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611 Cards in this Set
- Front
- Back
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Aa
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A type of lava flow that has a jagged, blocky surface.
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Ablation
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A general term for the loss of ice and snow from a glacier
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Abrasion
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The grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, or ice.
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Abyssal plain
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Very level area of the deep-ocean floor, usually lying at the foot of the continental rise
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Accretionary Wedge
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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 bloc.
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Active continental margin
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usually narrow and consisting of highly deformed sediments. They occur where oceanic lithoshpere is being subducted benearth the margin of a continent
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Active layer
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The zone above the permafrost that thaws in summer and refreezes in winter.
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Aftershock
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A smaller earthquake that follows the main earthquake
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Alluvial Fan
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a fan-shaped deposit of sediment formed when a stream's slope is abruptly reduced
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Alluvium
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unconsolidated sediment deposited by a stream
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Andesitic
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Igneous rocks having a mineral makeup between that of grante and basalt, after the common volcanic rock andesite
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Angle of repose
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the steepest angel at which loose material remains stationary without sliding downslope
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Angular unconformity
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An unconformity in which the older strata dip at an angle different from that of the younger beds
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Anthracite
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a hard, metamorphic form of coal that burns clean and hot.
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Anticline
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a fold in sedimentary strata that resembles an arch
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Aphanitic Texture
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a texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished with the unaided eye.
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Aquifer
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rock or sediment through which groundwater moves easily
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Aquitard
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an impermeable bed that hinders or prevents groundwater movement
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Archean eon
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the second eon of Precambrian time. The eon following the Hadean eon and preceding the Proterozoic eon. IT extends between about 3.8 and 2.5 billion years ago.
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Arete
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A narrow, knifelike ridge separating two adjacent glaciated valleys.
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Arkose
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A feldspar-righ sandstone
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Artesian Well
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a well in which the water rises above the level where it was initially encountered.
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Astenosphere
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A subdivision of the mantle situatied 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
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Atmoshpere
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The gasous portion of a plante; the planet's enevelope of air. One of the traditional subdivisions of Earth's physical environment
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Atoll
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A continuous or broken ring or coral reef surrounding a central lagoon
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Atom
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the smallest particle that exists as an element
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Atomic mass unit
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A mass unit equal to exactly one-twelfth the mass of a carbon-12 atom
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Atomic number
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the number of protons in the nucleus of an atom
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Atomic Weight
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the average of the atomic masses of isotopes in a give element
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Aureole
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a zone or halo of contact metamorphism found in the host rock surrounding an igneous intrusion
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Back swamp
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a poorly drained area on a floodplain, resulting when natural levees are present
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Bar
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common term for sand and gravel deposits in a stream channel
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Barchan dune
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a solitary sand dune shaped like a crescent with its tips pointed downwind
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Barchanoid dunes
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dunes forming scalloped rows of sand oriented at right angles to the wind. This form is intermediate between isolated barchans and extensive waves of transverse dunes
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Barrier island
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a low, elongated ridge of sand that parallels the coast
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Basal slip
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a mechanism of glacial movement in which the ice mass slides over the surface below
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basalt
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an aphanitic igneous rock of mafic composition
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basaltic
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term used to describe igneous rocks that contain abundeant dark (ferromagnesian) minerals and about 50 percent silica
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Base level
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the level below which a stream cannot erode
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Basin
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a circular downfolded structure
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Batholith
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a large mass of igneous rock that formed when magma was emplaced at depth, crystallized, and was subsequently exposed by erosion
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Baymouth Bar
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a sandbar that completely crosses a bay, sealing it off from the main body of water
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Beack drift
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the transport of sediment in a zigzag pattern along a becak. It is caused by the uprush of water form obliquely breaking waves
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Beach nourishment
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large quantities of sand are added to the beach system to offset losses caused by wave erosion. By building beaches seaward, becah quality and storm protection are both improved.
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Bedding plane
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a nearly flat surface separating two beds of sedimentary rock. Each bedding plane marks the end of one deposit and the beginning of another having different characteristics.
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Bed load
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sediment rolled along the bottom of a stream by moving water, or particles robed along the ground surface by wind
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Belt of soil moisture
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a zone in which water is held as a film on the surface of soil particles and may be used by plants or withdrawwn by evaporation. The uppermost subdivision of the zone of aeration.
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Biochemical
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describing a type of chemical sediment that form swhen material dissolved is water is precipatead by water-dwelling organisms. Shells are common examples
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Biogenous sediment
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seafloor sediments consisting of material or marine-organic origin
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Bituminous coal
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the most common form of coal, ofter called soft, black coal
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blowout (deflation hollow)
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a depression excavated by wind in easily eroded materials
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body wave
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a seismic wave that travels through Earth's interior
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bottomset bed
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alayer of fine sediment deposited beyond the advancing edge of a delta and then buried by continuous delta growth
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Bowen's reaction series
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a concept proposted by N.L. Bowen that illustrates the relationship between magma and the minerals crystallizing from it during the formation of igneous rock
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Braided stream
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a stream consisting of numerous intertwining channels
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breakwater
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a structure protecting a nearshore area from breaking wave
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Breccia
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a sedimentary rock composed of angular fragments that were lithifiedq
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Brittle deformation
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deformation that in volves the fracturing of rock Associated with rocks near the surface
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Burial metamorphism
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low-grade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata
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Caldera
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a large depression typically caused by collapse of the summit area of a volcano following a violent eruption
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Caliche
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a hard layer, rich in calcium carbonate, that forms beneath the B horizon in soils of arid regions
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Calving
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wastage of a glacier that occurs when large pieces of ice break off into water
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Capacity
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the total amount of sediment a stream is able to transport
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Capillary fringe
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a relatively narrow zone at the base of the zone or aeration. Here water rises from the water table in tiny threadlike openings between grains of soil or sediment.
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Cap rock
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a necessary part of an oil trap. The cap rock is impermeable and hence keeps upwardly mobile oil and gas from escaping at the surface.
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Catastrophism
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the concept that Earth was shaped by catastrophic events or a short -term nature
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Cavern
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a naturally formed underground chamber or serioes of chambers most commonly prodeuced by solution activity in limestone
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Cementation
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one way in which sedimentary rocks are lithified. As material precipitates from water that percolates through the sediment, open spaces are filled and particles are joined into a solid mass
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Cenozoic era
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a time span on the geologic time scale beginning about 65 million years ago following the Mesozoic era
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Chemical sedimentary rock
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sedimentary rock consisting of material that was precipitated from water by either inorganie or organic means
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Chemical weathering
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the processes by whcih the internal structure of a mineral is altered by the removal and/or addition of elements
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Cinder cone
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a rather small volcano built primarily of pyroclastics ejected from a single vent
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Cirque
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an amphitheater-shpaed basin at the head of a glaciated valley produced by frost wedging and plucking
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Clastic
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a sedimentary rock texture consisting of broken fragments of preexisting rock
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Cleavage
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the tendency of a mineral to break along planes of weak bonding
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Col
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a pass between mountain valleys where the headwalls of two cirques intersect
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Color
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a phenomenon of light by which otherwise identical objects may be differentiated
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Column
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a feature found in cabes that is formed when a stalactite and stalagmite join
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Columnar joints
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a pattern of crack sthat forms during cooling of molten rock to generate columns
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Compaction
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a type of lithification in which the weight of overlying material compresses more deeply buried sediment. It is most important in fine-grained sedimentary rocks such as shale.
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Competence
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a measure of the largest particle a stream can transport; a factor dependent on velocity
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Composite cone
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a volcano composed of both lava flows and proclastic material
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compound
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a substance formed by the chemical combination of tow or more elemetns in definite proportions and usually having properties different from those iof its constituent elements
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Concordant
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a term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock
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Conduit
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a piplike opening through which magma moves toward earth's surface. It terminates at a surface opening called a vent.
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Cone of depression
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a cone-shaped depression immediately surrounding a well
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Confortable layers
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rock layers that were deposited with-out interruption
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conglomerate
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a sedimentary rock consisting of rounded, gravel-size particles
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contact metamorphism
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changes in rock cause by the heat of a nearby magma body
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Continental drift
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a hypothesis, credited largely to Alfred Wegener, that suggested all present continents once existed as a single super continent. Further, beginning about 200 million years ago, the super continent began breaking ionto smaller continents, whcih then drifted to their present positions.
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Continental rise
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the gently sloping surface at the vase of the continental slope
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continental shelf
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the gently sloping submerged portion of the continental margin, extending from the shoreline to the continental slope
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Continental slope
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the steep gradient that leads to the deep ocean floor and marks the seaward edge of the continental shelf
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Continental volcanic arc
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mountains formed in part byt igneous activity associated with the subduction of oceanic lithoshpere beneath a continent. Examples include the Andes and the Cascades.
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Convergent plate boundary
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a boundary in which two plates move together, resulting in oceanic lithoshpere being thrust beneath an overriding plate, eventually to be reabsored into the mantle. IT can also involve the collision of two continental plates to create a mountain syystem
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core
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located beneath the mantle, it is Earth's innermost layer. The core is diveided into an outer core and an inner core.
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Correlation
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establishing the equialence of rocks of similar age in different areas
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Crater
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the depression at the summit of a volcano or that which is produced by a meterorite impcat
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Creep
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the slow downhill moveent of soil and regolith
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Crevasse
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a deep crack in the brittle surface of a glacier
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Cross0bedding
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structure inwhich relatively thin layers are inclined at an angle to the main bedding. Formed by currendts of wind or water.
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Cross-cutting
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a principle of relative dating. A rock or fault is younbger than any rock (or fault) through which it cuts
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crust
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the very thing, outermost layer of earth
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Crystal
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an orderly arrangement of atoms
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Crystal form
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the external appearance of a mineral as determined by its internal arrangement of atoms
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Crystallization
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the formation and growth of a crystalline solid from a liquid or gas
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Curie point
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the temperature above which a material loses its magnetization
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Cut bank
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the area of active erosion on the outside of a meander
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Cutoff
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a short channel segment created when a river erodes through the narrow neck of land between meanders
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Dark Silicate
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silicate minerals containing ions of iron and/or magnesium in their structure. They are dark in color and have a higher specific gravity than nonferromagnesian silcates
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Daughter product
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an isotope resulting from radioactive decay
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Debris flow
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a relatively rapid type of mass wating that involves a flow of soil and regolith containing a large amount of water. Also called mudflows
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Decompression melthing
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melting that occurs as rock ascends due to a drop in confining pressure.
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Deep-focus earthquake
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an earthquake focus at a depth of more than 300 kilometers
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Deep-ocean basin
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the portion of seafloor that lies between the continental margin and the oceanic ridge system. This region comprises almost 30 percent of Earth's surface.
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Deflation
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the lifting and removal of loose material by wind
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Deformation
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general term for the processes of folding, faulthing, shearing, compression, or extension of rocks as the result of various natural forces
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Delta
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an accumultaion of sediment formed where a stream enters a lake of ocean
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Dendritic pattern
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a stream system that resembles the pattern of a branching tree
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Density
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the weight per unit volume of a particular material
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Desert
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one of the two types of dry climate; the of the dry climates
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Desert pavement
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a layer of coarse pebbles and gravel created when wind removes the finer material
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Detachment fault
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a low-angle fault that represents a major boundary between unfaultted rocks below that exhibit brittle deformation via faulting
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Detrital sedimentary rocks
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rocks that form from the accumulation of materials that originate and are transported as solid particles derived from both mechanicla and chemical weathering
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Diagenesis
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a collective term for all the chemical, physical, and biological changes that take place after sediments are deposited and during and after lithifaction
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Dike
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a tabular-shaped intrusive igneous feature that cuts through the surrounding rock
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Dip
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the angle at which a rock layer is inclined from the horizontal. The direction of dip is at a right angle to the strike
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Dip-slip fault
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a fault in which the movement is parallel to the dip of the fault
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Discharge
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the quantity of water in a stream that passes a given point in a given period of time
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Disconformity
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a type of unconformity in which the beds above and below are parallel
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Discontinuity
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a sudden change with depth in one or more of the physical properties of the material making up Earth's interior. The boundary between two dissimilar materials in Earth's interior as determined by the behavior of seismic waves.
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Discordant
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a term used to describe plutons that cut across existing rock structures, such as bedding planes
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Disseminated deposit
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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
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Dissolved load
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the portion of a stream's load carried in solution
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Distributary
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a section of a stream that leaves the main flow
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Diurnal tide
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a tide characterized by a single high and low water height each tidal day
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Dissolved load
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the portion of a stream's load carried in solution
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distributary
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a section of a stream that leaves the main flow
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diurnal tide
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a tide characterized by a single high and low water height each tidal day
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Divergent plate boundary
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a boundary in which two plates move apart, resulting in upwelling of materiial from mantle to create a new sea floor
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Divide
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an imaginary line that seperates the drainage of two streams; often found along a ridge
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dome
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a roughly cicular, upfolded structure
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drainage basin
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the land area that contributes water to a stream
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drawdown
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the difference in height between the bottom of a cone of depression and the original height of the water table
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drawdown
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the difference in height between the bottom of a cone of depression and the original height of the water table
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Drumlin
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a streamlined asymmetrical hill composed of glacial till. The steep side of the hill faces the direction from which the ice advanced
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dry climate
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a climate in which the yearly precipitation is less than the potential loss of water by evaporation
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Ductile deformation
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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 confininf pressures are high
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Dune
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a hill or ridge of wind-deposited sand
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dry climate
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a climate in which the yearly precipitation is less than the potential loss of water by evaporation
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earthflow
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the downslope movement of water-saturated clay-rich sediment. Most characteristic of humid regions.
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earthquake
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vibration of earth produced by the rapid release of energy
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Echo sounder
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an instrument used to determine the depth of water by measuring the time interval between emission of a sound signal and the return of its echo from the bottom
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Elastic deformation
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nonpermanent deformation in which rock returns to its original shape when the stress is released
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Elastic deformation
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nonpermanent deformation in which rock returns to its original shape when the stress is released
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elastic rebound
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the sudden release of stored strain in rocks that results in movement along fault
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electron
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a negatively charged subatomic particle that has negligible mass and is found outside the atom's nucleus
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Element
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a substance that cannot be decomposed into simpler substances by oridnary chemical or physical means
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Emergent Coast
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a coast where land formerly below the sea level has been exposed either by crustal uplift or a drop in sea level of both
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End moraine
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a ridge of till marking a former position of the front of the glacier
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Energy-level shell
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the region occupied by electrons with a specific energy level
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Eon
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the largest time unit of the geologic time scale, next in order of magnitude above is...era
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Epicenter
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the location of Earth's surface that lies directly above the focus of an earthquake
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Epoch
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a unit of the geological time scale that is a subdivision of a period
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Era
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a major division on the geologic time scale; eras are divided into shorter units called periods
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Erosion
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the incorporation and transportation of material by a mobile agent, such as water, wind, or ice
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Eruption column
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buoyant plumes of host ash-laden gases that can extend thousands of meters into the atmosphere
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Esker
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sinuous ridge composed largely of sand gravel deposited by a stream flowing in a tunnel beneath a glacier near its terminus
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Estuary
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a partially enclosed coastal water body that is conneted to the ocean. Salinity here is measurably reduced by the freshwater flows of rivers
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Evaporite
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a sedimentar rock formed of material deposited from solution by evaporation of water
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Evapotranspiration
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the combined effect of evaporation and transpiration
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Exfoliation Dome
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large, dome-shaped structure, usually composed of granite, formed by sheeting
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Exotic stream
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a permanent stream that traverses a desert and has its source in well-watered ares outside the desert
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External process
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process such as weathering, mass wating, or erosion that is powered by the Sun and transforms solid rock into sediment
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Extrusive
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igneous activity that occurs at Earth's surface
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Fall
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a type of movement common to mass0wasting processes that refers to the free falling of detached individual pieces of any size
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Fault
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a break in a rock mass along which movement has occured
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Fault-block mountain
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a mountain formed by the displacement of rock along fault
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Fault creep
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slow, gradula displacement along a fault that occurs relatively smoothly and with little noticeable seismic activity
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Fault scarp
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a cliff created by movement along a fault. It represents the exposed surface of the fault prior to modification by weathering and erosion
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Felsic
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a term derived from feldspar and silica (quartz). It is a term used to describe granitic igneous rocks
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Fetch
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the distance that the wind has traveled across the open water
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Fiord
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a steep-sided inlet of the sea formed when a glacial trough was partially submerged
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Fissure
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a crack in rock along which there is a distinct separation
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Fissure eruption
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an eruption in which lava is extruded from narrow fractures or cracks in the crust
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Flood
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the overflow of a stream channgel that occurs when discharge exceeds the channel's capactiy. The most common and destructive geologic hazard
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Flood basalts
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flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of meters
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Floodplain
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the flat, low-lying prtion of a stream valley subject to periodic inundation
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Flow
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a type of movement common to mass-wasting processes in which water-saturated material moves downslope as a viscous fluid
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Fluorescence
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the absorption of ultraviolet light, which is reemited as visible light
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Fold
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a best layer or series of layers that were originally horizontal and subsequently deformed
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Foliated
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a texture of metamorphic rocks that gives the rock a layered appearance
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Foliation
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a term for a linear arrangement of textural features often exhibited by metamorphic rocks
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foreset bed
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an inclined bed deposited along the front of a delta
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foreshocks
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small earthquakes that often precede a major earthquake
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fossil
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the remains or traces of organisms preserved from the geologic past
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fossil fuel
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general term for any hydrocarbon that may be used as a fossil fuel, including coal, oil, natural gas, bitumen from tar sands, and shale oil
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Fossil succession
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fossil organisms succeed one another in a definite and determinable order, and at any time period can be recognized by its fossil content
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Fractional crystalization
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the process that seperates magma into components having varieds compositions and melting points
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fracture(mineral)
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one of the basic physical properties of minerals It relates to the breakge of mineral when there are no planes of weakness in the crystalline structure. Examples include conchoidal, irregular, and splintery
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Fracture (rock)
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any break or rupture in rock along which no appreciable movement has taken place
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Frost wedging
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the mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices
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Fumarole
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a vent in a volcanic area from which fumes or gases escape
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Gaining stream
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streams that gain water from the inflow of groundwater through the streambed
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Geology
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the science the examines Earth, its form and composition, and the changes it has undergone and is undergoing
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Geothermal Energy
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natural steam used fro power generation
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Geothermal gradient
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the gradual increase in temperature with depth in the crust. The average is 30degrees C per kilometer in the upper crust
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Geyser
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a fountain of hot water ejected periodically from the ground
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Glacial Budget
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the balance, or lack of balance, between accumulation at the upper end of a glacier, and loss at the other end
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Glacial drift
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an all-embracing term for sediments of glacial origin, no matter how, where, or in what shape they were deposited
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Glacial Budget
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the balance, or lack of balance, between accumulation oat the upper end of a glacier, and loss at the other end
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Glacial erratic
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an ice-transported boulder that was not derived from the bedrock near its present site
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Glacial striations
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scratches and grooves on bedrock cuased by glacial abrasion
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Glacial trough
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a mountain valley that has been widened, deepened, and straightened by a glacier
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Glacier
|
a thick mass of ice originating on land from the compaction and recrystallization of snow. The ice shows evidence of past or present flow.
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Glass (volcanic)
|
natural glass produced when molten lava cools too rapidly to permit crystallization. Volcanic glass is a solid composed of unordered atoms
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Glassy texture
|
a term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals
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Gneissic Texture
|
the texture displayed by the metamorphic rock gneiss in which dark and light silicate minerals have separated, giving the rock a banded appearance
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Gondwanaland
|
the southern portion of Pangaea consisting of South America, Africa, Australia, India, and Antartica
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Graben
|
a valley formed by the downward displacement of a fault-bounded block
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Graded bed
|
a sediment layer characterized by a decrease in sediment size from bottom to top
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Graded stream
|
a stream that has the correct channel characterisitcs to maintain the exact velocity required to transport the material supplied to it
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Granitic
|
igneous rocks composed mainly of light coloered silicates (quartz and feldspar) are said to have this composition
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Gradient
|
the slop of a stream; generally measured in feet per mile
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Greenhouse effect
|
carbon dioxide and warer vapor in a planet's atmosphere absorb and reradiate infrared wavelengths, effectibvely trapping solar energy and raising the temperature
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Groin
|
a short wall built at a right angle to the seashore to trap moving sand
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Groundmass
|
the matrix of smaller crystlas within an igneous rock that has porphyritic texture
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Ground moraine
|
an undulating layer of till deposited as the ice front retreats
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Groundwater
|
water in the zone of saturation
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Guyot
|
a submerged flat-topped seamount
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Hadean eon
|
the first eon on the geologic time scale. The eon ending 3.8 billion years ago that preceded the Archean eon
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Half-life
|
the time required for on half of the atoms of a radiocative substance to decay
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Hanging valley
|
a tributary valley that enters a clacial trought at a considerable height above the floor of the trough
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Hardness
|
a mineral's resistance to scratching and abrasion
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head
|
the vertical distance between the recharcge and discharge points of a water table. Also, the source area or beginning of a valley
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Headward erosion
|
the extension upslope of the head of a valley due to erosion
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Historical geology
|
a major division of gelogy that deals with the origin of Earth and its develpment through time. usually involves the study of fossils and their sequence in rock beds.
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Hogback
|
a naroow, sharp-crested ridge formed by the upturned edge of a steeply dipping bed of resistant rock.
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Horn
|
a pyramid-like peak formed by glacial action in three or more cirques surrounding a mountain summit
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Horst
|
an elongated, uplifted block of crust bounded by faults
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Hot spot
|
a proposed concentration of heat in the mantle capable of introducing magma that in turn extrudes onto Earth's surface. The intraplate volcanism that produced the Hawaiian Islands is one exaple.
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Hot spring
|
a spring in which the water is 6-9 degrees C warmer than the mean annual air temperature of its locality
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Humus
|
Organic matter in soil produced by the decomposition of plants and animals
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Hydrogenous sediment
|
seafloor sediments consisting of minerals that crystallize from seawater. The principal example is manganese nodules
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Humus
|
organic matter in soil produced by the decompoistion of plants and animals
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Hydrologic Cycle
|
the unending circulation of Earth's water supply. The cycle is powered by energy from the Sun and is characterized by continuous exchanges of water among the oceans, the atmosphere, annd the continents
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Hydrolisis
|
A chemical-weathering process in which minerals are altered by chemically reacting with water and acids
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Hydrosphere
|
the water portion of our planet; one of the traditional subdivisions of Earth's physical environment
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Hydrosphere
|
the water portion of our planet; one of the traditional subdivisions of Earth's physical environment
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Hydrothermal metamorphism
|
chemical alterations that occur as hot, ion-rich water ciculates through fractures in rock
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Hydrothermal solution
|
the hot, watery soution that escapes from a mass of magma during the latter stages of crystallization. Such solutions may alter the surrounding country rock and are frequently the source of significant ore deposits
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Hypotesis
|
a tentative explanation that is then tested to determine if it is valid
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Ice cap
|
A mass of glacial ice covering a high upland or plateau and spreading out radially
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Ice-contact deposit
|
an accumulation of stratified drift deposited in contact with a supporting mass of ice
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Ice sheet
|
a very large, thick mass of glacial ice flowing outward in all directions from one or more accumulation centers
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Igneous rock
|
a rock formed by the crystallization of molten magma
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Immature Soil
|
a soil lacking horizons
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Impact metamorphism
|
metamorphism that occurs when meterorites strike Earth's surface
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Incised Meander
|
Meandering channel that flows in a steep, narrow valley. These meanders form either when an area is uplifted or when base level drops
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Inclusion
|
a piece of one rock unit contained within another. Inclusions are used in relative dating. The rock mass adjacent to the one containg the inclusion must have been there first in order to provide the fragment
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Index fossil
|
a fossil that is associated with a particular span of geologic time
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Index mineral
|
a mineral that is a good indicator of the metamorphic environemnt in which it formed. Used to distinguish different zones of regional metamorphism
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Inertia
|
objects at rest tent to remain at rest, and objects in motion tend to stay in motion unless either is acted upon by an outside force
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Infiltration
|
the movement of surface water into rock or soil through crack and pore spaces
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Infiltration capacity
|
the maximum rate at which soil can absorb water
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Inner core
|
the solid, innermost layer of Earth, about 1216 kilometers in radius
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Inselberg
|
an isolated mountain remnant characteristic of the late stage of erosion in a mountainous region
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Intensity (earthquake)
|
a measure of the degree of earthquake shaking at a give locale based on the amount of damage
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Interior drainage
|
a discontinuous patter of intermittent streams that do not flow to the ocean
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Intermediate
|
compositional category for igneous rocks found near the middle of Bowen's reaction series, mainly amphibole and the intermediate plagioclase feldspars
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Intermediate focus
|
an earthquake focus at a depth of between 60-300 kilometers
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Internal process
|
a process such as mountain building or volcanism that derives its energy from Earth's interior and elevates Earth's surface
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Intraplate volcanism
|
igneous activity that occurs within a tectonic plate away from plate boundaries
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Intrusive rock
|
Igneous rock that formed below Earth's surface
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Internal process
|
a process such as mountain building or volcanism that derives its energy from Earth's interior and elevates Earth's surface
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Intraplate Volcanism
|
igenous activity that occurs within a tectonic plate away from plate boundaries
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Intrusive rock
|
igneous rock that formed below Earth's surface
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Ion
|
an atom or molecule that possesses an electrical charge
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Ionic bond
|
a chemical bond between two oppositely charged ions formed by the transfer of valance electrons from one atom to another
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Isostasy
|
the concept that Earth's crust is floating in gravitational balance upon the material of the mantle
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Isotopes
|
varieties of the same element that have different mass numbersl their nuclei contain the same number of protons but different number of neutrons
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Joint
|
a fracture in rock along which there has bgeen no movement
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Kame
|
a steep-sided hill composed of sand and gravel originating when sediment collected in openings in stagnant glacial ice
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Kame terrace
|
a narrow, terracelike mass of stratified drift deposited between a glacier and an adjacent valley wall
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Karst
|
a topography consisting of numerous depressions called sinkholes
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Kettle holes
|
depressions created when blocks of ice become lodged in glacial deposits and subsequently melt
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Laccolith
|
a massive, concordant igneous body intruded between preexisting strata
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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
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Laminar flow
|
the movement of water particles in straightline parths that are parallel to the channel. The water particles move downstream without mixing
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Lateral moraine
|
a ridge of till along the sides of a valley glacier composed primarily of debris that fell to the glacier from the valley wall
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Laterite
|
a red, highly leached soil type found in the tropics and rich in oxides of iron and aluminum
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Laurasia
|
the nothern portion of Pangea consisting of North America and Eurasia
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Lava
|
magma that reaches earth's surface
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Lava dome
|
a bulbous mass associated with an old-age volcano, produced when thick lava is slowly squeezed from the vent. Lava domes may act as plugs to deflect subsequent gaseous eruptions
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Lava tube
|
tunnel in hardened lava that acts as a horizontal conduit for lava flowing from a volcanic vent. Lava tubes allow fluid lavas to advance great distances
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Law of superpoistion
|
in any undeformed sequence of sedimentary rocks or surface-deposited igneous materials, each layer is older than the one abovie it and younger than the one below it
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Law of superposition
|
in any undeformed sequence of sedimentary rocks or surface-deposited igneous materials, each layer is olden than the one above it any younger than the one below it
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Leaching
|
the depletion of soluble materials from the upper soil by downward-percolating water
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Light silicate
|
silicate minerals that lack iron and or magnesium. They are generally lighter in color and have lower specific gravities than dark silicates
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Lithification
|
the process, generally by cementation and or compaction, of converting sediments to solid rock
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Lithosphere
|
the rigid outer layer of Earth, including the crust and upper mantle
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Loess
|
deposits of windblown silt, lacking visible layers, generally buff colored, and capable of maintaining a nearly vertical cliff
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Longitudinal Profile
|
a cross section of a stream channel along its descending course from head to the mouth
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|
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Longitudinal Dunes
|
Long ridges of sand oriented paralle to the prevailing windl these dunes form where sand supplies are limited
|
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Longitudinal profile
|
a cross section of a stream channel along its descending course from the head to the mouth
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|
|
Longshore current
|
a nearshore current that flows parallel to the shore
|
|
|
Losing stream
|
stream sthat lose water to the groundwater system by outflow through the streambed
|
|
|
Luster
|
the appearance or quality of light reflected from the surface of a mineral
|
|
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Luster
|
the appearnace or quality of light reflected fromt he surface of a mineral
|
|
|
Mafic
|
because basaltic rocks contain a high percentage of ferromagnesian minerals, they are also called mafic (from magnesium and ferrum, the latin name for iron).
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Magma
|
a body of molten rock found at depth, including any dissolved gases and crystals
|
|
|
Magnetometer
|
a sensitve instrument used to measure the intesity of Earth's magnetic field at various points
|
|
|
Magnitude (earthquake)
|
the total amount of energy released during an earthquake
|
|
|
Manganese nodules
|
a type of hydrogenous sediment scattered on the ocean floor, consisting mainly of manganese and iron, and usually containing small amounts of copper, nickel, and cobalt
|
|
|
Mantle
|
the 2885 kilometer (1789 mile) thick layer of Earth located below the crust
|
|
|
Mantle plume
|
a mass of hotter-than-normal mantle material that ascends toward the suface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core-mantle boundary.
|
|
|
Mass number
|
the sum of the number of neutrons and protons in the nucleus of an atom
|
|
|
Mass wasting
|
the downslope movement of rock, regolith, and soil under the direct influence of gravity
|
|
|
Meander
|
a looplike bend in the course of a stream
|
|
|
Meander Scar
|
a floodplain feature created when an oxbow lake becomes filled with sediment
|
|
|
Mechanical weathering
|
the physical disintegration of rock, resulting in smaller fragments
|
|
|
Medial moraine
|
a ridge of till formed when laterla moraines from two coalescing valley glaciers join
|
|
|
Melt
|
the liquid portion of magma excluding the solid crystals
|
|
|
Mesosphere
|
the part of the mantle that extends from the core-mantle boundary to a depth of 660 kilometers. Also known as the lower mantle.
|
|
|
Mesozoic era
|
a time span on the geologic time scale between the Paleozoic and Cenozoic eras - from about 248 million to 65 million years ago
|
|
|
Metallic Bond
|
a chemical bond present in all metals that may be characterized as an extreme type of electron sharing in which the electrons move freely from atom to atom.
|
|
|
Metamorphic Rock
|
Rock 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
|
|
|
Migmatite
|
a rock exhibiting both igneous and metamorphic rock characteristics. Such rocks may form when lightcolored silicate minerals melt and then crystallize, while the dark silicate mineral remains soid
|
|
|
Mineral
|
a naturally occuring, inorganic crystalline material with a unique chemical struture
|
|
|
Mineral resource
|
all discovered and undiscovered deposits of a useful mineral that can be extracted now or at some time in the future
|
|
|
Modified Mercalli intensity scale
|
a 12-point scale developed to evaluate earthquake intensity based on the amount of damage to various structures
|
|
|
Moho
|
the boundary separating the crust and the mantle, discernible by an increase in seismic velocity
|
|
|
Mohs scale
|
a series of 10 mineral used as a standard in determining hardness
|
|
|
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
|
|
|
Monocline
|
a one-limbed flexure in strata. The strata are usuallly flat lying or very gently dipping on both sides of the monocline
|
|
|
Mouth
|
the point downstream where a river empties into another stream or water body
|
|
|
Mud crack
|
a feature in some sedimentary rocks that forms when wet mud dries out, shrinks, and cracks
|
|
|
Natural Levee
|
the elevated landforms composed of alluvium that parallel some streams and act to confine their waters, except during floodstage
|
|
|
Neap tide
|
the lowest tidal range, occuring near the times of the first and third quarters of the moon
|
|
|
Nebular hypothesis
|
a nodel for the origin of the solar system that assumes a rotating nebula of dust and gases that contracted to produce the Sun and planets
|
|
|
Neutron
|
a subatomic particle found in the nucleus of an atom. The neutron is electrically neutral, with a mass approximately equal to that of a proton
|
|
|
Nonclastic
|
a term for the texdture of sedimentary rocks in which the minerals form a pattern of interlocking crystals
|
|
|
Nonconformity
|
an unconformity in which older metmorphic or intrusive igneous rocks are overlain by younger sedimentary strata
|
|
|
Nonfoiliated
|
metamorphic rocks that do not exhibit foliation
|
|
|
nonmetallic mineral resource
|
mineral resource that is not a fuel or processed for the metals it contains
|
|
|
nonrenewable resource
|
resource that forms or accumulates over such long time spans that it must be considered as fizxed in totaly quantity
|
|
|
normal fault
|
a fault in wich the rock abuve the fault plane has moved down relative to the rock below
|
|
|
normal polarity
|
a magnetic field the same as that which presently exists
|
|
|
nucleus
|
the small, heavy core of an atom that contains its positive charge and most of its mass
|
|
|
nucleus
|
the small, heavy core of an atom that conotains all of its positive charge and most of its mass
|
|
|
nuee ardente
|
incandescent volcanic debris that is buoyed up by hot gases and moves downslope in an avalanche fashion
|
|
|
numerical date
|
date that specifies that actual number of years that have passed since an event occurred
|
|
|
oceanic ridge
|
a continuous mountainous ridge of the floor of all the major ocean basins and varying in width from 500 to 5000 kilometers (300-3000miles). The rifts at the crests of these ridges represent divergent plate boundaries
|
|
|
octet rule
|
atoms combine in order that each may have the electron arrangement of a noble gas; that is the outer energy levell contains eight electrons
|
|
|
oil trap
|
a geologic structure that allows for significant amounts of oil and gas to accumulate
|
|
|
ore
|
usually a useful metallic mineral that can be mined at a profit. The term is also applied to certain nonmetallic minerals such as fluorite and sulfur
|
|
|
original horizontality
|
layers of sediment are generally deposited in a horizontal or nearly horizontal position
|
|
|
Orogenesis
|
the processes that collectively result in the formation of mountain
|
|
|
Outercore
|
a layer beneath the mantle about 2270 km (1410 m) thick that has the properties of a liquid
|
|
|
Outgassing
|
the release of gases dissolved in molten rock
|
|
|
Outlet glacier
|
a tongue of ice normaly flowing rapidly outward from an ice cap or ice sheet, usually through mountainous terrain to the sea
|
|
|
Outwash plain
|
a relatively flat, gently sloping plain consisting of materials deposited by meltwater streams in front of the margin of an ice sheet
|
|
|
Oxbow lake
|
a curved lake produced when a stream cuts off a meander
|
|
|
Oxidation
|
the removal of one of more electrons from an atom or ion. So named because elements commonly combine with oxygen
|
|
|
Pahoehoe
|
a lava flow with a smooth-to-ropy surface
|
|
|
Paleomagnetism
|
the natural remnant magnetism in rock bodies. The permanent magnetization acquired by rock that can be used to determine the location of the magnetic poles and thae latitude of the rock at the time it became magnetized
|
|
|
Paleontology
|
the systematic study of fossils and the history of life on earth
|
|
|
Paleozoic era
|
a time span of the geologic time scale between the Precambrian and Mesozoic eras-from about 540 million to 248 million years ago
|
|
|
Pangaea
|
the proposed supercontinent that 200 million years ago began to break apart and form the present landmasses
|
|
|
Parabolic dune
|
a sand dune similar in shape to a barchan dune expect that its tips point into the wind. These dunes often form along coasts that have strong onshore winds, abundant sand, and vegetation that partly covers the sand
|
|
|
Paradigm
|
theory that is held with a very high degree of confidence and is comprehesive in scope
|
|
|
Parastic cone
|
a volcanic cone that forms on the flank of a larger volcano
|
|
|
Parent material
|
the material upon which a soil develops
|
|
|
Parent rock
|
the rock from which a metamorphic rock formed
|
|
|
Partial melting
|
the process by which most igneous rocks melt. Because individual minerals have different melting points, most igneous rocks melth over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occured, a melt with a higher silica content results
|
|
|
Passive continental margin
|
a margin that consists of a continental shlef, continental slope, and continental rise. The are NOT associated with plate boundaries and therefore experience little volcanism and few earthquake
|
|
|
Pedalfer
|
soil of humid regions characterized by the accumulation of iron oxides and aluminum-rich clays in the B horizon
|
|
|
Pedocal
|
soil associated with drier regions and characterized by an accumulation of calcium carbonate in the upper horizons
|
|
|
Pegmatite
|
a very coarse-grained igneous rock (typically granite) commonly found as dike associated with a large mass of plutonic rock that has smaller crystals. Crystalization in water-rich environment is believed to be responsible for the very large crystals
|
|
|
Pegmatitic Texture
|
a texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in dimater
|
|
|
Peneplain
|
in the idealized cycle of landscape evolution in a humid region, an undulating plain near base level associated with old age
|
|
|
Perched water table
|
a localized zone of saturation above the main water table created by an impermeable layer (aquitard)
|
|
|
Peridotite
|
an igneous rock of ultramafic compoistion through to be abundant in the upper mantle
|
|
|
Period
|
a basic unit of the geologic calendar that is a subdivision of an era. Periods may be divided into smaller units called epochs
|
|
|
Permafrost
|
any permanently frozen subsoil. Usually found in the subartic and artic regions
|
|
|
Permeability
|
a measure of a material's ability to transmit water
|
|
|
Phaneritic texture
|
an igneous rock texture in which the crystals are roughly equal in size and large enough so that individual mineral scan be identified with the unaided eye
|
|
|
Phanerozoic Eon
|
that part of geologic time represented by rocks containing abundant fossil evidence. The eon extending from the end of the Proterozoic eon (about 540 mmillion years ago) to the present)
|
|
|
Phenocryst
|
conspicuously large crystals in a porphyry that are imbedded in a matrix of finergrained crystals (the ground mass)
|
|
|
Physical Geology
|
a major division of geology that examines the materials of Earth and seeks to understand the processe and forces acting upon Earth's surface from below
|
|
|
Piedmont Glacier
|
a glacier that forms when one or more valley glaciers emerge from the confining wallas of mountain valles and spread out to create a broad sheet in the lowlands at the base of the mountains
|
|
|
Pillow lava
|
basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows
|
|
|
Pipe
|
a vertical conduit through which magmatic materials have passed
|
|
|
Placer
|
deposit formed when heavy minerals are mechanically concentrated by currents, most commonly streams and waves. Placers are sources of gold, tin, platinum, diamonds, and other valuable minerals
|
|
|
Plastic deformation
|
permanent deformation that results in a change in size and shape through folding or flowing
|
|
|
Plastic flow
|
a type of glacial movement that occurs within the glacier, below a depth of approximately 50 meters, in which the ice is not fractured
|
|
|
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 Earth's outer shell consists of individual plates, which interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself
|
|
|
Playa
|
the flat central area of an undrianed desert basin
|
|
|
Playa lake
|
a temporary lake in a playa
|
|
|
Pleistocene epoch
|
an epoch of the Quaternary period beginning about 1.6 million years ago and ending about 10,00 years ago. Best known as a time of extensive continental ice sheets
|
|
|
Plucking
|
the process by which pieces of bedrock are lifted out of place by a glacier
|
|
|
pluton
|
a structure that results from the emplacement and crystallization fo magma beneath Earth's surface
|
|
|
Pluvial lake
|
a lake formed during a period of increased rainfuall. For example, this occured in many nonglaciated areas during periods of ice advance elsewhere
|
|
|
Point bar
|
a crescent-shaped accumulation of sand and gravel deposited on the inside of a meander
|
|
|
Polar wandering hypothesis
|
as the result of paleomagnetic studies in the 1950s, researchers proposed that either the magnetic poles migrated greatly through time or te continents had gradually shifted their positions
|
|
|
Polymorphs
|
two or more mineral shaving the smae chemical composition but different crystalline structures. Exemplfied by the diamond and graphite forms of carbon
|
|
|
Porosity
|
the volume of open spaces in rock or soil
|
|
|
Porphyritic texture
|
a texture of metamorphic rocks in which particularily large grains (porphyroblasts) are surrounded by a fine-grained matric of other minerals
|
|
|
Porphyritic texture
|
an igneous rock texture characerized by two distinctly different crystal sizs. The large crystals are called phenocrsysa, and the matirc of smaller crystals is termed the groundmass
|
|
|
porphroblastic texture
|
a texture of metamorphic rocks in whic hparticularly large grains (porphyroblats) are surrounded by a fine-grained matricx of other minerals)
|
|
|
Porphyry
|
an igneous rock with a porphyritict texture
|
|
|
Pothole
|
a depression formed in a steram channel by the abrasive action of the water's sediment load
|
|
|
Precambrian
|
al geologic time prior to the Paleozoic era
|
|
|
Principle of fossil succession
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fossil organisms succed one another in a definite and determinable order, and any time period can be recognized by its fossil content
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Principle of original horizontality
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ayers of sediment are generally deposited in a horizontal or nearly horizontal position
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Proterozoic eon
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the eon following the ARchean and preceding the Phanerozoixc eon. It exdtends between 2.5 billion and 540 million years ago
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Proton
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a positively charged subatomic particle found in the nucleus of an atom
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P wave
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the fastest earthquake wave; travels by compression and expansion of the medium
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Pyroclastic flow
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a highly heated mixture, largely of ash and pumic fragments, traveling down the flanks of a volcano or along the surface of the ground
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Pyroclastic material
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the volcanic rock ejected during an eruption. Pyroclastics include ash, bombs, and blocks
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Pyroclastic texture
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as igneous rock texture resultig from the consolidation of individual rock fragments that are ejected during a violent eruption
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Radial drainage
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a system of streams running in all directions away from a central elevated structure, such as a volcano
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Radioactivity
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the spontaneuos decay of certain unstable atomic nuclei
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Radiocarbon (carbon-14)
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the radioactive isotope of carbon produced continuously in the atmosphere and used in dating events as far back as 75,000 years
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Radiometric dating
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the procedure of calculating the absolute ages of rocks and minerals containing certain radioactive isotopes
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Rainshadow desert
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a dry areea on the lee side of a mountain range. Many middle latitude deserts are of this type
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Rapidsq
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a part of a stream channel in which the water suddenly beings flowing more swiftly and turbulently because of an abrupt steepening of the gradient
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Recessional moraine
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an end moraine formed as the ice front stagnated during glacial retreat
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Rectangular pattern
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a drainage pattern that develops on jointed or fractured bedrock and is characterized by numerous right-angle bends
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Refraction
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a change in direction of waves as they enter shallow water. The portion of the wave in shallow water is slowed, which causes the wave to bend and align with the underwater contours
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Regional metamorphism
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metamorphism associated with large-scale mountain building
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Regolith
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the layer of rock and mineral fragments that nearly everywhere covers Earth's land surface
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Relative dating
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rocks are placed in their proper sequence or ordeer. Only the chronolofical order of events is determined
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Renewable resource
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a resource that is virtually inexhausitble or that can be replenished over relatively short time spans
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reserve
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already identified deposits from which minerals can be extracted profitably
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reservoir rock
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the porous, permeable portion of an oil trap that yields oil and gas
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Renewable resource
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a resource that is virtually inexhaustible or that can be replenished over relatively over short time spans
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Reserve
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already identified deposits from which minerals can be extracted profitably
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Reservoir Rock
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the porous, permeable portion of an oil trap that yields oil and gas
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Residual soil
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osoil developed directly from the weathering of the bedrock below
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Reverse fault
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a fault in which the material above the fault plane moves p in relation to the material below
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Reverse polarity
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a magnetic field opposite to that which present exists
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Richter scale
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a scale of earthquake magnitude based on the motion of a seismohraph
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Ridge push
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a mechanism that may contriuvte to plate motion. It involves the oceanic litosphere sliding down the oceanic ridge under the pull of gravity
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Rift
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a region of Earth's crust along which divergence (speratation) is taking place
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Ripple marks
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small waves of sand that develop on the surface of a sediment layer by the action of moving water or air
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Roche moutonnee
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an asymeetrical know of bedrock formed when glacial abrasion smoothes the gentle slope facing the advancing ice sheets and plucking steepens the opposite side as the ice overrides the knob
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Rock
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a consolidated mixture of minerals
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Rock avalanche
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the very rapid downslopemovement of rock and debris. These rapid movements may be aided by a layer of air tapped beneat the debris, and they have been known to reach speeds in excess of 200 kilometers per hour
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Rock cleavage
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the tendency of rock to split along parallel, closely spaced surfaces. These surfaces are often highly inclined to the bedding planes in the rock
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Rock cycle
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a model that illustrates the origin of the three basic rock types and the interrelatedness of Earth's materials and processes
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Rock flour
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ground-up rock produced by the grinding effect of a glacier
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Rockslide
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the rapid slide of a mass of rock downslope along planes of weaknesss
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Runoff
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water that flows over the land rather than infiltrating into the ground
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Saltation
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transportation of sediment through a series of leaps or bounces
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salt flat
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a white crust on the ground produced when water evaporates and leaves its dissolgved naterials behind
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Schistosity
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a type of foliatio characteristic of coarser grained metamorphic r ocks. Suc h rocks have a parallel arrangement of platy minerals such as the micas
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Scoria
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hardened lava that has retained the vesicles produced by esaping gases
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Sea arch
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an arch formed by a wave erosion when caves on opposite sides of a headland unite
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seafloor spreadng
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the hypothesis first proposed in 1960s by Harry Hess that suggested that new oceanic crust is produced at the crests of mid-ocean ridges, which are the sites of divergence
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Seamount
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an isolated volcanic peak that rises atleast 100 meters (330feet) above the deep-ocean floor
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Sea stack
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an isolated mass of rock standing just offshore, produced by wave erosion of a headland
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Seawall
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a barrier constructed to prevent waves from reaching the area behind the wall. Its purpose is to dfend property from the force of breaking waves
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Secondary enrichment
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the concentration of inor amounts of metals that are scattered through unwearthered rocks into economically valuable concentrations by wearering processes
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Secondary S wave
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a seismic wave that involves oscillation perpendicular to the direction of propagation
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Sediment
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unconsolidated particles created by the waerering and erosion of rock, by chemical precipitations from solution in water, or from the secreatios of organisms , and transported bt waterm wind, or glaciers
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Sedimentary rock
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rock formed from the weathered products of preexisteing rocks that have been transported, depoisted, and lithified
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Seiche
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the rhythmic sloshing of water in lkaes, reservoirs, and toher smaller enclosed basinbs, Some seiches are initiated by earthquake activity
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Seismic sea wave
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a rapidly moving ocean wave genenreated by earthquake activity an capable of inflicting heavy damage iin coastal regions
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Seismogram
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the record made by a seismograph
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Seismograph
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an instrument that records earthquake waves
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Seismology
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the study of earthquakes and seismic waves
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Settling velocity
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the speed at which a particle flals through a still fluid. The size, shape, and specific gravity of particles influence settling velocity
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Shadow zone
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the zone between 105 and 140 degrees distance from an earthquake epicenter that direct waves do not penetrate becaues of refraction by Earth's core
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Shallow-focus earthquake
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an earthquake focus at a depth of less than 60km
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Shear
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stress that caues two adjacent parts of a budy to side past one another
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Sheet flow
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runoff moving in unconfined thin sheets
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Shelf break
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the point at which a rapid steepening of the gradient occurs, marking the outer edge of the continental shelf and the beginning of the continental slope
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Shield
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a large, relatively flat expanse of ancient metamorphic rock within the stagble continental interior
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Sheid volcano
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a broad, gently sloping volcano uilt from fluid basaltic lavas
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Silcate
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any one of numerous minerals that have the silicon-oxygen tetrahedron as their bvasic structure
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Silicon-oxygen tetrahedron
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a structure composed of four oxygen atoms surrounding a silicon atom that constitutes the basic building block of silicate mienrals
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sill
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a tabular igneous body that was intruded parallel to the basic building block of silicate minerals
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sinkhole
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a depression produced in a region where soluble rock has been removed by groundwater
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slab-pull
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a mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and "pulls" the trainling lithosphere along
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slaty cleavage
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the type of foliation characteristics of slates in which there is a parallel arrangement of fine-grained metamorphic minerals
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slide
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a movement common to mass-wasting processes in whcih the material moving downslope remains fairly coherent and moves along a well-defined surface
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slip face
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the steep, leeward sufrace of a sand dune that maintans a slope of about 34 degrees
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slump
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the downward slipping of a mass of rock or unconsolidated material moving as a unit along a curved surface
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snowfield
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an area where snow persists year-round
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snowline
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lower limit of perennial snow
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soil
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a combination of mineral and organic matter, water, and airl that portion of the regolith that supports plant growth
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Soil horizon
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a layer of soil that has identifiable characteristics produced by chemical weathering and other soilforming processes
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Soil profile
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a vertical section through a soil showing its succesion of horizons and the underliying parent material
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solifluction
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slow, downslope flow of water-saturated materials common to permafrost areas
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Solum
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the O, A, and B horizons in a soil profile. Living roots and other plants and animal life are largely confined to this zone
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Solution
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the change of matter from the solid or gaseous state into the liquid state by its combination with liquid
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Sorting
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the degree of similarity in particle size in sediment or sedimentary rock
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specific gravity
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the ratio of a s substances weight to the weight of an equal volume of water
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Speleothem
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a collective term for the dripstone features found in caverns
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Spheroidal weathering
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any weathering process that tends to produce a spherical shape from an initially blocky shpae
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Spit
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an elongated ridge of sand that projects fronm the land into the mouth of an adjacent bad
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Spring
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a flow of groundwater that emerges naturally at the ground surface
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Spring tide
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the highest tidal range;p occurs near the times of the new and full moons
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stalactite
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the icicle-like structure that hangs from the ceiling of a cavern
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stalagmite
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the columnlike form that grows upward from the floor of a cavern
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star dune
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isolate dhill of sand that exhibits a complex form and develops where wind conditions are variable
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Steppe
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one of the two types of dry climate. A marginal and more humid variant of the desert that separates the desert from bordering humid climate
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Stock
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a pluton similar to but smaller than a batholith
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Strata
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parallel layers of sedimentary rock
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Stratified drift
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sediments deposited by glacial meltwater
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Streak
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the color of a mineral in powdered form
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Stream
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a general term to denote the flow of water within any natural channel. Thus, a small creek and a large river are both streams
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Stress
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the force per unit area acting on any surface within a solid
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Striation
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the multitude of fine parallel lines found on some cleavage faces of plagioclase feldspars but not present of orthoclase feldspar
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Striations - glacial
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scratches or grooves in a bedrock surface caused by the grinding action of a glacier and its load of sediment
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Strike
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the compass direction of the line of intersection created by a dipping bed of fault and a horizontal surface. Strike is always perpendicular to the direction of dip
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Strike-slip fault
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a fault along which the movement is horizontal
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Strike
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the compass direction of the liner or intersection created by a dipping bed of fault and a horizontal surface. Strike is ALWAYS perpedicular to the directio of dip
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Strike-slip fault
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afault along which the movement is horizontal
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Stromatolite
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structures that are deposited by algae and that consist of layered mounds or colums of calcium carbonate
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subduction
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the process oft hrusting oceanic lithosphere into the mantle along a convergent zone
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subduction zeon
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a long, anrrow zone where one lithospheric plate descends beneath another
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Submarine canyon
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a seaward extension of a valley that was cut on the continental shelf during a time when sea level was lower, or a canyon carved into the outer continental shlef, slop, and riseby turbidity currents
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Submergent coast
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a coast whose form is largely the result of the partial drowing of a former land surface either due to a rise of sea level or subsidence of the crust, or both
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Subsoil
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a term applied to the B horizon of a soil profile
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law of superposition
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in any undeformed sequence of sedimentary rocks, each bed is older than the one abouve and youner thanthe one below it
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Surf
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a collective term for breakers; also the wave activity in the area between the shoreline and the outer limit of breakers
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Surface soil
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the upper portion of a soil profile consisting of the O and A horizons
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Surface waves
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seismic waves that travel along the outer layers of earth
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Surge
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a period of rapid glacial advance; surges are typically sporadic and short-lived
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Suspended load
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the fine sediment carried within the body of flowing water orair
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Swave
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an earthquake wave, slower than a P wave, that travels only in solids
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Swells
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wind-generated waves that have moved into an area of weaker winds or calm
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Syncline
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a linear downfold in sedimentary strata; the opposite of anitcline
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System
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a group of initeracting or interdependent parts that form a complex whole
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Tabular
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describing a feature such as igeneous pluton having two dimensions that are much longer than the thrid
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Talus
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an accumulation of rock debris at the base of a cliff
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Tarn
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a small lake in a cirque
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Tectonics
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the study of the large--scale processes that collectively deform Earth's crust
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Temporary (local) base level
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the level of a lake, resistant rock layer, or any other bvase level that stands above sea level
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Terminal moraine
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the end moraine marking the farthest advance of a glacier
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Terrace
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a flat, benchlike structure produced by a stream that was left elevated as the stream cut downward
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Terrane
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a crustal block bounded by faults whose geologic history is distinct from the histories of adjoining crustal blocks
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Terrigenous sediment
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seafloor sediment derived from terrestiral weathering and erosion
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Texture
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the size, shape, and distribution of the particles that collectively constitute a rock
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Theory
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a well-tested and widely accepted view that explain certain observable facts
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Theory
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a well-tested and widley accpeted view that explains certain observable facts
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Thermal metamorphism
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same as contact metamorphism
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Thrust fault
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a low-angle reverse fault
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Tide
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periodic change in the elecation of the ocean's surface
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Till
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unsorted sediment deposited directly by a glacier
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Tillite
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a rock formed when glacial till is lithified
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Tombolo
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a ridge of sand that connects an island to the mainland or the another island
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Topset bed
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as essentially horizontal sedimentary layer deposited on top of a delta during floodstage
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Transform fault
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a major strike-slip fault that cuts through the lithosphere and accommodates motion between two plates
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Transform fault boundary
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a boundary in which tow plates slide past one another without creating or destroying lithosphere
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Transpiration
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the release of water vapor to the atmosphere by plants
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Transported soil
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soils that form on uncosolidated deposits
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Trancerse dunes
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a series of long ridges orientate at right angles to the prevailing windl these dunes form where vegetation is sparse and sand is very plentiful
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Travertine
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a form of limestone (CaCO3) that is deposited by hot sprinfs or as a case deposit
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Trellis drainage
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a system of streams in which nearly parallel tributaries occupy valleys cut in folded strata
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Trench
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an elongate depression in the seafloor produced y bending of oeanic crust during subduction
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Tsumani
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the japanese word for a seismic sea wave
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Turbidite
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turbidity current deposit characeterized by graded bedding
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Turbidity Current
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a downslope movement of dense, sediment-laden water created when sand and mud on he continental shelf and slope are dislodged and thrown into suspension
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Turbulent Flow
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the movement of water in an erratic fashion often characterized by swirling, whirlpool-like eddies. Most streamflow is of this type
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Ultimate base level
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sea level; the lowest level to which stream erosion could lower the land
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Ultramafic
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composition catergory for igneous roks made up almost entirely or ferromagnesion mineral (olivine and pyroxene)
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Unconformity
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a surface that represents a break in the rock recordl caused by erosion or nodeposition
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Uniformitarianism
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the concept that the processes that havec shpaed Earth in the geologic past are essentially the same as those operating today
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Valence Electron
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the electrons involved in the bonding process; the electrons occupying th ehighest principal energy level of an atom
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Valley glacier
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a glacier confined to a mountain valley, which in most instances had previously been a stream valley
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Valley train
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a relatively narrow body of stratified drift deposited on a valley floor by melthwater streams that issue from the terminus of a valley glacier
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Vein deposit
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a mienral filling a fracture or fault in a host rock. Such deposits have a sheetlike, or tabular form
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Ventifact
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a cobble or pebble polished and shpaed by the sandblasting effect of wind
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Wesicles
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spherical or elongated epenings on the outer portion of a lava flow that were created by escaping gas
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Vesicular texture
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a term applied to aphanitic igenous rocks that contain many small cavities, called vesicles
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Viscosity
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a measure of a fluid's resistance to flow
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Volatiles
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gaseous components of magma dissolved in the melt. Volatiles will readily vaporize( forma gas) at surface pressures
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Volcanic
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pertaining to the activities, structures, or rock types of a volcano
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Volcanic island arc
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a chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another
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Volcanic bond
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a streamlined pyroclastic fragment ejected from a volcano while the fragment is still molten
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Volcanic neck
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an isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano
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Volcano
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a mountain formed from lava and or pyroclastics
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Wash
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a desert stream course that is typically dry except for brief periods immediately following rainfall
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Water gap
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a pass through a ridge or mountain in which a stream flows
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Water table
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the upper level of the saturated zone of ground-water
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Wave-cut cliff
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a seaward-facing cliff along a steep shoreline formed by wave erosion at its bse and by mass wasting
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wave-cut platform
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a bench or shelf along a shore at sea level, cut by wave erosion
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Wave height
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the vertical distance between the trough and crest of a wave
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Wave length
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the horizontal distance separating successive crests or troughs
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Wave of oscillation
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a water wave in which the wave form advances as the water particles move in circular orbits
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Wave translation
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the turbulent advance of water created by breaking waves
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Weathering
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the disintegration and decomposition of rock at or near the surface of the Earth
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Wave of translation
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the turbulent advance of water created by breaking waves
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Wave period
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the time interval between the passage of successie creats at a stationary point
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Weathering
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the disintegration and decomoposition of rock at or near the surface of the earth
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Welded tuff
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a pyroclastic deposit composed of particles fused together by the combination of heat still contained in the deposit after it has come to rest and by the weight of overlying material
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Well
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an opening bored into the zone of saturation
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Wind gap
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an abandonend water gap,. These gorges typically result from stream piracy
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Xenolith
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an inclusion of unmelted country rock in an igneous pluton
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Xerophyte
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a plant highly tolerant of drought
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Yazoo tributary
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a tributary that flows parallel to the main stream because a natural levee is present
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Zone of accumulation
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the part of a glacier characterized by snow accumulation and ice formation. The outer limit of this zone is the snowline
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Zone of aeration
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area above the water table where openings in soil, sediment, and rock are not saturated but are filled mainly with air
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Zone of fracture
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the upper portion of a glacier consisting of brittle ice
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Zone of saturation
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zone where all open spaces in sediment and rock are completely filld with water
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