
A fast-moving avalanche that occurs when hot volcanic ash and debris mix with air and flow down the side of a volcano.
shield volcano
A subaerial volcano with a broad, gentle dome, formed either from low-viscosity basaltic lava or from large pyroclastic sheets.
stratovolcano
A large, cone-shaped subaerial volcano consisting of alternating layers of lava and tephra.
tephra
Unconsolidated accumulations of pyroclastic grains.
tuff
A pyroclastic igneous rock composed of volcanic ash and fragmented pumice, formed when accumulations of the debris cement together.
vesicles
Open holes in igneous rock formed by the preservation of bubbles in magma as the magma cools into solid rock.
volcanic debris flow
A mixture of water and clasts of volcanic material that moves down the slope of a volcano.
volcaniclastic deposit
A layer composed of fragments of igneous material (e.g., tephra, ash, bombs) erupted from volcanoes.
volcano
(1) A vent from which melt from inside the Earth spews out onto the planet's surface; (2) a mountain formed by the accumulation of extrusive volcanic rock.
arkose
A clastic sedimentary rock composed of sand-sized grains that include quartz and feldspar.
bed
A distinct layer of sedimentary strata.
biochemical sedimentary rock
Sedimentary rock formed from material (such as shells) produced by living organisms.
breccia
Coarse sedimentary rock consisting of angular fragments; or rock broken into angular fragments by faulting.
Cementation
The phase of lithification in which cement, consisting of minerals that precipitate from groundwater, partially or completely fills the spaces between clasts and attaches each grain to its neighbor.
chemical sedimentary rock
Sedimentary rock made up of minerals that precipitate directly from water solution.
clastic sedimentary rock
Sedimentary rock consisting of cemented-together detritus derived from the weathering of preexisting rock.
Clasts
A fragment of detritus (e.g., a sand grain or a pebble).
Conglomerate
Very coarse-grained sedimentary rock consisting of rounded clasts.
cross bed
A lamination inclined to the main bedding; it represents the slip face of a layer deposited in a current.
Deposition
The process by which sediment settles out of a transporting medium.
diagenesis
Changes that happen to sediment or sedimentary rock during and subsequent to lithification but at temperatures less than that of the lowest grade metamorphism.
dolostone
A type of carbonate sedimentary rock that contains significant quantities of dolomite.
erosion
The grinding away and removal of Earth's surface materials by moving water, air, or ice.
graded bed
A layer of clastic sediment or sedimentary rock in which clast size progressively decreases from the base to the top of the bed; graded beds form by deposition from a turbidity current.
Limestone
Sedimentary rock composed of calcite.
lithification
The transformation of loose sediment into solid rock through compaction and cementation.
mudstone
Very fine-grained sedimentary rock that will not easily split into sheets.
organic sedimentary rock
Sedimentary rock (such as coal) formed from carbon-rich relicts of organisms.
regression
The seaward migration of a shoreline caused by a lowering of sea level.
ripple marks
Wave-like ridges and troughs on the surface of a sedimentary layer formed during deposition in a current.
Sandstone
Coarse-grained sedimentary rock consisting almost entirely of quartz.
sedimentary basin
A depression, created as a consequence of subsidence, that fills with sediment.
sedimentary rock
Rock that forms either by the cementing together of fragments broken off preexisting rock or by the precipitation of mineral crystals out of water solutions at or near the EarthÕs surface.
sedimentary structure
A characteristic of sedimentary deposits that pertains to the character of bedding and/or the surface features of a bed.
shale
Very fine-grained sedimentary rock that breaks into thin sheets.
siltstone
Fine-grained sedimentary rock generally composed of very small quartz grains.
Sorting
(1) The range of clast sizes in a collection of sediment; (2) the degree to which sediment has been separated by flowing currents into different-size fractions.
strata
A succession of sedimentary beds.
stratigraphic formation
A recognizable layer of a specific sedimentary rock type or set of rock types, deposited during a certain time interval, that can be traced over a broad region.
Subsidence
The vertical sinking of the EarthÕs surface in a region, relative to a reference plane.
transgression
The inland migration of shoreline resulting from a rise in sea level.
travertine
A carbonate rock formed by precipitation of carbonate minerals from water at springs or on the surface of caves.
turbidity current
A submarine avalanche of sediment and water that speeds down a submarine slope.
burial metamorphism
Metamorphism due to the increase in temperature and pressure in a rock when it has been buried to a depth of several kilometers.
contact metamorphism
Metamorphism caused by heat conducted into country rock from an igneous intrusion.
differential stress
A condition causing a material to experience a push or pull in one direction of a greater magnitude than the push or pull in another direction; in some cases, differential stress can result in shearing.
dynamic metamorphism
Metamorphism that occurs as a consequence of shearing alone, with no change in temperature or pressure.
Dynamothermal metamorphism
Metamorphism that involves heat, pressure, and shearing.
Exhumation
The process (involving uplift and erosion) that returns deeply buried rocks to the surface.
foliation
Layering formed as a consequence of the alignment of mineral grains, or of compositional banding in a metamorphic rock.
Gneiss
A compositionally banded metamorphic rock typically composed of alternating dark- and light-colored layers.
Hornfels
Rock that undergoes metamorphism simply because of a change in temperature, without being subjected to differential stress.
hydrothermal metamorphism
The change that occurs in a rock due to interaction with high-temperature water solutions.
Marble
A metamorphic rock composed of calcite and transformed from a protolith of limestone.
metaconglomerate
Conglomerate that has undergone metamorphism, but in which clasts are still recognizable; typically the clasts are stretched or flattened.
metamorphic aureole
The region around a pluton, stretching tens to hundreds of meters out, in which heat transferred into the country rock and metamorphosed the country rock.
metamorphic facies
A set of metamorphic mineral assemblages indicative of metamorphism under a specific range of pressures and temperatures.
metamorphic foliation
A fabric defined by parallel surfaces or layers that develop in a rock as a result of metamorphism; schistocity and gneissic layering are examples.
metamorphic grade
An informal designation of the degree to which a rock has undergone metamorphism; high-grade rocks have endured higher temperatures than low-grade rocks.
metamorphic mineral
A mineral formed by solid-state transitions under metamorphic conditions.
metamorphic rock
Rock that forms when preexisting rock changes into new rock as a result of an increase in pressure and temperature and/or shearing under elevated temperatures; metamorphism occurs without the rock first becoming a melt or a sediment.
metamorphic texture
The arrangement of grains (e.g., preferred orientation) formed as a result of metamorphism.
metamorphic zone
The region between two metamorphic isograds, typically named after an index mineral found within the region.
Metamorphism
The process by which one kind of rock transforms into a different kind of rock.
Metasomatism
The process by which a rocks overall chemical composition changes during metamorphism because of reactions with hot water that bring in or remove elements.
phyllite
A fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained mica.
preferred mineral orientation
The metamorphic texture that exists where platy grains lie parallel to one another and/or elongate grains align in the same direction.
protolith
The original rock from which a metamorphic rock formed.
quartzite
A metamorphic rock composed of quartz and transformed from a protolith of quartz sandstone.
regional metamorphism
Metamorphism of a broad region, usually the result of deep burial during an orogeny.
schist
A medium- to coarse-grained metamorphic rock that possesses schistosity.
shield
An older, interior region of a continent.
shock metamorphism
Solid-state changes in rock that result from the extreme pressure accompanying a meteorite impact.
slate
Fine-grained, low-grade metamorphic rock, formed by the metamorphism of shale.
thermal metamorphism
Metamorphism caused by heat conducted into country rock from an igneous intrusion.
aftershocks
The series of smaller earthquakes that follow a major earthquake.
body waves
Seismic waves that pass through the interior of the Earth.
compressional waves
Waves in which particles of material move back and forth parallel to the direction in which the wave itself moves.
Displacement
The amount of movement or slip across a fault plane.
earthquake
A vibration caused by the sudden breaking or frictional sliding of rock in the Earth.
elastic-rebound theory
The concept that earthquakes occur when rock elastically bends until it fractures; the fracturing generates earthquake energy and decreases the elastic energy stored in the rock.
epicenter
The point on the surface of the Earth directly above the focus of an earthquake.
fault
A fracture on which one body of rock slides past another.
fault scarp
A small step on the ground surface where one side of a fault has moved vertically with respect to the other.
Foreshocks
The series of smaller earthquakes that precede a major earthquake.
hypocenter
The point below the Earth's surface where the energy is produced during an earthquake.
intraplate earthquake
Earthquake that occurs away from plate boundaries.
Liquefaction
The transformation of seemingly solid sediment into a liquid-like slurry, in response to ground shaking.
Magnitude
Any numerical representation of the size of an earthquake as determined by measuring the amplitude of ground motion.
Mercalli intensity scale
An earthquake characterization scale based on the amount of damage that the earthquake causes.
moment-magnitude scale
A numerical representation of the size of an earthquake that takes into account the area of the fault that slipped, the amount of slip, and the strength of the rock that broke.
recurrence interval
The average time between successive geologic events.
Richter scale
A scale that defines earthquakes on the basis of the amplitude of the largest ground motion recorded on a seismogram.
seismic belt
The relatively narrow strips of crust on Earth under which most earthquakes occur.
Seismicity
Earthquake activity.
seismic waves
Waves of energy emitted at the focus of an earthquake.
Seismogram
The record of an earthquake produced by a seismograph.
Seismograph
An instrument that can record the ground motion from an earthquake.
shear waves
Seismic waves in which particles of material move back and forth perpendicular to the direction in which the wave itself moves.
stick-slip behavior
Stop-start movement along a fault plane caused by friction, which prevents movement until stress builds up sufficiently.
surface waves
Seismic waves that travel along the Earth's surface.
Tsunami
A large wave along the sea surface triggered by an earthquake or large submarine slump.
Wadati-Benioff zone
A sloping band of seismicity defined by intermediate- and deep-focus earthquakes that occur in the down-going slab of a convergent plate boundary.
anticline
A fold with an arch-like shape in which the limbs dip away from the hinge.
axial surface
In the context of folds, this is the imaginary plane that contains the hinge lines of successive layers in the fold; it is the surface that divides a fold into its two separate limbs.
basin
A fold or depression shaped like a right-side-up bowl.
brittle deformation
The cracking and fracturing of a material subjected to stress.
Compression
A push or squeezing felt by a body.
craton
A long-lived block of durable continental crust commonly found in the stable interior of a continent.
Deformation
A change in the shape, position, or orientation of a material, by bending, breaking, or flowing.
dip
The angle at which a layer tilts, relative to horizontal; the angle is measured in an imaginary vertical plane that trends perpendicular to the strike.
Displacement
The amount of movement or slip across a fault plane.
Dome
Folded or arched layers with the shape of an overturned bowl.
ductile deformation
The bending and flowing of a material (without cracking and breaking) subjected to stress.
Fault
A fracture on which one body of rock slides past another.
fault scarp
A small step on the ground surface where one side of a fault has moved vertically with respect to the other.
fold
A bend or wrinkle of rock layers or foliation; folds form as a consequence of ductile deformation.
foliation
Layering formed as a consequence of the alignment of mineral grains, or of compositional banding in a metamorphic rock.
global positioning system (GPS)
A satellite system people can use to measure rates of movement of the Earth's crust relative to one another, or simply to locate their position on the Earth's surface.
Hinge
The portion of a fold where curvature is greatest.
isostasy
The condition that exists when the buoyancy force pushing lithosphere up equals the gravitational force pulling lithosphere down.
joints
Naturally formed cracks in rocks.
limb (of fold)
The side of a fold, showing less curvature than at the hinge.
monocline
A fold in the land surface whose shape resembles that of a carpet draped over a stair step.
normal fault
A fault in which the hanging-wall block moves down the slope of the fault.
orogenic collapse
The process in which mountains begin to collapse under their own weight and spread out laterally.
orogen
A linear range of mountains.
orogeny
A mountain-building event.
pressure
Force per unit area, or the ÒpushÓ acting on a material in cases where the push is the same in all directions.
reverse fault
A steeply dipping fault on which the hanging-wall block slides up.
shear stress
A stress that moves one part of a material sideways past another part.
strain
The change in shape of an object in response to deformation (i.e., as a result of the application of a stress).
stress
The push, pull, or shear that a material feels when subjected to a force; formally, the force applied per unit area over which the force acts.
Strike
The compass trend of an imaginary horizontal line on a plane.
strike-slip fault
A fault in which one block slides horizontally past another (and therefore parallel to the strike line), so there is no relative vertical motion.
syncline
A trough-shaped fold whose limbs dip toward the hinge.
tension
A stress that pulls on a material and could lead to stretching.
thrust fault
A gently dipping reverse fault; the hanging-wall block moves up the slope of the fault.
Uplift
The upward vertical movement of the ground surface, as occurs during mountain building.
vein
A seam of minerals that forms when dissolved ions carried by water solutions precipitate in cracks.
Cambrian explosion
The remarkable diversification of life, indicated by the fossil record, that occurred at the beginning of the Cambrian Period.
carbon-14 (14C) dating
A radiometric dating process that can tell us the age of organic material containing carbon originally extracted from the atmosphere.
contact
The boundary surface between two rock bodies (as between two stratigraphic formations, between an igneous intrusion and adjacent rock, between two igneous rock bodies, or between rocks juxtaposed by a fault).
correlation
The process of defining the age relations between the strata at one locality and the strata at another.
cross-cutting relations
A means of determining the relative age of rock by looking at which rock or structure cuts another; the feature that has been cut is older.
daughter isotope
The decay product of radioactive decay.
eon
The largest subdivision of geologic time.
Epoch
An interval of geologic time representing the largest subdivision of a period.
era
An interval of geologic time representing the largest subdivision of the Phanerozoic Eon.
fossil succession
The principle that the assemblage of fossil species in a given sequence of sedimentary strata differs from that found in older sequences or in younger sequences; a given species appears at a certain level and then disappears (goes extinct) at a higher level.
geologic column
A composite stratigraphic chart that represents the entirety of the Earth's history.
geologic map
A map showing the distribution of rock units and structures across a region.
geologic time
The span of time since the formation of the Earth.
geologic time scale
A scale that describes the intervals of geologic time.
half-life
The time it takes for half of a group of a radioactive element's isotopes to decay.
isotope
Different versions of a given element that have the same atomic number but different atomic weights.
isotopic dating
The science of dating geologic events in years by measuring the ratio of parent radioactive atoms to daughter product atoms.
numerical age
The age of a rock or structure as specified in years; referred to as Òabsolute ageÓ in older literature.
original horizontality
The principle that sediments are deposited in nearly horizontal layers.
parent isotope
A radioactive isotope that undergoes decay.
period
An interval of geologic time representing a subdivision of a geologic era.
Precambrian
The interval of geologic time between Earth's formation about 4.57 Ga and the beginning of the Phanerozoic Eon 542 Ma.
radioactive decay
The process by which a radioactive atom undergoes fission or releases particles thereby transforming into a new element.
relative age
The age of one geologic feature with respect to another.
stratigraphic column
A cross-section diagram of a sequence of strata summarizing information about the sequence.
stratigraphic formation
A recognizable layer of a specific sedimentary rock type or set of rock types, deposited during a certain time interval, that can be traced over a broad region.
superposition
The principle that younger layers of sediment are deposited on older layers of sediment; thus, in a sequence of strata, the oldest layer is at the base.
unconformity
A boundary between two different rock sequences representing an interval of time during which new strata were not deposited and/or were eroded.
uniformitarianism
The principle that the same physical processes observed today are responsible for the formation of ancient geologic features; put concisely, Òthe present is the key to the past.Ó
Ancestral Rockies
The late Paleozoic uplifts of the Rocky Mountain region; they eroded away long before the present Rocky Mountains formed.
Archean Eon
The middle Precambrian Eon.
Basin and Range Province
A broad, Cenozoic continental rift that has affected a portion of the western United States in Nevada, Utah, and Arizona; in this province, tilted fault blocks form ranges, and alluvium-filled valleys are basins.
Cambrian explosion
The remarkable diversification of life, indicated by the fossil record, that occurred at the beginning of the Cambrian Period.
cratonic platform
A province in the interior of a continent in which Phanerozoic strata bury most of the underlying Precambrian rock.
differentiation
In the context of planet formation, the process by which a planet separates into a metallic core and a rocky mantle very early in its history.
epicontinental sea
A shallow sea overlying a continent.
Hadean Eon
The oldest of the Precambrian eons; the time between Earth's origin and the formation of the first rocks that have been preserved.
Laramide orogeny
The mountain-building event that lasted from about 80 Ma to 40 Ma, in western North America; in the United States, it formed the Rocky Mountains as a result of basement uplift and the warping of the younger overlying strata into large monoclines.
Pangaea
A supercontinent that assembled at the end of the Paleozoic Era.
Phanerozoic Eon
The most recent eon, an interval of time from 542 Ma to the present.
Pleistocene ice age
The period of time from about 2 Ma to 14,000 years ago, during which the Earth experienced an ice age.
Proterozoic Eon
The most recent of the Precambrian eons.
Rodinia
The most recent of the Precambrian eons.
shield
An older, interior region of a continent.
snowball Earth
Our planet during periods in the Precambrian when its entire surface was ice covered.
stratigraphic sequence
An interval of strata deposited during periods of relatively high sea level, and bounded above and below by regional unconformities.
stromatolite
Layered mounds of sediment formed by cyanobacteria; cyanobacteria secrete a mucuous-like substance to which sediment sticks, and as each layer of cyanobacteria gets buried by sediment, it colonizes the surface of the new sediment, building a mound upward.
superplume
A huge mantle plume.
biofuel
Gas or liquid fuel made from plant material (biomass). Examples of biofuel include alcohol (from fermented sugar), biodiesel from vegetable oil, and wood.
cement
Mineral material that precipitates from water and fills the spaces between grains, holding the grains together.
coal
An organic sedimentary rock formed from plant debris.
coalbed methane
Natural gas produced during the diagenesis of coal.
coal gasification
The transformation, by human activity, of coal into various gases.
coal rank
A measurement of the carbon content of coal; higher-rank coal forms at higher temperatures.
energy
The capacity to do work.
energy resource
Something that can be used to produce work; in a geologic context, a material (such as oil, coal, wind, flowing water) that can be used to produce energy.
fossil fuel
An energy resource such as oil or coal that comes from organisms that lived long ago, and thus stores solar energy that reached the Earth then.
gas hydrate
An ice-like solid consisting of water and methane.
geothermal energy
Heat and electricity produced by using the internal heat of the Earth.
greenhouse effect
The trapping of heat in the Earth's atmosphere by carbon dioxide and other greenhouse gases, which absorb infrared radiation; somewhat analogous to the effect of glass in a greenhouse.
hydrocarbon reserve
An accumulation of accessible oil and gas.
hydrocarbon
A chain-like or ring-like molecule made of hydrogen and carbon atoms; petroleum and natural gas are hydrocarbons.
Kerogen
The waxy molecules into which the organic material in shale transforms on reaching about 100 ¡C. At higher temperatures, kerogen transforms into oil.
meltdown (of nuclear reactor)
The melting of the fuel rods in a nuclear reactor that occurs if the rate of fission becomes too fast and the fuel rods become too hot.
Metal
A solid composed almost entirely of atoms of metallic elements; it is generally opaque, shiny, smooth, and malleable, and can conduct electricity.
mineral resources
The minerals extracted from the Earth's upper crust for practical purposes.
nuclear reactor
The part of a nuclear power plant where the fission reactions occur.
nuclear waste
Radioactive materials produced in a nuclear reactor.
Oil Age
The period of human history, including our own, so named because the economy depends on oil.
oil shale
Shale containing kerogen.
oil window
The narrow range of temperatures under which oil can form in a source rock.
ore
Rock containing native metals or a concentrated accumulation of ore minerals.
ore deposit
An economically significant accumulation of ore.
peat
Compacted and partially decayed vegetation accumulating beneath a swamp.
permeability
The degree to which a material allows fluids to pass through it via an interconnected network of pores and cracks.
photosynthesis
The process during which chlorophyll-containing plants remove carbon dioxide from the atmosphere, form tissues, and expel oxygen back to the atmosphere.
porosity
The total volume of empty space (pore space) in a material, usually expressed as a percentage.
reservoir rock
Rock with high porosity and permeability, so it can contain an abundant amount of easily accessible oil.
resource
A supply of useable material.
salt dome
A rising bulbous dome of salt that bends up the adjacent layers of sedimentary rock.
tar sand
Sandstone reservoir rock in which less viscous oil and gas molecules have either escaped or been eaten by microbes, so that only tar remains.
trap
In the context of hydrocarbons, a trap is a geologic configuration that accumulates and holds oil underground.
angle of repose
The angle of the steepest slope that a pile of uncemented material can attain without collapsing from the pull of gravity.
Avalanche
A turbulent cloud of debris mixed with air that rushes down a steep hill slope at high velocity; the debris can be rock and/or snow.
Creep
The gradual downslope movement of regolith.
debris fall
A sudden collapse of disaggregated material on a steep slope.
debris flow
A downslope movement of mud mixed with larger rock fragments.
debris slide
A sudden downslope movement of material consisting only of regolith.
failure surface
The detachment or sliding horizon on which downslope movement of rock or debris occurs.
head scarp
The distinct step along the upslope edge of a slump where the regolith detached.
Lahar
A thick slurry formed when volcanic ash and debris mix with water, either in rivers or from rain or melting snow and ice on the flank of a volcano.
Landslide
A sudden movement of rock and debris down a nonvertical slope.
Liquefaction
The transformation of seemingly solid sediment into a liquid-like slurry, in response to ground shaking.
mass movement
The gravitationally caused downslope transport of rock, regolith, snow, or ice.
mudflow
A downslope movement of mud at slow to moderate speed.
natural hazard
A situation or setting caused by natural processes that can result in damage to society.
Rockfall
A sudden collapse of bedrock down a steep slope.
rock slide
A sudden downslope movement of rock.
slump
Downslope movement in which a mass of regolith detaches from its substrate along a spoon-shaped sliding surface and slips downward semicoherently.
solifluction
The type of creep characteristic of tundra regions; during the summer, the uppermost layer of permafrost melts, and the soggy, weak layer of ground then flows slowly downslope in overlapping sheets.
talus arpon
A wedge-shaped pile of rock fragments that accumulates at the base of a cliff.
undercutting
Excavation at the base of a slope that results in the formation of an overhang.
alluvial fan
A gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semi-arid regions.
alluvium
Sorted sediment deposited by a stream.
annual probability
The likelihood, expressed as a percentage, that an event (e.g., a flood of a given size) will happen in a given year.
antecedent stream
A stream that cuts across an uplifted mountain range; the stream must have existed before the range uplifted and must then have been able to downcut as fast as the land was rising.
bar
(1) A sheet or elongate lens or mound of alluvium; (2) a unit of air pressure measurement approximately equal to 1 atm.
base level
The lowest elevation a stream channel's floor can reach at a given locality.
braided stream
A sediment-choked stream consisting of entwined subchannels.
capacity
The total volume of sediment that a stream can carry.
channel
A trough dug into the ground surface by flowing water.
competence
The ability of flowing water to carry sediment, as represented by the largest clast size that the stream can transport.
delta
A wedge of sediment formed at a river mouth when the running water of the stream enters standing water, the current slows, the stream loses competence, and sediment settles out.
discharge
The volume of water in a conduit or channel passing a point in one second.
distributaries
The fan of small streams formed where a river spreads out over its delta.
downcutting
The process in which water flowing through a channel cuts into the substrate and deepens the channel relative to its surroundings.
drainage basin
An array of interconnecting streams that together drain an area.
drainage divide
A highland or ridge that separates one watershed from another
drainage network
An array of interconnecting streams that together drain an area.
ephemeral stream
A stream whose bed lies above the water table, so that the stream flows only when the rate at which water enters the stream from rainfall or meltwater exceeds the rate at which water infiltrates the ground below.
flash flood
A flood that occurs during unusually intense rainfall or as the result of a dam collapse, during which the floodwaters rise very fast.
flood
An event during which the volume of water in a stream becomes so great that it covers areas outside the stream's normal channel.
floodplain
The flat land on either side of a stream that becomes covered with water during a flood.
headward erosion
The process by which a stream channel lengthens up its slope as the flow of water increases.
longitudinal profile
A cross-sectional image showing the variation in elevation along the length of a river.
Meander
A snake-like curve along a stream's course.
natural levees
A pair of low ridges that appear on either side of a stream and develop as a result of the accumulation of sediment deposited naturally during flooding.
permanent stream
A stream that flows year-round because its bed lies below the water table, or because more water is supplied from upstream than can infiltrate the ground.
point bar
A wedge-shaped deposit of sediment on the inside bank of a meander.
Rapids
A reach of a stream in which water becomes particularly turbulent; as a consequence, waves develop on the surface of the stream.
recurrence interval
The average time between successive geologic events.
seasonal flood
Floods that appear almost every year during seasons when rainfall is heavy or when winter snows start to melt.
sheetwash
A film of water less than a few millimeters thick that covers the ground surface during heavy rains.
stream
A ribbon of water that flows in a channel.
stream piracy
The situation in which headward erosion causes one stream to intersect the course of another, previously independent stream, so that the intersected stream starts to flow down the channel of the first stream.
stream rejuvenation
The renewed downcutting of a stream into a floodplain or peneplain, caused by a relative drop of the base level.
stream terrace
A flat surface, underlain by alluvium, that borders a stream; terraces form when the stream cuts down into the alluvium that it had deposited previously.
superposed stream
A stream whose geometry has been laid down on a rock structure and is not controlled by the structure.
tributary
A smaller stream that flows into a larger stream.
V-shaped valley
A valley whose cross-sectional shape resembles a V; the valley probably has a river running down the point of the V.
waterfall
A place where water drops over an escarpment.
abyssal plain
A broad, relatively flat region of the ocean that lies at least 4.5 km below sea level.
active continental margin
A continental margin that coincides with a plate boundary.
barrier island
An offshore sand bar that rises above the mean high-water level, forming an island.
bathymetry
Variation in depth.
beach
A band of sand or gravel that lies along a coastline; wave action affects the profile and sediment size of a beach.
coast
The boundary region between land and the sea.
coastal plain
Low-relief regions of land adjacent to the coast.
coastal wetland
Low-relief regions of land adjacent to the coast.
continental shelf
A broad, shallowly submerged region of a continent along a passive margin.
coral reef
A mound of coral and coral debris forming a region of shallow water.
current
(1) A well-defined stream of ocean water; (2) the moving flow of water in a stream.
emergent coasts
A coast where the land is rising relative to sea level or sea level is falling relative to the land.
estuary
An inlet in which seawater and river water mix, created when a coastal valley is flooded because of either rising sea level or land subsidence.
eye (of hurricane)
The relative calm in the center of a hurricane.
Fjord
A deep, glacially carved, U-shaped valley flooded by rising sea level.
hurricane
A huge rotating storm, resembling a giant spiral in map view, in which sustained winds blow over 119 km per hour.
lagoon
A body of shallow seawater separated from the open ocean by a barrier island.
longshore current
A current that flows parallel to a beach.
offshore bar
An elongate deposit of sand separated from the land by water.
passive continental margin
A continental margin that is not a plate boundary.
sand spit
An area where the beach stretches out into open water across the mouth of a bay or estuary.
seamount
An isolated submarine mountain.
storm surge
Excess seawater driven landward by wind during a storm; the low atmospheric pressure beneath the storm allows sea level to rise locally, increasing the surge.
submarine canyon
A narrow, steep canyon that dissects a continental shelf and slope.
submergent coast
A coast at which the land is sinking relative to sea level.
thermohaline circulation
The rising and sinking of water driven by contrasts in water density, which is due in turn to differences in temperature and salinity; this circulation involves both surface and deep-water currents in the ocean.
tidal flat
A broad, nearly horizontal plain of mud and silt, exposed or nearly exposed at low tide but totally submerged at high tide.
Tide
The daily rising or falling of sea level at a given point on the Earth.
Tide-generating force
The force, caused in part by the gravitational attraction of the Sun and Moon, and in part by the centrifugal force created by the Earth's spin, that generates tides.
wave base
The depth, approximately equal in distance to half a wavelength in a body of water, beneath which there is no wave movement.
wave-cut bench
A platform of rock, cut by wave erosion, at the low-tide line that was left behind a retreating cliff.
wave-cut notch
A notch in a coastal cliff cut out by wave erosion.
wave refraction
The bending of waves as they approach a shore so that their crests make no more than a 5¡ angle with the shoreline.
Aquifer
Sediment or rock that transmits water easily.
aquitard
Sediment or rock that does not transmit water easily and therefore retards the motion of the water.
artesian spring
A place where groundwater gushes out of the ground under pressure.
artesian well
A well in which water rises on its own.
cone of depression
The downward-pointing, cone-shaped surface of the water table in a location where the water table is experiencing drawdown because of pumping at a well.
Darcy's law
A mathematical equation stating that a volume of water, passing through a specified area of material at a given time, depends on the material's permeability and hydraulic gradient.
discharge area
A location where groundwater flows back up to the surface, and may emerge at springs.
geothermal region
A region of current or recent volcanism in which magma or very hot rock heats up groundwater, which may discharge at the surface in the form of hot springs and/or geysers.
geyser
A fountain of steam and hot water that erupts periodically from a vent in the ground in a geothermal region.
Groundwater
Water that resides under the surface of the Earth, mostly in pores or cracks of rock or sediment.
groundwater contamination
The introduction of harmful and/or nonnatural chemicals to groundwater.
hot spring
A spring that emits water ranging in temperature from about 30 ¡C to 104 ¡C.
hydraulic gradient
The slope of the water table.
hydraulic head
The elevation to which groundwater rises in a pipe drilled into the ground; in non-artesian systems, the head is the water table.
karst landscape
A region underlain by caves in limestone bedrock; the collapse of the caves creates a landscape of sinkholes separated by higher topography, or of limestone spires separated by low areas.
oasis
A verdant region surrounded by desert, occurring at a place where natural springs provide water at the surface.
ordinary well
A well whose base penetrates below the water table, and can thus provide water.
perched water table
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.
permeability
The degree to which a material allows fluids to pass through it via an interconnected network of pores and cracks.
pore
A small open space within sediment or rock.
Porosity
The total volume of empty space (pore space) in a material, usually expressed as a percentage.
recharge area
A location where water enters the ground and infiltrates down to the water table.
Sinkhole
A circular depression in the land that forms when an underground cavern collapses.
soil moisture
Underground water that wets the surface of the mineral grains and organic material making up soil, but lies above the water table.
speleothem
A formation that grows in a limestone cave by the accumulation of travertine precipitated from water solutions dripping in a cave or flowing down the wall of a cave.
spring
A natural outlet from which groundwater flows up onto the ground surface.
water table
The boundary, approximately parallel to the Earth's surface, that separates substrate in which groundwater fills the pores from substrate in which air fills the pores.
well
A hole in the ground dug or drilled in order to obtain water.
alluvial fan
A gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semi-arid regions.
Butte
A medium-sized, flat-topped hill in an arid region.
chimney
(1) A conduit in a magma chamber in the shape of a long vertical pipe through which magma rises and erupts at the surface; (2) an isolated column of strata in an arid region.
cliff retreat
The change in the position of a cliff face caused by erosion.
deflation
The process of lowering the land surface by wind abrasion.
desert
A region so arid that it contains no permanent streams except for those that bring water in from elsewhere, and has very sparse vegetation cover.
desertification
The process of transforming nondesert areas into desert.
desert pavement
A mosaic-like stone surface forming the ground in a desert.
desert varnish
A dark, rusty-brown coating of iron oxide and magnesium oxide that accumulates on the surface of rock in an arid environment.
dry wash
The channel of an ephemeral stream when empty of water.
inselberg
An isolated mountain or hill in a desert landscape created by progressive cliff retreat, so that the hill is surrounded by a pediment or an alluvial fan.
lag deposit
A surface accumulation of coarser sediment that forms where wind has blown away finer sediment.
mesa
A large, flat-topped hill (with a surface area of several square kilometers) in an arid region.
pediment
The broad, nearly horizontal bedrock surface at the base of a retreating desert cliff.
playa
The flat, typically salty lake bed that remains when all the water evaporates in drier times; forms in desert regions.
rain shadow
The inland side of a mountain range, which is arid because the mountains block rain clouds from reaching the area.
saltation
The movement of a sediment in which grains bounce along their substrate, knocking other grains into the water column (or air) in the process.
surface load
Sediment that rolls or bounces in wind along the ground surface.
suspended load
Tiny solid grains carried along by a stream without settling to the floor of the channel.
talus apron
A wedge-shaped pile of rock fragments that accumulates at the base of a cliff.
ventifact
A desert rock whose surface has been faceted by the wind.
arte
A residual knife-edge ridge of rock that separates two adjacent cirques.
basal sliding
The phenomenon in which meltwater accumulates at the base of a glacier, so that the mass of the glacier slides on a layer of water or on a slurry of water and sediment.
Cirque
A bowl-shaped depression carved by a glacier on the side of a mountain.
continental glacier
A vast sheet of ice that spreads over thousands of square kilometers of continental crust.
crevasse
A large crack that develops by brittle deformation in the top 60 m of a glacier.
drumlin
A streamlined, elongate hill formed when a glacier overrides glacial till.
end moraine
A low, sinuous ridge of till that develops when the terminus (toe) of a glacier stalls in one position for a while.
equilibrium line
The boundary between the zone of accumulation and the zone of ablation on a glacier.
erratic
A boulder or cobble that was picked up by a glacier and deposited hundreds of kilometers away from the outcrop from which it detached.
esker
A ridge of sorted sand and gravel that snakes across a ground moraine; the sediment of an esker was deposited in subglacial meltwater tunnels.
fjord
A deep, glacially carved, U-shaped valley flooded by rising sea level.
glacial advance
The forward movement of a glacier's toe when the supply of snow exceeds the rate of ablation.
glacial retreat
The movement of a glacier's toe back toward the glacier's origin; glacial retreat occurs if the rate of ablation exceeds the rate of supply.
glacial striations
Scratches or troughs carved into rock by the sediment embedded in ice at the base of a flowing glacier.
glacial till
Sediment transported by flowing ice and deposited beneath a glacier or at its toe.
glacier
A river or sheet of ice that slowly flows across the land surface and lasts all year long.
hanging valley
A glacially carved tributary valley whose floor lies at a higher elevation than the floor of the trunk valley.
horn
A pointed mountain peak surrounded by at least three cirques.
ice age
An interval of time in which the climate was colder than it is today, glaciers occasionally advanced to cover large areas of the continents, and mountain glaciers grew; an ice age can include many glacials and interglacials.
iceberg
A large block of ice that calves off the front of a glacier and drops into the sea.
kettle hole
A circular depression in the ground made when a block of ice calves off the toe of a glacier, becomes buried by till, and later melts.
lateral moraine
A strip of debris along the side margins of a glacier.
loess
Layers of fine-grained sediments deposited from the wind; large deposits of loess formed from fine-grained glacial sediment blown off outwash plains.
medial moraine
A strip of sediment in the interior of a glacier, parallel to the flow direction of the glacier, formed by the lateral moraines of two merging glaciers.
Milankovitch cycles
Climate cycles that occur over tens to hundreds of thousands of years, because of changes in Earth's orbit and tilt.
moraine
A sediment pile composed of till deposited by a glacier.
mountain glacier
A glacier that exists in or adjacent to a mountainous region.
patterned ground
A polar landscape in which the ground splits into pentagonal or hexagonal shapes.
permafrost
Permanently frozen ground.
plastic deformation
The deformational process in which mineral grains behave like plastic and, when compressed or sheared, become flattened or elongate without cracking or breaking.
pluvial lake
A lake formed to the south of a continental glacier as a result of enhanced rainfall during an ice age.
polar glacier
Dry-bottom glacier.
roche moutonnŽe
A glacially eroded hill that becomes elongate in the direction of flow and asymmetric; glacial rasping smoothes the upstream part of the hill into a gentle slope, while glacial plucking erodes the downstream edge into a steep slope.
sea ice
Ice formed by the freezing of the surface of the sea.
snowball Earth
Our planet during periods in the Precambrian when its entire surface was ice covered.
temperate glacier
A glacier that exists in regions where it is warm enough for liquid water to occur in films between the grains of ice.
terminal moraine
The end moraine at the farthest limit of glaciation.
tidewater glacier
...
toe (terminus)
...
U-shaped valley
...
zone of ablation
...
zone of accumulation
...
acid rain
Precipitation in which air pollutants react with water to make a weak acid that then falls from the sky.
biogeochemical cycle
The exchange of chemicals between living and nonliving reservoirs in the Earth System.
climate
The average weather conditions, along with the range of conditions, of a region over a year.
ecosystem
An environment and its inhabitants.
global change
The transformations or modifications of both physical and biological components of the Earth System through time.
global cooling
A fall in the average atmospheric temperature.
global warming
A rise in the average atmospheric temperature.
greenhouse gases
Atmospheric gases, such as carbon dioxide and methane, that regulate the Earth's atmospheric temperature by absorbing infrared radiation.
greenhouse period
Relatively warm global climate leading to the rising of sea level for an interval of geologic time.
icehouse period
A period of time when the Earth's temperature was cooler than it is today and ice ages could occur.
mass-extinction event
A time when vast numbers of species abruptly vanish.
ozone hole
An area of the atmosphere, over polar regions, from which ozone has been depleted.
paleoclimate
The past climate of the Earth.
pollution
Contaminants that have been introduced into the Earth System by human activity.
supercontinent cycle
The process of change during which supercontinents develop and later break apart, forming pieces that may merge once again in geologic time to make yet another supercontinent.
sustainable growth
Enlargement of society and the economy in ways that be supported indefinitely by renewable natural resources.