Geology Final Exam Review

Till

All sediment deposited directly by glacial ice.

Taconic Orogeny

An Ordovician episode of mountain building that resulted in the deformation of the Appalachian mobile belt.

Fluid Activity

An agent of metamorphism in which water and carbon dioxide promote metamorphism by increasing the rate of chemical reactions.

Heat

An agent of metamorphism.

P-Wave Shadow Zone

An area between 103 and 143 degrees from an earthquake focus where little P-wave energy is recorded by seismographs.

Fiord

An arm of the sea extending into a glacial trough eroded below sea level.

Guide Fossil

An easily identified fossil with an extensive geographic distribution and short geologic range useful for determining the relative ages of rocks in different ages.

Ion

An electrically charged atom produced by adding or removing electrons from the outermost electron shell.

Neutron

An electrically neutral particle found in the nucleus of an atom.

Drumlin

An elongate hill of till formed by the movement of a continental glacier or by floods.

Mobile Belt

An elongated area of deformation indicated by folds and faults; generally adjacent to a craton.

Terminal Moraine

An end moraine consisting of a ridge or mound of rubble marking the farthest extent of a glacier.

Recessional Moraine

An end moraine that forms when a glacier's terminus retreats, the stabilizes, and a ridge or mound of till is deposited.

Acadian Orogeny

An episode of Devonian deformation in the northern Appalachian mobile belt resulting from the collision of Baltica with Laurentia.

Pediment

An erosion surface of low relief gently sloping away from the base of a mountain range.

Stream Terrace

An erosional remnant of a floodplain that formed when a stream was flowing at a higher level.

Volcanic Neck

An erosional remnant of the material that solidified in a volcanic pipe.

Theory

An explanation for some natural phenomenon that has large body of supporting evidence. (To be scientific a theory must be testable.)

Milankovitch Theory

An explanation for the cyclic variations in climate and the onset of ice ages as a result of irregularities in Earth's rotation and orbit.

Elastic Rebound

An explanation for the sudden release of energy that causes earthquakes when deformed rocks fracture and rebound to their original undeformed condition.

Volcanic (Extrusive Igneous) Rock

An igneous rock formed when magma is extruded onto Earth's surface where it cools and crystallizes, or when pyroclastic materials become consolidated.

Porphyritic Texture

An igneous texture with minerals of markedly different sizes.

Bed

An individual layer of rock, especially sediment or sedimentary rock.

Plate

An individual segment of the lithosphere that moves over the asthenosphere.

Seismograph

An instrument that detects, records, and measures the various waves produced by the earthquake.

Little Ice Age

An interval from about 1500 to the mid- to late-1800s during which glaciers expanded to their greatest historic event.

Pluton

An intrusive igneous body that forms when magma intruded into or formed in place within the crust.

Butte

An isolated, steep-sided, pinnacle-like hill formed when resistant cap rock is breached, allowing erosion of less resistance underlying rocks.

Richter Magnitude Scale

An open-ended scale that measures the amount of energy released during an earthquake.

Crater

An oval to circular depression at the summit of a volcano resulting from the eruption of lava, pyroclastic materials, and gases.

Angular Unconformtiy

An unconformity below which older rocks dip at a different angle (usually steeper) than overlying strata.

Nonconformity

An unconformity in which stratified sedimentary rock rocks overlie an erosion surface cut into igneous or metamorphic rocks.

Disconformity

An unconformity in which the rock layers above and below are parallel.

Wave

An undulation on the surface of a body water, resulting in the water surface rising and falling.

Desert

Any area that receives less than 25 cm of rain per year and that has a high evaporation rate.

Sedimentary Facies

Any aspect of a sedimentary rock unit that makes it recognizably different from adjacent sedimentary rocks of the same or approximately the same age.

Beach

Any deposit of sediment extending landward from low tide to a change in topography of where permanent vegetation.

Geologic Structure

Any feature in rocks that results from deformation, such as folds, joints, and faults.

Sedimentary Structure

Any feature in sedimentary rock that formed at or shortly after the time of deposition, such as cross-bedding animal burrows, and mud cracks.

Rock-forming Material

Any material common in rocks that is important in their identification and classification.

Country Rock

Any preexisting rock that has been intruded by a pluton or altered by metamorphism.

Soil Degradation

Any process leading up to a loss of soil productivity; may involve erosion, chemical pollution, or compaction.

Sedimentary Rock

Any rock composed of sediment, such as limestone and sandstone.

Igneous Rock

Any rock formed by cooling and crystallization of magma or lava by the consolidation of pyroclastic materials.

Metamorphic Rock

Any rock that has been changed from its original condition by heat, pressure, and the chemical activity of fluids, as in marble and slate.

Metamorphic Rock

Any rock that has been changed from its original condition by heat, pressures, and the chemical activity of fluids, as in marble and slate.

Carbonate Rock

Any rock, such as limestone and dolostone, made up mostly of carbonate minerals.

Biochemical Sedimentary Rock

Any sedimentary rock produced by the chemical activities of organisms.

Evaporite

Any sedimentary rock, such as rock salt, formed by inorganic chemical precipitation of minerals from evaporating water.

Ferromagnesian Silicate

Any silicate mineral that contains iron, magnesium, or both.

Depositional Environment

Any site such as a floodplain or beach where physical, biologic, and chemical processes yield a distinctive kind of sedimentary deposit.

Compound

Any substance resulting from the bonding of two or more different elements.

Clevage

Breakage along internal planes of weakness in mineral cycle.

Pelagic Clay

Brown or red deep-sea sediment composed of clay-sized particles.

Pillow Lava

Bulbous masses of basalt, resembling pillows, formed when lava is rapidly chilled under water.

Geothermal Energy

Energy that comes from stream and hot water trapped within Earth's crust.

Laramide Orogeny

A Late Cretaceous to Early Cenozoic episode of deformation in the area of the present-day Rocky Mountains.

Laurentia

A Proterozoic continent composed mostly of North America, Greenland, and parts of Scotland and Scandinavia.

Monocline

A bend or flexture in otherwise horizontal or uniformly dipping rock layers.

Wave-Cut Platform

A beveled surface that slopes gently sea forward; formed by the erosion and retreat of a sea cliff.

Discontinuity

A boundary across which seismic wave velocity of direction of travel changes abruptly, such as the mantle-core boundary.

Fracture

A break in rock resulting from intense applied pressure.

Unconformity

A break in the geologic record represented by an erosional surface separating younger strata from older rocks.

Mesa

A broad, flat-topped erosional remnant bounded on all sides by steep slopes.

Lava Dome

A bulbous, steep-sided mountain formed by viscous magma moving upward through a volcanic conduit.

Geologic Time Scale

A chart arranged so that the designation for the earliest part of geologic time appears at the bottom, followed upward by progressively younger time designations.

Covalent Bond

A chemical bond formed by the sharing of electrons between atoms.

Ionic Bond

A chemical bond resulting from the attraction between positively and negatively charged ions.

Basin

A circular fold in which all strata dip inward toward a central point and the youngest exposed strata are in the center.

Submergent Coast

A coast along which sea level rises with respect to the land or the land subsidies.

Emergent Coast

A coast where the land has risen with respect to sea level.

Alluvium

A collective term for all detrital sediment transported and deposited by running water.

Glacial Drift

A collective term for all sediment deposited directly by glacial ice and by meltwater streams.

System

A combination of related parts the interact in an organized fashion; Earth system include the atmosphere, hydrosphere, biosphere and solid Earth.

Silica

A compound of silicon and oxygen.

P-Wave

A compressional, or push-pull, wave; the fastest seismic wave and one that can travel through solids, liquids, and gases; also called a primary wave.

Resource

A concentration of naturally occurring solid, liquid, or gas material in, or on, Earth's crust in such form and amount that economic extraction of a commodity from the concentration is currently or potentially feasible.

Alluvial Fan

A cone-shaped accumulation of mostly sand and gravel deposited where a stream flows from a mountain valley onto an adjacent lowland.

Cone of Depression

A cone-shaped depression around a well where water is pumped from an aquifer faster than it can be replaced.

Artesian System

A confined groundwater system with high hydrostatic pressure that causes water to rise above the level of the aquifer.

Oceanic- Continental Plate Boundary

A convergent plate boundary along which oceanic lithosphere is subducted beneath continental lithosphere.

Continental-Continental Plate Boundary

A convergent plate boundary along which two continental lithospheric plates collide.

Oceanic-Oceanic Plate Boundary

A convergent plate boundary along which two oceanic plates collide and one is subducted beneath the other.

Anticline

A convex upward fold in which the oldest exposed rocks coincide with the fold axis and all strata dip away from the axis.

Mud Crack

A crack in clay-rich sediment that forms in response to drying and shrinkage.

Submarine Hydrothermal Vent

A crack, of fissure, in the seafloor through which superheated water issues.

Parabolic Dune

A crescent-shaped dine with tips pointing upwind.

Barchan Dune

A crescent-shaped sand dune with its tips pointing downward.

Longshore Current

A current resulting from wave refraction found between the breaker zone and a beach that flows parallel to the shoreline.

Oxbow Lake

A cutoff meander filled with water.

Mantle Plume

A cylindrical mass of magma rising from the mantle toward the surface. (Hawaiian Islands)

Incised Meander

A deep, meandering canyon cut into bedrock by a stream or river.

Delta

A deposit of sediment where a stream or river enters a lake or the ocean.

Sinkhole

A depression in the ground that forms by the solution of the underlying carbonate rocks or by the collapse of a cave roof.

Normal Fault

A dip-slip fault on which the hanging wall block has moved downward relative to the footwall block.

Soil Horizon

A distinct soil layer that differs from other soil layers in texture, structure, composition, and color.

Ice Cap

A dome-shaped mass of glacial ice that cover less than 50000 km.

Shield Volcano

A dome-shaped volcano with a low, rounded profile built up mostly by overlapping basalt lava flows.

Syncline

A down-arched fold in which the youngest exposed rocks coincide with the fold axis and all strata dip toward the axis.

Playa

A dry lake bed found in deserts.

Strike-Slip Fault

A fault involving horizontal movement of blocks of rock on opposites side of a fault plane.

Dip-Slip Fault

A fault on which all movement is parallel with the dip of the fault plane.

Oblique-Slip Fault

A fault showing both dip-slip and strike-slip movement.

Fault Plane

A fault surface that is more or less planar.

Spit

A fingerlike projection of a beach into a body of water such as a bay.

Viscosity

A fluid's resistance to flow.

Joint

A fracture along which no movement has occurred or where movement is perpendicular to the fracture surface.

Fault

A fracture along which rocks on opposite sides of the fracture have moved parallel with the fracture surface.

Pyroclastic (Fragmental) Texture

A fragmental substances, such as ash, that are exposively ejected from a volcano

Deformation

A general term for any change in shape or volume, or both, of rocks in response to stress; involves folding and fracturing.

Valley Glacier

A glacier confined to a mountain valley or an interconnected sytem of mountain valleys.

Continental Glaciers

A glacier that covers a vast area and is not confined by topography; also called an ice sheet.

Metamorphic Facies

A group of metamorphic rocks characterized by particular minerals that formed under the same board temperature and pressure conditions.

Rock Cycle

A group of processes through which Earth materials may pass as they are transformed from one major rock to another.

Volcano

A hill or mountain formed around a vent as a result of the eruption of lava and pyroclastic materials.

Geyser

A hot spring that periodically ejects hot water and stream.

Tsunami

A large sea wave that is usually produced by an earthquake, but can also result from submarine landslides and volcanic eruptions.

Exfoliation Dome

A large, rounded dome of rock resulting when concentric layers of rock are stripped from the surface of a rock mass.

Valley

A linear depression bounded by higher areas such as ridges or mountains.

Greenstone Belt

A linear or podlike association of igneous and sedimentary rocks; typically synclinal and consists of lower and middle volcanic units and an upper sedimentary rock unit.

Orogen

A linear part of Earth's crust that was, or is, being deformed during an orogeny.

Hot Spot

A localized zone of melting below the lithosphere that probably overlies a mantle plume; detected by volcanism at the surface.

Scientific Method

A logical, orderly approach that involved gathering data, formulating and testing hypotheses, and proposing theories.

Longitudinal Dune

A long ridge of sand generally parallel to the direction of the prevailing wind.

Valley Train

A long, narrow deposit of stratified drift confined within a glacial valley.

Oceanic Trench

A long, narrow feature restricted to active continental margins and along which subduction occurs.

Barrier Island

A long, narrow island of sand parallel to a shoreline but separated from the mainland by a lagoon.

Esker

A long, sinuous ridge stratified drift deposited by running water in a tunnel beneath stagnant ice.

Floodplain

A low-lying, flat area adjacent to a channel that is partly or completely water-covered when a stream or river overflows its banks.

Glacier

A mass of ice on land that moves by plastic flow and basal slip.

Permeability

A material's capacity to transmit fluids.

Velocity

A measure of distance traveled per unit of time, as in the flow of velocity in a stream or river.

Salinity

A measure of the dissolved solids in seawater, usually expressed in parts per thousand.

Dip

A measure of the maximum angular deviation of an inclined plane from horizontal.

Pressure Release

A mechanical weathering process in which rocks that formed under pressure expand on being exposed at the surface.

Salt Crystal Growth

A mechanical weathering process in which salt crystals growing in cracks and pores disaggregate rocks.

Nonfoliated Texture

A metamorphic texture in which there is no discernable preferred orientation of minerals.

Silicate

A mineral that contains silica, such as quartz.

Index Mineral

A mineral that forms with a specific temperature and pressure ranges during metamorphism.

Big Bang

A model for the evolution of the universe in which a dense, hot state was followed by expansion, cooling, and a less-dense state.

Medial Moraine

A moraine carried on the central surface of a glacier; formed where two lateral moraines merge.

Oceanic Ridge

A mostly submarine mountain system composed of basalt found in all ocean basins.

Dune

A mound or ridge of wind-deposited sand.

Reef

A mound-like, wave-resistant structure composed of the skeletons of organisms.

Rip Current

A narrow surface current that flows to sea through the breaker zone.

Arete

A narrow, serrate ridge between two glacial valleys or adjacent cirques.

Cave

A natural subsurface opening generally connected to the surface and large enough for a person to enter.

Crystal

A naturally occurring solid of an element or compound with a specific internal structure that is manifested externally by planar faces, sharp corners, and straight edges.

Mineral

A naturally occurring, inorganic, crystalline solid that has characteristic physical properties and a narrowly defined chemical composition.

Electron

A negatively charged particle of very little mass that encircles the nucleus of an atom.

Ouachita Orogeny

A period of mountain building that took place in the Ouachita mobile belt during the Pennsylvanian Period.

Magnetism

A physical phenomenon resulting from moving electricity and the spin of electrons in some solids in which magnetic substances are attracted toward one another.

End Moraine

A pile or ridge of rubble deposited at the terminus of a glaciers.

Spring

A place where groundwater flows or seeps out of the ground.

Principle of Superpostion

A position holding that in a vertical sequence of underformed sedimentary rocks, the relative ages of the rocks can be determined by their position in the sequence- oldest at the bottom, followed by successively younger layers.

Proton

A positively charged particle found in the nucleus of the atom.

Principle of Cross-Cutting Relationships

A principle holding that an igneous intrusion or fault must be younger than the rocks it intrudes or cuts across.

Principle of Fossil Succession

A principle holding that fossils, and especially groups or assemblages of fossils, succeed one another through time in a regular and predictable order.

Principle of Inclusion

A principle holding that inclusions of fragments in a rock unit are older than the rock unit itself.

Principle of Lateral Continuity

A principle holding that rock layers extend outward in all directions until they terminate.

Principle of Uniformitarianism

A principle holding that we can interpret past events by understanding present-day processes, based of the idea that natural processes have always operated in the same way.

Stoping

A process in which rising magma detaches and engulfs pieces of the country rock.

Assimlation

A process whereby magma changes composition as it reacts with country rock.

Hypothesis

A provisional explanation for observations that is subject to continual testing. (If well-supported by evidence, a hypothesis may be called a theory.)

Dome

A rather circular geologic structure in which all rock layers dip away from a central point and the oldest exposed rocks are in the domes center.

Solution

A reaction in which the ions of a substance become dissociated in a liquid and the solid substance dissolves.

Laterite

A red soil, rich in iron or aluminum, or both, resulting from intense chemical weathering.

Magma Chamber

A reservoir of magma within Earth's upper mantle or lower crust.

Transverse Dune

A ridge of sand with its long axis perpendicular to the wind direction.

Natural Levee

A ridge of sandy alluvium deposited along the margins of a channel during floods.

Glacier Erratic

A rock fragment carried some distance from its source by a glacier and usually deposited on bedrock of a different composition.

Modified Mercalli Intensity Scale

A scale with values from I to XII used to characterize earthquakes based on damage.

Volcanic Explosivity Index (VEI)

A semi-quantitative scale for determining the size of a volcanic eruption based on evaluation of criteria, such as volume of material explosively erupted and height of eruption cloud.

Bowen's Reaction Series

A series of minerals that form in a specific sequence in cooling magma or lava; originally proposed to explain the origin of intermediate and felsic magma from mafic magma.

S-Wave

A shear wave that moves material perpendicular to the direction of travel, thereby producing shear stresses in the material it moves through; also known as a secondary wave; S-waves only travel through solids.

Nonferromagnesian Silicate

A silicate mineral that has no iron or magnesium.

Reverse Fault

A slip-dip fault on which the hanging wall block has moved upward relative to the foot wall block.

Vesicle

A small hole or cavity formed by gas trapped in cooling lava.

Cinder Cone

A small, steep-sided volcano made up of pyroclastic materials resembling cinders that accumulate around a vent.

Glacial Polish

A smooth, glistening rock surface formed by the movement of sediment-laden ice over bedrock.

Rock

A solid aggregate of one or more minerals, as in limestone and granite, or a consolidated aggregate rock fragments, as in conglomerate, or masses of rock-like materials, such as coal and obsidian.

Cyrstalline Solid

A solid in which the constituent atoms are arranged in a regular, three-dimensional framework.

Baymouth Bar

A spit that has grown until it closes off a bay from the open sea or lake.

Hot Spring

A spring in which the water temperature is warmer than the temperature of a human body.

Cirque

A steep-walled, bowl-shaped depression on a mountainside at the upper end of a glacial valley.

Horn

A steep-walled, pyramid-shaped peak formed by the headward erosion of at least three cirques.

Ventifact

A stone with a surface polished, pitted, grooved, or faceted by wind abrasion.

Glacial Striation

A straight scratch rarely more than a few millimeters deep on a rock caused by the movement of sediment-laden glacial ice.

Lava Flow

A stream of magma flowing over Earth's surface.

Meandering Stream

A stream that has a single, sinuous channel with broadly looping curves.

Graded Stream

A stream that has an equilibrium profile in which a delicate balance exists among gradient, discharge, flow velocity, channel characteristics, and sediment load so that neither significant deposition nor erosion takes place within its channel.

Superposed Stream

A stream that once flowed on a higher surface and eroded downward into resistant rocks while maintaining its course.

Braided Stream

A stream with multiple dividing and rejoining channels.

Element

A substance composed of atoms that all have the same properties.

Desert Pavement

A surface mosaic of close-fitting pebble,cobbles, and boulders found in many dry regions; it results from wind erosion of sand and smaller particles.

Rayleigh Wave (R-Wave)

A surface wave in which individual particles of material move in an elliptical path within a vertical plane oriented in the direction of wave movement.

Love Wave (L-Wave)

A surface wave in which the individual particles of material move only back and forth in a horizontal plane perpendicular to the direction of wave travel.

Gyre

A system of ocean currents rotating clockwise in the North and counter clockwise in South.

Dike

A tabular, or sheetlike, discordant pluton.

Hydrothermal

A term referring to hot water, as in hot water or geyser.

Hardness

A term used to express the resistance of mineral to abrasion.

Aphanitic Texture

A texture in igneous rocks in which individual mineral grains are too small to be seen without magnification; results from rapid cooling of magma and generally indicates an extrusive origin.

Foliated Texture

A texture in metamorphic rocks in which platy and elongate minerals are aligned in a parallel fashion.

Solar Nebula Theory

A theory for the evolution of the solar system from a rotating cloud of glass.

Glacial Surge

A time of greatly accelerated flow in a glacier.

Divide

A topographically high area that separates adjacent drainage basins.

Hanging Valley

A tributary glacial valley whose floor is at a higher level than that of the main glacial valley.

Lava Tube

A tunnel beneath the solidified surface of a lava flow through which lava moves; also, the hollow space left when the lava within a tube drains away.

Cross-Bedding

A type of beeing in which layers are deposited at an angle to the surface on which they accumulate, as in sand dunes.

Spherodial Weathering

A type of chemical weathering in which corners and sharp edges of rocks weather more rapidly than flat surfaces, thus, yielding spherical shapes.

Thermal Convection Cell

A type of circulation of material involving only the asthenosphere or the entire mantle during which hot material rises, moves laterally, cools, and sinks, then is reheated and continues the cycle.

Elastic Strain

A type of deformation in which the material returns to its original shape when stress is relaxed.

Fold

A type of geologic structure in which planar features in rock layers such as bedding and foliation have been bent.

Pahoehoe

A type of lava flow with a smooth, ropy surface.

Thermal Expansion and Contraction

A type of mechanical weathering in which the volume of rocks change in response to heating and cooling.

Thrust Fault

A type of reverse fault in which a fault plane dips less than 45 degrees.

Tombolo

A type of spit that extends out from the shoreline and connects to the mainland with the island.

Tension

A type of stress in which forces act in opposite directions but along the same line, thus tending to stretch an object.

U-Shaped Glacial Trough

A valley with steep or vertical walls and a broad, rather flat floor formed by the movement of a glacier through a stream valley.

Shield

A vast area of exposed ancient rocks on a continent; the exposed part of a craton.

Cyclothem

A vertical sequence of cyclically repeating sedimentary rocks resulting from alternating period of marine and nonmairne deposition; commonly containing a coal bed.

Fissure Eruption

A volcanic eruption in which lava or pyroclastic materials issue from a long, narrow fissure (crack) or group of fissures.

Breaker

A wave that steepens as it enters shallow water until it crust plunges forward.

Marine Terrace

A wave-cut platform now above sea level.

Water Well

A well made by digging or drilling into the zone of saturation.

Absaroka Sequence

A widespread association of sedimentary rocks bounded above and below by unconformities; deposited during a Late Mississippian to Early Jurassic transgressive-regressive cycle of the Absaroka Sea.

Sauk Sequence

A widespread association of sedimentary rocks bounded above and below by unconformities; deposited during a Late Neoproterozoic to Early Ordovician transgressive-regressive cycle of the Sauk Sea.

Tippecanoe Sequence

A widespread body of sedimentary rocks bounded above and below by unconformities; deposited during a Middle Ordovician to Early Devonian Transgressive-regressive cycle of the Tippecanoe sea.

Kaskaskia Sequence

A widespread sequence of Middle Devonian to Upper Mississippian sedimentary rocks bounded above and below by unconformities; deposited during a transgressive-regressive cycle of the Kaskaskia Sea.

Circum-Pacific Belt

A zone of seismic and volcanic activity and mountain building that nearly encircles the Pacific Ocean basin.

Mediterranean Belt

A zone of seismic and volcanic activity extending through the Mediterranean region of southern Europe and eastward to Indonesia.

Aureole

A zone surrounding a pluton in which contact metamorphism took place.

Carbon-14 Dating Technique

Absolute dating technique relying on the ratio of C14 to C12 in an organic substance; useful back to about 700000 years ago.

Principle of Horizontality

According to this principle, sediments are deposited in the horizontal or nearly horizontal layers.

Talus

Accumulation of coarse, angular rock fragments at the base of a slope.

Stratified Drift

Glacial deposits that show both stratification and sorting.

Firn

Granular snow formed by partial melting and refreezing of snow and glacial ice.

Volcanic Tremor

Ground motion lasting for minutes to hours resulting from magma moving beneath the surface, as opposed to the sudden jolts produced by most earthquakes.

Phaneritic Texture

Igneous rock texture in which minerals are easily visible without magnification.

Plutonic (Intrusive Igneous) Rock

Igneous rock that formed from magma intruded into or formed in place within the crust.

Concordant Pluton

Intrusive igneous body whose boundaries parallel the layering in the country rock.

Karst Topography

Landscape consisting of numerous caves, sinkholes, and solution valleys formed by groundwater solution of rocks such as limestone and dolostone.

Nevadan Orogeny

Late Jurassic to Cretaceous deformation that strongly affected the western part of North America.

AA

Lava flow with a surface of rough, angular blocks and fragments.

Strata

Layering in sedimentary rocks.

Sediment

Loose aggregate of solids derived by weathering from preexisting rocks, or solids precipitated from solution by inorganic chemical processes or extracted from solution by organisms.

Lava

Magma that reaches Earth's surface.

Intermediate Magma

Magma with a silica content between 53% to 65% and an overall composition intermediate between mafic and felsic magma.

Ultramafic Magma

Magma with a silica content of less than 45%.

Mafic Magma

Magma with between 45% to 52% silica and proportionately more calcium, iron, and magnesium than intermediate and felsic magma.

Felsic Magma

Magma with more than 65% silica and considerable sodium, potassium, and aluminum, but little calcium, iron, and magnesium.

Compaction

Reduction in the volume of a sedimentary deposit that results from its own weight and the weight of any additional sediment deposited on top of it.

Glaciation

Refers to all aspects of glaciers, including their origin, expansion, and retreat, and their impact on Earth's surface.

Paleomagnetism

Residual magnetism in rocks, studied to determine the rock intensity and direction of Earth's past magnetic field.

Lateral Moraine

Ridge of sediment deposited along the margin of the valley glacier.

Compression

Stress resulting when materials are squeezed by external forces directed toward one another.

Coriolis Effect

The apparent deflection of a moving object from its anticipated course because of Earth's rotation. (Winds and ocean currents are deflected clock wise in the North and counter clockwise in the South)

Luster

The appearance of a mineral in reflected light. (Metallic or non-metallic)

Zone of Saturation

The area below the water table in which all pore spaces are filled with water.

Shoreline

The area between mean low tide and the highest level on land affected by storm waves.

Magnetic Field

The area in which magnetic substances are affected by lines of magnetic force emanating from Earth.

Nearshore Sediment Budget

The balance between additions and losses of sediment in the nearshore zone..

Glacial Budget

The balance between expansion and contraction of glacier in response to accumulation versus wastage.

Silica Tetrahedron

The basic building blocks of all silicate minerals (SiO4).

Wave Refraction

The bending of waves so that they move nearly parallel to the shoreline.

Footwall Block

The block of rock that lies beneath a fault plane.

Hanging Wall Block

The block of rock that overlies a fault plane.

Mohorovicic Discontinuity (Moho)

The boundary between Earth's crust and mantle.

Divergent Plate Boundary

The boundary between two plates that are moving apart.

Convergent Plate Boundary

The boundary between two plates that move toward each other.

Platform

The broad area extending a shield, but covered by younger rocks; a platform and shield from a craton.

Nucleus

The central part of an atom, consisting of protons and neutrons.

Principle of Isostasy

The concept Earth's crust "floating" on a dense underlying layer.

Volcanic Pipe

The conduit connecting the crater of a volcano with an underlying magma chamber.

Hydrologic Cycle

The continuous recycling of water from the oceans, through the atmosphere, to the continents, and back to the oceans, or from the oceans, through the atmosphere, and back to the oceans.

Chemical Weathering

The decomposition of rocks by chemical alteration of parent material.

Wave Base

The depth corresponding to about one-half wavelength, below which water is unaffected by surface waves.

Aphotic Zone

The depth in the ocean below which sunlight does not penetrate.

Strike

The direction of a line formed by the intersection of an inclined plane and a horizontal plane.

Frost Action

The disaggregation of rocks by repeated freezing and thawing of water in creaks and crevasses.

Fetch

The distance the wind blows over a continuous water surface.

Desertification

The expansion of deserts into formerly productive lands.

Canadian Shield

The exposed part of the North American craton; mostly in Canada but also in Minnesota, Wisconsin, Michigan, and New York.

Plastic Flow

The flow that takes place in response to pressure and causes deformation with no fracturing.

Stress

The force per unit area applied to material such as rock.

Core

The interior part of Earth beginning at a depth of 2900 km that probably consists mostly of iron and nickel.

Marine Transgression

The invasion of a coastal area or continent by the sea, resulting from a rise in sea level or subsidence of the land.

Ground Moraine

The layer of sediment released from melting ice as a glacier's terminus retreats.

Regolith

The layer of unconsolidated rock and mineral fragments and soil that covers most of the land surface.

Density

The mass of an object per unit volume; usually expressed in grams per cubic centimeter.

Parent Material

The material that is chemically and mechanically weathered to yield sediment and soil.

Infiltration capacity

The maximum rate at which soil or sediment absorbs water.

Pangea

The name Alfred Wegener proposed for the super-continent consisting of all Earth's landmasses at the end of the Paleozoic Ear.

Atomic Number

The number of protons in the nucleus of an atom.

Atomic Mass Number

The number of protons plus neutrons in the nucleus of an atom.

Zone Wastage

The part of a glacier where losses from melting, sublimation, and calving of icebergs exceed the rate of accumulation.

Dissolved Load

The part of a stream's load consisting of ions in solution.

Bed Load

The part of a stream's sediment load, mostly sand and gravel, transported along its bed.

Zone of Accumulation

The part of glacier where additions exceed losses and the glacier's surface is perennially covered with snow.

Asthenosphere

The part of the mantle that lies below the lithosphere; it behaves plastically and flows slowly.

Porosity

The percentage of a minerals total volume that is pore space.

Isostatic Rebound

The phenomenon in which unloading of the crust causes it to rise until it attains equilibrium.

Magnetic Reversal

The phenomenon involving the complete reversal of the north and south magnet poles.

Columnar Jointing

The phenomenon of forming columns bounded by fractures in some igneous rocks as they cooled and contracted.

Metamorphism

The phenomenon of rocks changing as a result of heat, pressure, and fluids, so that they are in equilibrium with a new set of environmental conditions.

Weathering

The physical breakdown and chemical altercation of rocks and minerals at or near Earth's surface.

Crystal Settling

The physical separation and concentration of minerals in the lower part of magma chamber or pluton by crystallization and gravational settling.

Epicenter

The point on Earth'd surface directly above an earthquakes focus.

Lithification

The process of converting sediment into sedimentary rocks by compaction and cermentation.

Relative Dating

The process of determining the age of an event as compared to other events; involves placing geologic events in their correct chronological order but does not involve the consideration of when the events occurred in number of years ago.

Bonding

The process whereby atoms join other atoms.

Volcanism

The process whereby magma and its associated gases rise through the crust and are extruded onto the surface or into the atmosphere.

Magma Mixing

The process whereby magmas of different composition mix together to yield a modified version of the parent magmas.

Cementation

The process whereby minerals crystallize in the pore spaces of sediment and bind the loose particles together.

Abrasion

The process whereby rock is worn smooth by the impact of sediment transported by running water, glaciers, or wind.

Specific Gravity

The ratio of a substance's weight, especially of a mineral to an equal volume of water at 4 degrees C.

Oxidation

The reaction of oxygen with other atoms to form oxides or, if water is present, hydroxides.

Metamorphic Zone

The region between lines of equal metamorphic intensity known as isograds.

Drainage Patter

The regional arrangement of channels in a drainage system.

Tide

The regular fluctuation of the sea's surface in response to the gravitational attraction of the moon and sun.

Craton

The relatively stable part of a continent; consist of a shield and a buried extension of a shield known as a platform; the ancient nucleus of a continent.

Fossil

The remains of traces of once living organisms.

Hydraulic Action

The removal of loose particles by the power of moving water.

Deflation

The removal of loose surface sediment by wind.

Erosion

The removal of weathered materials from their source area by running water, wind, glaciers, and waves.

Shear Stress

The result of forces acting parallel to one another but in opposite directions; results in deformation by displacement of adjacent layers along closely spaced planes.

Geology

The science concerned with the study of Earth materials (minerals and rocks), surface and internal processes, and Earth history.

Point Bar

The sediment body deposited on the gently sloping side of a meander loop.

Outwash Plain

The sediment deposited by meltwater discharging from a continental glacier's terminus.

Focus

The site within Earth where an earthquake originates and energy is released.

Gradient

The slope of which a stream or river flows.

Upwelling

The slow circulation of ocean water from depth to the surface.

Downwelling

The slow transfer of ocean surface water to depth.

Suspended Load

The smallest particles (silt and clay) carried by running water, which are kept suspended by fluid turbulence.

Atom

The smallest unit of matter that retains the characteristics of an element.

Radioactive Decay

The spontaneous change of an atom to an atom of different element by emission of a particle from its nucleus or by electron capture.

Seismology

The study of earthquakes.

Intensity

The subjective measure of the kind of damage done by an earthquake, as well as people's reaction to it.

Drainage Basin

The surface area drained by a stream or river and its tributaries.

Runoff

The surface flow in streams and rivers.

Water Table

The surface that separates the zone of aeration from the underlying zone of saturation.

Storm Surge

The surge of water onto a shoreline as a result of a bulge in the ocean's surface beneath the eye of a hurricane and wind-driven waves.

Organic Evolution

The theory holding that all living things are related and that they descended with modification from organisms that lived during the past.

Plate Tectonic Theory

The theory holding that large segments of Earth's outer part (lithospheric plates) move relative to one another.

Continental Drift

The theory that the continents were joined into a single landmass that broke apart, with the various fragments moving with respect to one another.

Seafloor Spreading

The theory that the seafloor moves away from spreading ridges and is eventually consumed at subduction zones.

Mantle

The thick layer between Earth's crust and core.

Half-Life

The time necessary for half of the original number of radioactive atoms of an element to decay to a new, and more stable daughter product.

Magnitude

The total amount of energy released by an earthquake at its source.

Photic Zone

The unti layer in the oceans where plants photosynesize.

Discharge

The volume of water in a specific stream or river moving past a specific point in a given interval of time.

Marine Regression

The withdraw of the sea from a continent or coastal area, resulting in the emergence of the land as sea level falls or the land rises with respect to sea level.

Zone of Aeration

The zone above the water table that contains both air and water within the pore space of soil, sediment, or rock.

S-Wave Shadow Zone

Those areas more than 103 degrees from an earthquake focus where no S-waves are recorded.

Groundwater

Underground water stored in the pore spaces of soil, sediment, and rock.

Absolute Dating

Use various radioactive decay dating techniques to assign ages to rocks in years before the present.

Earthquake

Vibrations caused by the sudden release of energy, usually as a result of displacement of rocks along faults.

Glacial Ice

Water in the solid state within a glacier, forms as snow partially melts and refreezes and compacts so that it is transformed first to firm and then to glacial ice.

Ripple Mark

Wavelike structure produced in granular sediment, especially sand, by unidirectional wind and water currents or by oscillating wave currents.

Soil

Weathered materials containing water, air, and humus that can support vegetation.

Differential Weathering

Weathering that occurs at different rates on rocks, thereby yielding an uneven surface.

Kame

Conical hill of stratified drift originally deposited in a depression on a glacier's surface.

Sevier Orogeny

Cretaceous deformation that affected the continental shelf and slope areas of the Cordilleran mobile belt.

Ooze

Deep-sea sediment composed mostly of shells or marine animals and plants.

Strain

Deformation caused by stress.

Correlation

Demonstration of the physical continuity of rock units or biostratigraphic units, or demonstration of time equivalence as in time-stratigraphic correlation.

Mechanical Weathereing

Disaggregation of rocks by physical processes that yields smaller pieces that retain the composition of the parent material.

Lithosphere

Earth's outer, rigid part, consisting of the upper mantle, oceanic crust, and continental crust.

Crust

Earth's outermost layer, and the upper part of the lithosphere; consists of continental and oceanic crust.

Geothermal Gradient

Earth's temperature increase with depth.

Dynamic Metamorphism

Metamorphism in fault zones where rocks are subjected to high differential pressure.

Contact (Thermal) Metamorphism

Metamorphism of country rock adjacent to a pluton.

Regional Metamorphism

Metamorphism that occurs over a large area, resulting from high temperatures tremendous pressure, and the chemical activity of fluids within the crust.

Magma

Molten rock material generated within Earth.

Basal Slip

Movement involving a glacier sliding over its underlying surface.

Continental Accretion

Orogenics along convergent plate boundaries that result in adding material to a continent.

Headland

Part of a shoreline commonly bounded by cliffs that extends out into the sea or a lake.

Hercynian-Alleghenian Orogeny

Pennsylvanian to Permian orogenic event during which the Appalachian mobile belt in eastern North America and the Hercynian mobile belt of southern Europe were deformed.

Plastic Strain

Permanent deformation of a solid of with no failure by fracturing.

Discordant Plunton

Pluton with boundaries that cut across the layering in the country rock.

Lithostatic Pressure

Pressure exerted on rocks by the weight of overlying rocks.

Differential Pressure

Pressure that is not applied equally to all sides of a rock body.

Graded Bedding

Sedimentary layer in which a single bed shows a decrease in grain size from bottom to top.

Chemical Sedimentary Rock

Sedimentary rock made up of minerals that were dissolved during chemical weathering and later precipitated from seawater, or extracted from solution by organisms.

Detrital Sedimentary Rock

Sedimentary rock made up of the solid particles (detrius) of preexisting rocks.

Loess

Wind blown deposits of silt and clay.