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WGU SEA4 Geology

WGU SEA4 Geology Terms

Mineral Any naturally occurring inorganic solid that possesses an orderly crystalline structure and a definite chemical composition
Rock Any solid mass of mineral, or mineral-like, matter that occurs naturally as part of our planet
Aggregate Minerals joining in a way that the rock retains all of the properties of each mineral
Element A substance that can not be broken down into simpler substances by chemical or physical means
Periodic Table The tabular arrangement of the elements according to atomic number
Nucleus The small heavy core of an atom that contains all of its positive change and most of its mass.
Proton A positively charged subatomic particle found in the nucleus of an atom
Neutron A subatomic particle found in the nucleus of an atom. It is electrically neutral and has a mass approximately that of a proton.
Electron A negatively charge subatomic particle that has a negligible mass and is found outside an atom's nucleus
Principal Shell Energy Levels
Energy Levels Spherically shaped negatively changed zones that surround the nucleus of an atom.
Valence Electrons The electrons involved in the bonding process; the electrons occupying the highest principal energy level of an atom
Atomic Number The number of protons in the nucleus of an atom.
Mass Number The number of neutrons and protons in the nucleus of an atom
Radioactive Decay
Compound A substance formed by the chemical combination of two or more elements in definite proportions and usually having properties different from those of its constituent elements.
Ionic Bond A chemical bond between oppositely charged ions formed by the transfer of valence electrons from one atom to another.
Covalent Bond A chemical bond produced by the sharing of electrons
Ions An atom or molecule that posses an electrical charge
Crystal Form The external appearance of a mineral as determined by its internal arrangement of atoms
Luster The appearance or quality of light reflected from the surface of a mineral
Streak The color of a mineral in powdered form
Hardness The resistance a mineral offers to scratching
Moh's Scale A series of 10 minerals used as a standard in determining hardness
Cleavage The tendency of a mineral to break along planes of weak bonding
Fracture Any break or rupture in rock along which no appreciable movement has taken place
Specific Gravity The ratio of a substance's weight to the weight of an equal volume of water
Carbonates Mineral group whose members contain the carbonate ion (CO2 -2) and one or more kinds of positive ions.
Rock-Forming Minerals A classification of minerals that make up the Earth's crust
Nonsilicates Any mineral that does not fall into the silicates group
Silicon-Oxygen Tetrahedron A structure composed of 4 oxygen atoms surrounding a silicon atom that constitutes the basic building block of silicate minerals.
Feldspars A largest group of minerals
Quartz A second most abundant mineral group
Mineral Resource All discovered and undiscovered deposits of a useful mineral that can be extracted now or at some time in the future
Reserves Already identified deposits from which minerals can be extracted profitably
Andesitic composition The composition of igneous rocks lying between felsic and mafic
Basaltic composition A compositional group of igneous rocks indicating that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar
Bowen’s reaction series A concept that illustrates the relationships between magma and the minerals crystallizing from it during the formation of igneous rocks
Chemical sedimentary rocks Sedimentary rock consisting of material that was precipitated from water by either inorganic or organic means
Coarse-grained texture An igneous rock texture in which the crystals are roughly equal in size and large enough so that individual minerals can be identified with the unaided eye
Contact metamorphism Changes in rock caused by the heat from a nearby magma body
Crystallization The formation and growth of a crystalline solid from a liquid or gas
Crystal Settling During the crystallization of magma, the earlier-formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber
Detrital sedimentary rock Rock formed from the originated and was transported in the form of solid particles derived from both mechanical and chemical weathering
Disseminated deposit Any economic mineral deposit in which the desired mineral occurs as scattered particles in the rock but in sufficient quantity to make the deposit an ore
Evaporite A sedimentary rock formed of material deposited from solution by evaporation of the water
Extrusive (volcanic) Igneous activity that occurs outside the crust
Felsic The group of igneous rocks composed primarily of feldspar and quartz
Fine-Grained Texture A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished with
Fossils The remains or traces of organisms preserved from the geologic past
Foliated A texture of metamorphic rocks that gives the rock a layered appearance
Glassy A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals
Granitic composition A compositional group of igneous rocks that indicates a rock is composed almost entirely of light-colored silicates.
Hydrothermal solution the hot, watery solution that escapes from a mass of magna during the later stages of crystallization. It may alter the surrounding country rock and are frequently the source of significant ore deposits
Igneous Rock A rock formed by the crystallization of molten magma
Intermediate composition The composition of igneous rocks lying between felsic and mafic
Intrusive (plutonic) Igneous rock that formed below the Earth’s surface
Lava Magma that reaches the Earth’s surface
Lithification The process, generally cementation and/or compaction, of converting sediments to solid rock
Mafic Igneous rocks with a low silica content and a high iron-magnesium content
Magma A body of molten rock found at depth, including any dissolved gases and crystals
Magmatic Differentiation The process of generating more than one rock type from a single magma
Metamorphic Rock Rocks formed by the alteration of preexisting rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids
Metamorphism The changes in mineral composition and texture of a rock subjected to high temperature and pressure within Earth
Nonfoliated Metamorphic rocks that do not exhibit foliation
Pegmatite A very coarse-grained igneous rock (typically granite) commonly found as a dike associated
Porphyritic Material The volcanic rock ejected during an eruption, including ash, bombs or blocks
Regional metamorphism Associated with large-scale mountain-building processes
Rock cycle A model that illustrates the origin of the three basic rock types and the interrelatedness of Earth materials and processes
Sediment Unconsolidated particles created by the weathering and erosion of rock, by chemical precipitation from solution in water, or from the secretions of organisms and transported by water, wind or glaciers
Sedimentary Rock Rock formed from the weathered products of preexisting rocks that have been transported, deposited and lithified
Strata Parallel layers of sedimentary rock
Texture The size, shape, and distribution of the particles that collectively constitute a rock.
Thermal Metamorphism Changes in rock caused by the heat from a nearby magma body
Ultramafic Igneous rocks composed mainly of iron and magnesium-rich minerals
Vein deposit A mineral filling a fracture or fault in a host rock. Such deposits have a sheetlike, or tabular, form
Contact metamorphism Changes in rock caused by the heat from a nearby magma body
Atom The smallest particle that exists as an element
Color A diagnostic observation in mineral classification. Is not as reliable as streak for determination.
Isotope Varieties of the same element that have different mass numbers; their nuclei contain the same number of protons but different numbers of neutrons.
Ore Usually a useful metallic mineral that can be mined for a profit. The term is also applied to certain non-metallic minerals such as fluorite and sulfur.
Silicate Any one of numerous minerals that have the oxygen and silicon tetrahedron as their basic structure.
Angular Unconformity An unconformity in which the strata below dip at an angle different from that of the beds above.
Catastrophism The concept that Earth was shaped by catastrophic events of a short-term nature.
Cenozoic Era A span of the geologic time scale beginning about 65 million years ago following the Mesozoic Era.
Conformable Layers of rock that were deposited without interruption.
Correlation Establishing the equivalence of rocks of similar age in different areas.
Cross-Cutting Relationship A principle of relative dating. A rock or fault is younger than any rock (or fault) through which it cuts.
Disconformity A type of unconformity in which the beds above and below are parallel.
Eon The largest time unit on the geologic time scale, next in order of magnitude above era.
Epoch A unit of the geologic calendar that is a subdivision of a period.
Era A major division on the geologic calendar; they are divided into shorter units called periods.
Fossil The remains or traces of organisms preserved from the geologic past.
Fossil Succession Fossil organisms that succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content.
Geologic Time Scale The division of Earth history into blocks of time - eons, eras, periods and epochs. The time scale was created using relative dating principles.
Half-Life The time required for one half of the atoms of a radioactive substance to decay.
Inclusions A piece of one rock unit contained within another. They are used in relative dating. The rock mass adjacent to the one containing it must have been there first in order to provide the fragment.
Index Fossil A fossil that is associated with a particular span of geologic time.
Mesozoic Era A span on the geologic time scale between the Paleozoic and Cenozoic eras from about 248 million to 65 million years ago.
Nonconformity An unconformity in which older metamorphic or intrusive igneous rocks are overlain by younger sedimentary strata.
Numerical Date Date that specifies the actual number of years that have passed since an event occurred.
Original Horizonality Layers of sediments are generally deposited in a horizontal or nearly horizontal position.
Paleontology The systematic study of fossils and the history of life on Earth.
Paleozoic Era A span on the geologic time scale between the eons of the Precambrian and Mesozoic era from about 540 million to 248 million years ago.
Period A basic unit of the geologic calendar that is a subdivision of an era. They may be divided into smaller units called epochs.
Phanerozoic Era That part of geologic time represented by rocks containing abundant fossil evidence. The eon extending from the end of the Proterozoic eon (about 540 million years ago) to the present.
Precambrian All geologic time prior to the Paleozoic Era.
Radioactivity The spontaneous decay of certain unstable atomic nuclei.
Radiocarbon (carbon-14) The radioactive isotope of carbon, which is produced continuously in the atmosphere and is used in dating events from the very recent geologic past (the last few tens of thousands of years).
Radiometric Dating The procedure of calculating the absolute ages of rocks and minerals that contain radioactive isotopes.
Relative Dating Rocks are placed in their proper sequence or order. Only the chronological order of events is determined.
Law of Superposition In any undeformed sequence of sedimentary rocks, each bed is older than the layers above and younger than the layers below.
Unconformity A surface that represents a break in the rock record, caused by erosion or non deposition.
Uniformitarianism The concept that the processes that have shaped Earth in the geologic past are essentially the same as those operating today.
Outgassing The escape of gases that had been dissolved in magma.
Shields A large, relatively flat expanse of ancient metamorphic rock within the stable continental interior.
Stromatolites Structures that are deposited by algae and consists of layered mounts of calcium carbonate.
Angle of Repose The steepest angle at which loose material remains stationary without sliding downslope.
Chemical Weathering The processes by which the internal structure of a mineral is altered by the removal and/or addition of elements.
Creep The slow downhill movement of soil and regolith.
Debris Flow A relatively rapid type of mass wasting that involves a flow of soil and regolith containing a large amount of water
Differential Weathering The variation in the rate and degree of weathering caused by such factors as mineral makeup, degree of jointing, and climate.
Earthflow The downslope movement of water-saturated, clay-rich sediment. Most characteristic of humid regions.
Eluviation The washing out of fine soil components from the A horizon by downward percolating water.
Erosion The incorporation of transportation of material by a mobile agent, such as water, wind or ice.
Exfoliation Dome Large, dome-shaped structure, usually composed of granite, formed by sheeting.
External Processes Process such as weathering, mass wasting or erosion that is powered by the Sun and transforms solid rock into sediment.
Fall A type of movement common to mass-wasting processes that refers to the free falling of detached individual pieces of any size.
Flow A type of movement common to mass-wasting processes in which water-saturated material moves downslope as a viscous fluid.
Frost Wedging The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices.
Horizon A layer in a soil profile.
Internal Processes These derive their energy from Earth's interior.
Lahar Mudflows on the slopes of volcanoes the result when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels.
Leaching The depletion of soluble materials from the upper soil by downward-percolating water.
Mass Wasting The downslope movement of rock, regolith, and soil under the direct influence of gravity.
Mechanical Weathering The physical disintegration of rock, resulting in smaller fragments.
Parent Material The material upon which a soil develops.
Permafrost Refers to the permanently frozen ground that occurs in Earth's harsh tundra and ice-cap climates.
Regolith the layer of rock and mineral fragments that nearly everywhere covers Earth's surface.
Rockslide The rapid slide of a mass of rock downslope along planes of weakness.
Secondary Enrichment the concentration of minor amounts of metals that are scattered through unweathered rock into economically valuable concentrations by weathering processes.
Sheeting A mechanical weathering process characterized by the splitting off of slablike sheets of rocks.
Slide A movement common to mass-wasting processes in which the material moving downslope remains fairly coherent and moves along a well-defined surface.
Slump The downward slipping of a mass of rock or unconsolidated material moving as a unit along a curved surface.
Soil A combination of mineral and organic matter, water, and air; that portion of the regolith that supports plant growth.
Soil Profile A vertical section through a soil showing its succession of horizons and the underlying parent material.
Soil Taxonomy A soil classification system consisting of six hierarchical categories based on observable soil characteristics. The system recognizes 12 soil orders.
Soil Texture The relative proportions of clay, silt, and sand in soil. It strongly influences the soil's ability to retain and transmit water and air.
Solifluction Slow, downslope flow of water-saturated materials common to permafrost areas.
Solum The O, A, and B horizons in a soil profile. Living roots and other plant and animal life are largely confined to this zone.
Sperodial Weathering When the weathered rock has a more rounded or spherical shape.
Talus Slope An accumulation of rock debris at the base of a cliff.
Weathering The disintegration and decomposition of rock at or near Earth's surface.
External Processes Weathering, mass wasting and erosion are examples because they occur at or near the Earth's surface and are powered by the Sun.
Alluvial Fan A fan-shaped deposit of sediment formed when a stream's slope is abruptly reduced.
Alluvium Unconsolidated sediment deposited by a stream
Aquifer Rock or soil through which groundwater moves easily.
Aquitard Impermeable beds that hinder or prevent groundwater movement.
Artesian Well A well in which the water rises above the level where it was initially encountered.
Backswamp A poorly drained area on a floodplain that results when natural levees are present.
Bar Common term for sand and gravel deposits in a stream channel.
Base Level The level below which a stream cannot erode.
Bed Load Sediment that is carried by a stream along the bottom of its channel.
Braided Stream A stream consisting of numerous intertwining channels.
Capacity The total amount of sediment a stream is able to transport.
Cavern A naturally formed underground chamber or series of chambers most commonly produced by solution activity in limestone.
Competence A measure of the largest particle a stream can transport; a factor dependent on velocity.
Cone of Depression A cone-shaped depression in the water table immediately surrounding a well.
Cutoff A short channel segment created when a river erodes through the narrow neck of land between meanders.
Delta An accumulation of sediment formed where a stream enters a lake or ocean
Dendritic Pattern A stream system that resembles the pattern of a branching tree.
Discharge The quantity of water in a stream that passes a given point in a period of time.
Dissolved Load That portion of a stream's load carried in solution.
Distributary A section of a stream that leaves the main flow.
Divide An imaginary line that separates the drainage of two streams; often found along a ridge.
Drainage Basin The land area that contributes water to a stream.
Drawdown The difference in height between the bottom of a cone of depression and the original height of the water table.
Evapotranspiration The combined effect of evaporation and transpiration.
Flood When the discharge of a stream becomes so great that it exceeds the capacity of its channel.
Floodplain The flat, low-lying portion of a stream valley subject to periodic inundation.
Geyser A fountain of hot water ejected periodically.
Gradient The slope of a stream; generally measured in feet per mile.
Groundwater Water in the zone of saturation.
Hot Spring A spring in which the water is 6-9 degrees Celsius (10 -15 degrees Fahrenheit) warmer than the mean annual air temperature of the locality.
Hydrologic Cycle The unending circulation of Earth's water supply.
Incised Meander Meandering channel that flows in a steep, narrow valley; They form either when an area is uplifted or when base level drops.
Infiltration The movement of surface water into rock or soil through cracks and pore spaces.
Karst A topography consisting of numerous depressions called sinkholes.
Laminar Flow The movement of water particles in straight-line paths that are parallel to the channel. The water particles move downstream without mixing.
Meander A looplike bend in the course of a stream.
Natural Levee The elevated landforms that parallel some streams and act to confine their waters, except during floodstage.
Oxbow Lake A curved lake produced when a stream cuts off a meander.
Permeability A measure of a material's ability to transmit water.
Porosity The volume of open spaces in rock or soil.
Radial Pattern A system of streams running in all directions away from a central elevated structure, such as a volcano.
Rectangular Pattern A drainage pattern characterized by numerous right-angle bends that develops on jointed or fractured bedrock.
Runoff Water that flows over the land rather than infiltrating into the ground.
Sinkhole (Sink) A depression produced in a region where soluble rock has been removed by groundwater.
Sorting The process by which solid particles of various sizes are separated by moving water or wind. Also, the degree of similarity in particle size in sediment or sedimentary rock.
Spring A flow of groundwater that emerges naturally at the ground surface.
Stalactite The icicle-like structure that hangs from the ceiling of a cavern.
Stalagmite The column-like form that grows upward from the floor of a cavern.
Stream Valley Consists not only of the channel but also the surrounding terrain that directly contributes water to the stream.
Suspended Load The fine sediment carried withing the body of flowing water.
Transpiration The release of water vapor to the atmosphere by plants.
Trellis Pattern A system of streams in which nearly parallel tributaries occupy valleys cut in folded strata.
Turbulent Flow The movement of water in an erratic fashion often characterized by swirling, whirlpool-like eddies. Most streamflow is of this type.
Water Table The upper level of saturated zone of groundwater.
Well An opening bored into the zone of saturation.
Yazoo Tributary A tributary that flows parallel to the main stream because a natural levee is present.
Zone of Aeration Area above the water table where openings in the soil, sediment, and rock are not saturated but filled mainly with air.
Zone of Saturation Zone where all open spaces in sediment and rock are completely filled with water.
Aftershock Smaller earthquakes that follow the main earthquake.
Asthenosphere A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers and in some regions extends as deep as 700 kilometers. The rock within this zone is easily deformed.
Body Wave Seismic waves that travel through Earth's interior.
Core Located beneath the mantle, it is the innermost layer of Earth. The core is divided into an outer core and an inner core.
Crust The very thin outermost layer of Earth.
Earthquake The vibration of Earth produced by the rapid release of energy.
Elastic Rebound The sudden release of stored strain in rocks that results in movement along a fault.
Epicenter The location on Earth's surface that lies directly above the focus of an earthquake.
Fault A break in a rock mass along which movement has occurred.
Fault Creep Displacement along a fault that is so slow and gradual that little seismic activity occurs.
Focus The zone within Earth where rock displacement produces an earthquake.
Foreshock Small earthquakes that often precede a major earthquake.
Inner Core The solid innermost layer of Earth, about 1300 kilometers (800 miles) in radius.
Intensity A measure of the degree of earthquake shaking at a given locale based on the amount of damage.
Liquefaction A phenomenon, sometimes associated with earthquakes, in which soils and other unconsolidated materials containing abundant water are turned into a fluidlike mass that is not capable of supporting buildings.
Lithosphere The rigid outer layer of Earth, including the crust and upper mantle.
Magnitude The total amount of energy released during an earthquake.
Mantle The 2,900 kilometer (1,800 miles) thick layer of Earth located below the crust.
Mesosphere The layer of the atmosphere immediately above the stratosphere and characterized by decreasing temperatures with height.
Lower Mantle The layer of the atmosphere immediately above the stratosphere and characterized by decreasing temperatures with height.
Modified Mercalli Intensity Scale A 12 point scale developed to evaluate earthquake intensity based on the amount of damage to various structures.
Mohorovicic Discontinunity (Moho) The boundary separating the crust from the mantle, discernible by an increase in seismic velocity.
Moment Magnitude A more precise measure of earthquake magnitude than the Richter scale that is derived from the amount of displacement that occurs along a fault zone.
Outer Core A layer beneath the mantle about 2,200 kilometers (1,364 miles) thick that has the properties of liquid.
Primary (P) Wave A type of seismic wave that involves alternating compression and expansion of the material through which it passes.
Richter Scale A scale of earthquake magnitude based on the motion of a seismograph.
Secondary (S) Wave A seismic wave that involves oscillation perpendicular to the direction of propagation.
Seismic Sea Wave (Tsunami) A rapidly moving ocean wave generated by earthquake activity capable of inflicting heavy damage in coastal regions.
Seismogram The record made by a seismograph.
Seismology The study of earthquakes and seismic waves.
Shadow Zone The zone between 104 and 143 degrees distance from an earthquake epicenter in which direct waves do not arrive because of refraction by Earth's core.
Surface Wave Seismic waves that travel along the outer layer of Earth.
Asthenosphere A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers and in some regions extends as deep as 500 kilometers. The rock within this zone is easily deformed.
Continental Drift Theory A theory that originally proposed that the continents are rafted about. It has essentially been replaced by the plate tectonics theory.
Convergent Boundary A boundary in which two plates move together, causing one of the slabs of lithosphere to be consumed into the mantle as it descends on an overriding plane.
Curie Point The temperature above which a material loses its magnetization.
Deep-Ocean Trench An elongated depression in the seafloor produced by bending of oceanic crust during subduction.
Divergent Boundary A region where the rigid plates are moving apart, typified by the mid-oceanic ridges.
Fossil Magnetism i
Fracture Any break or rupture in rock along which no appreciable movement has taken place.
Hot Spot A concentration of heat in the mantle capable of producing magma, which in turn extrudes onto Earth's surface. The intraplate volcanism that produced the Hawaiian Islands is one example.
Lithosphere The rigid outer layer of Earth, including the crust and upper mantle.
Magnetic Reversal
Magnetic Time Scale
Mantle Plume A mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core-mantle boundary.
Normal Polarity A magnetic field that is the same as that which exists at present.
Oceanic Ridge System A continuous elevated zone on the floor of all the major ocean basins and varying in width from 500 to 5000 kilometers (300 to 3000 miles). The rifts at the crests of ridges represent divergent plate boundaries.
Pangaea The proposed supercontinent that 200 million years ago began to break apaer and from the present landmasses.
Partial Melting The process by which most igneous rocks melt. Since individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occured, a melt with hig
Plate One of numerous rigid sections of the lithosphere that moves as a unit over the material of the asthenosphere.
Plate Tectonics The theory that proposes that Earth's outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains & the crust itself.
Reverse Polarity A magnetic field opposite to that which exists at present.
Ridge Push A mechanism that may contribute to plate motion. It involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity.
Rift Zone A region of Earth's crust along which divergence is taking place.
Seafloor Spreading The process of producing new seafloor between two diverging plates.
Slab Pull A mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and "pulls" the trailing lithosphere along.
Slab Suction
Subduction Zone A long, narrow zone where one lithospheric plate descends beneath another.
Transform Fault Boundary A boundary in which two plates slide past one another without creating or destroying lithosphere.
Volcanic Island Arc A chain of volcanic islands generally located a few hundred kilometers from a trench where active subduction of one oceanic slab beneath another is occurring
AA Flow A type of lava flow that has a jagged blocky surface.
Batholith A large mass of igneous rock that formed when magma was emplaced at depth, crystallized and subsequently exposed by erosion.
Caldera A large depression typically caused by collapse or ejection of the summit area of a volcano.
Cinder Cone A rather small volcano built primarily of pyroclastics ejected from a single vent.
Columnar Joint A pattern of cracks that form during cooling of molten rock to generate columns that are generally six sided.
Composite Cone A volcano composed of both lava flows and pyroclastic material.
Conduit A pipelike opening through which magma moves toward Earth's surface. It terminates at a surface opening called a vent.
Continental Volcanic Arc Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent.
Crater The depression at the summit of a volcano, or that which is produced by a meteorite impact.
Decompression Melting Melting that occurs as rock ascends due to a drop in confining pressure.
Dike A tabular-shaped intrusive igneous feature that cuts through the surrounding rock.
Fissure A crack in rock along which there is a distinct separation.
Fissure Eruption An eruption in which lava is extruded from narrow fractures or cracks in the crust.
Flood Basalt Flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of meters.
Furmarole A vent in a volcanic area from which fumes or gases escape.
Geothermal Gradient The gradual increase in temperature with depth in the crust. The average is 30°C per kilometer in the upper crust.
Hot Spot A concentration of heat in the mantle capable of producing magma, which in turn extrudes onto Earth’s surface. The intraplate volcanism that produced the Hawaiian islands is one example.
Intraplate Volcanism Igneous activity that occurs within a tectonic plate away from plate boundaries.
Laccolith A massive igneous body intruded between preexisting strata.
Lahar Mudflows on the slopes of volcanoes that result when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels.
Mantle Plume A mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core–mantle boundary.
Nuee Ardente Incandescent volcanic debris buoyed up by hot gases that moves downslope in an avalanche fashion.
Pahoehoe Flow A lava flow with a smooth-to-ropey surface.
Parasitic Cone A volcanic cone that forms on the flank of a larger volcano.
Partial Melting {most igneous rocks} Individual minerals have different melting points, most igneous rocks melt over temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results.
Pipe A vertical conduit through which magmatic materials have passed.
Pluton A structure that results from the emplacement and crystallization of magma beneath the surface of Earth. Also known as an intrusion.
Pyroclastic Flow A highly heated mixture, largely of ash and pumice fragments, traveling down the flanks of a volcano or along the surface of the ground.
Pyroclastic Materials The volcanic rock ejected during an eruption, including ash, bombs, and blocks.
Scoria Cone A rather small volcano built primarily of pyroclastics ejected from a single vent. Also known as a "cinder cone".
Shield Volcano A broad, gently sloping volcano built from fluid basaltic lavas.
Sill A tabular igneous body that was intruded parallel to the layering of preexisting rock.
Stratovolcanoes A volcano composed of both lava flows and pyroclastic material. Also known as a "composite cone".
Vent The surface opening of a conduit or pipe.
Viscosity A measure of a fluid’s resistance to flow.
Volatiles Gaseous components of magma dissolved in melt. Volatiles readily vaporize (form a gas) at surface pressures.
Volcanic Neck An isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano. Also known as a plug.
Accretionary Wedge A large wedge-shaped mass of sediment that accumulates in subduction zones. Here, sediment is scraped from the subducting oceanic plate and accreted to the overriding crustal block.
Active Continental Margin A portion of the seafloor adjacent to the continents that is usually narrow and consisting of highly deformed sediments. These margins occur where oceanic lithosphere is being subducted beneath the margin of a continent.
Anticline A fold in sedimentary strata that resembles an arch; the opposite of syncline.
Basin A circular downfolded structure.
Brittle Failure
Brittle Deformation Deformation that involves the fracturing of rock. Associated with rocks near the surface.
Deformation General term for the processes of folding, faulting, shearing, compression, or extension of rocks as the result of various natural forces.
Dip-Slip Fault A fault in which the movement is parallel to the dip of the fault.
Dome A roughly circular upfolded structure similar to an anticline.
Ductile Deformation A type of solid state flow that produces a change in the size and shape of a rock body without fracturing. Occurs at depths where temperatures and confining pressures are high.
Fault A break in a rock mass along which movement has occurred.
Fault Block Mountain A mountain formed by the displacement of rock along a fault.
Fault Scarp A cliff created by movement along a fault. It represents the exposed surface of the fault prior to modification by weathering and erosion.
Fold A bent rock layer or series of layers that were originally horizontal and subsequently deformed.
Grabben A valley formed by the downward displacement of a fault-bounded block.
Gravitational Collapse The gradual subsidence of mountains caused by lateral spreading of weak material located deep within these structures.
Horst An elongated, uplifted block of crust bounded by faults.
Isostasy The concept that Earth’s crust is floating in gravitational balance on the material of the mantle.
Isostatic Adjustment Compensation of the lithosphere when weight is added or removed. When weight is added, the lithosphere responds by subsiding, and when weight is removed, there is uplift.
Joint A fracture in rock along which there has been no movement.
Monocline A one-limbed flexure in strata. The strata are unusually flat-lying or very gently dipping on both sides of the monocline.
Normal Fault A fault in which the rock above the fault plane has moved down relative to the rock below.
Orogenesis The processes that collectively result in the formation of mountains.
Passive Continental Margin A margin that consists of a continental shelf, continental slope, and continental rise. These margins are not associated with plate boundaries and therefore experience little volcanism and few earthquakes.
Reverse Fault A fault in which the material above the fault plane moves up in relation to the material below.
Strike-Slip Fault A fault along which the movement is horizontal.
Syncline A linear downfold in sedimentary strata; the opposite of anticline.
Terrane A crustal block bounded by faults, whose geologic history is distinct from the histories of adjoining crustal blocks.
Thrust Fault A low-angle reverse fault.
Transform Fault A major strike-slip fault that cuts through the lithosphere and accommodates motion between two plates.
Created by: MStrange
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