Glossary of Geology 101 2

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A type of lava flow that has a jagged, blocky surface.
A general term for the loss of ice and snow from a glacier
The grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, or ice.
Abyssal plain
Very level area of the deep-ocean floor, usually lying at the foot of the continental rise
Accretionary Wedge
A large wedge-shaped mass of sediment that accumulates in subduction zones. Here sediment is scraped from the subducting oceanic plate and accreted to the overriding crustal bloc.
Active continental margin
usually narrow and consisting of highly deformed sediments. They occur where oceanic lithoshpere is being subducted benearth the margin of a continent
Active layer
The zone above the permafrost that thaws in summer and refreezes in winter.
A smaller earthquake that follows the main earthquake
Alluvial Fan
a fan-shaped deposit of sediment formed when a stream's slope is abruptly reduced
unconsolidated sediment deposited by a stream
Igneous rocks having a mineral makeup between that of grante and basalt, after the common volcanic rock andesite
Angle of repose
the steepest angel at which loose material remains stationary without sliding downslope
Angular unconformity
An unconformity in which the older strata dip at an angle different from that of the younger beds
a hard, metamorphic form of coal that burns clean and hot.
a fold in sedimentary strata that resembles an arch
Aphanitic Texture
a texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished with the unaided eye.
rock or sediment through which groundwater moves easily
an impermeable bed that hinders or prevents groundwater movement
Archean eon
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.
A narrow, knifelike ridge separating two adjacent glaciated valleys.
A feldspar-righ sandstone
Artesian Well
a well in which the water rises above the level where it was initially encountered.
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
The gasous portion of a plante; the planet's enevelope of air. One of the traditional subdivisions of Earth's physical environment
A continuous or broken ring or coral reef surrounding a central lagoon
the smallest particle that exists as an element
Atomic mass unit
A mass unit equal to exactly one-twelfth the mass of a carbon-12 atom
Atomic number
the number of protons in the nucleus of an atom
Atomic Weight
the average of the atomic masses of isotopes in a give element
a zone or halo of contact metamorphism found in the host rock surrounding an igneous intrusion
Back swamp
a poorly drained area on a floodplain, resulting when natural levees are present
common term for sand and gravel deposits in a stream channel
Barchan dune
a solitary sand dune shaped like a crescent with its tips pointed downwind
Barchanoid dunes
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
Barrier island
a low, elongated ridge of sand that parallels the coast
Basal slip
a mechanism of glacial movement in which the ice mass slides over the surface below
an aphanitic igneous rock of mafic composition
term used to describe igneous rocks that contain abundeant dark (ferromagnesian) minerals and about 50 percent silica
Base level
the level below which a stream cannot erode
a circular downfolded structure
a large mass of igneous rock that formed when magma was emplaced at depth, crystallized, and was subsequently exposed by erosion
Baymouth Bar
a sandbar that completely crosses a bay, sealing it off from the main body of water
Beack drift
the transport of sediment in a zigzag pattern along a becak. It is caused by the uprush of water form obliquely breaking waves
Beach nourishment
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.
Bedding plane
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.
Bed load
sediment rolled along the bottom of a stream by moving water, or particles robed along the ground surface by wind
Belt of soil moisture
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.
describing a type of chemical sediment that form swhen material dissolved is water is precipatead by water-dwelling organisms. Shells are common examples
Biogenous sediment
seafloor sediments consisting of material or marine-organic origin
Bituminous coal
the most common form of coal, ofter called soft, black coal
blowout (deflation hollow)
a depression excavated by wind in easily eroded materials
body wave
a seismic wave that travels through Earth's interior
bottomset bed
alayer of fine sediment deposited beyond the advancing edge of a delta and then buried by continuous delta growth
Bowen's reaction series
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
Braided stream
a stream consisting of numerous intertwining channels
a structure protecting a nearshore area from breaking wave
a sedimentary rock composed of angular fragments that were lithifiedq
Brittle deformation
deformation that in volves the fracturing of rock Associated with rocks near the surface
Burial metamorphism
low-grade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata
a large depression typically caused by collapse of the summit area of a volcano following a violent eruption
a hard layer, rich in calcium carbonate, that forms beneath the B horizon in soils of arid regions
wastage of a glacier that occurs when large pieces of ice break off into water
the total amount of sediment a stream is able to transport
Capillary fringe
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.
Cap rock
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.
the concept that Earth was shaped by catastrophic events or a short -term nature
a naturally formed underground chamber or serioes of chambers most commonly prodeuced by solution activity in limestone
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
Cenozoic era
a time span on the geologic time scale beginning about 65 million years ago following the Mesozoic era
Chemical sedimentary rock
sedimentary rock consisting of material that was precipitated from water by either inorganie or organic means
Chemical weathering
the processes by whcih the internal structure of a mineral is altered by the removal and/or addition of elements
Cinder cone
a rather small volcano built primarily of pyroclastics ejected from a single vent
an amphitheater-shpaed basin at the head of a glaciated valley produced by frost wedging and plucking
a sedimentary rock texture consisting of broken fragments of preexisting rock
the tendency of a mineral to break along planes of weak bonding
a pass between mountain valleys where the headwalls of two cirques intersect
a phenomenon of light by which otherwise identical objects may be differentiated
a feature found in cabes that is formed when a stalactite and stalagmite join
Columnar joints
a pattern of crack sthat forms during cooling of molten rock to generate columns
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.
a measure of the largest particle a stream can transport; a factor dependent on velocity
Composite cone
a volcano composed of both lava flows and proclastic material
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
a term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock
a piplike opening through which magma moves toward earth's surface. It terminates at a surface opening called a vent.
Cone of depression
a cone-shaped depression immediately surrounding a well
Confortable layers
rock layers that were deposited with-out interruption
a sedimentary rock consisting of rounded, gravel-size particles
contact metamorphism
changes in rock cause by the heat of a nearby magma body
Continental drift
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.
Continental rise
the gently sloping surface at the vase of the continental slope
continental shelf
the gently sloping submerged portion of the continental margin, extending from the shoreline to the continental slope
Continental slope
the steep gradient that leads to the deep ocean floor and marks the seaward edge of the continental shelf
Continental volcanic arc
mountains formed in part byt igneous activity associated with the subduction of oceanic lithoshpere beneath a continent. Examples include the Andes and the Cascades.
Convergent plate boundary
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
located beneath the mantle, it is Earth's innermost layer. The core is diveided into an outer core and an inner core.
establishing the equialence of rocks of similar age in different areas
the depression at the summit of a volcano or that which is produced by a meterorite impcat
the slow downhill moveent of soil and regolith
a deep crack in the brittle surface of a glacier
structure inwhich relatively thin layers are inclined at an angle to the main bedding. Formed by currendts of wind or water.
a principle of relative dating. A rock or fault is younbger than any rock (or fault) through which it cuts
the very thing, outermost layer of earth
an orderly arrangement of atoms
Crystal form
the external appearance of a mineral as determined by its internal arrangement of atoms
the formation and growth of a crystalline solid from a liquid or gas
Curie point
the temperature above which a material loses its magnetization
Cut bank
the area of active erosion on the outside of a meander
a short channel segment created when a river erodes through the narrow neck of land between meanders
Dark Silicate
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
Daughter product
an isotope resulting from radioactive decay
Debris flow
a relatively rapid type of mass wating that involves a flow of soil and regolith containing a large amount of water. Also called mudflows
Decompression melthing
melting that occurs as rock ascends due to a drop in confining pressure.
Deep-focus earthquake
an earthquake focus at a depth of more than 300 kilometers
Deep-ocean basin
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.
the lifting and removal of loose material by wind
general term for the processes of folding, faulthing, shearing, compression, or extension of rocks as the result of various natural forces
an accumultaion of sediment formed where a stream enters a lake of ocean
Dendritic pattern
a stream system that resembles the pattern of a branching tree
the weight per unit volume of a particular material
one of the two types of dry climate; the of the dry climates
Desert pavement
a layer of coarse pebbles and gravel created when wind removes the finer material
Detachment fault
a low-angle fault that represents a major boundary between unfaultted rocks below that exhibit brittle deformation via faulting
Detrital sedimentary rocks
rocks that form from the accumulation of materials that originate and are transported as solid particles derived from both mechanicla and chemical weathering
a collective term for all the chemical, physical, and biological changes that take place after sediments are deposited and during and after lithifaction
a tabular-shaped intrusive igneous feature that cuts through the surrounding rock
the angle at which a rock layer is inclined from the horizontal. The direction of dip is at a right angle to the strike
Dip-slip fault
a fault in which the movement is parallel to the dip of the fault
the quantity of water in a stream that passes a given point in a given period of time
a type of unconformity in which the beds above and below are parallel
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.
a term used to describe plutons that cut across existing rock structures, such as bedding planes
Disseminated deposit
any economic mineral deposit in which the desired mineral occurs as scattered particles in the rock but in sufficient quantity to make the deposit an ore
Dissolved load
the portion of a stream's load carried in solution
a section of a stream that leaves the main flow
Diurnal tide
a tide characterized by a single high and low water height each tidal day
Divergent plate boundary
a boundary in which two plates move apart, resulting in upwelling of materiial from mantle to create a new sea floor
an imaginary line that seperates the drainage of two streams; often found along a ridge
a roughly cicular, upfolded structure
drainage basin
the land area that contributes water to a stream
the difference in height between the bottom of a cone of depression and the original height of the water table
a streamlined asymmetrical hill composed of glacial till. The steep side of the hill faces the direction from which the ice advanced
dry climate
a climate in which the yearly precipitation is less than the potential loss of water by evaporation
Ductile deformation
a type of solid-state flow that produces a change in the size and shape of a rock body without fracturing. Occurs at depths where temperatures and confininf pressures are high
a hill or ridge of wind-deposited sand
the downslope movement of water-saturated clay-rich sediment. Most characteristic of humid regions.
vibration of earth produced by the rapid release of energy
Echo sounder
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
Elastic deformation
nonpermanent deformation in which rock returns to its original shape when the stress is released
elastic rebound
the sudden release of stored strain in rocks that results in movement along fault
a negatively charged subatomic particle that has negligible mass and is found outside the atom's nucleus
a substance that cannot be decomposed into simpler substances by oridnary chemical or physical means
Emergent Coast
a coast where land formerly below the sea level has been exposed either by crustal uplift or a drop in sea level of both
End moraine
a ridge of till marking a former position of the front of the glacier
Energy-level shell
the region occupied by electrons with a specific energy level
the largest time unit of the geologic time scale, next in order of magnitude above is...era
the location of Earth's surface that lies directly above the focus of an earthquake
a unit of the geological time scale that is a subdivision of a period
a major division on the geologic time scale; eras are divided into shorter units called periods
the incorporation and transportation of material by a mobile agent, such as water, wind, or ice
Eruption column
buoyant plumes of host ash-laden gases that can extend thousands of meters into the atmosphere
sinuous ridge composed largely of sand gravel deposited by a stream flowing in a tunnel beneath a glacier near its terminus
a partially enclosed coastal water body that is conneted to the ocean. Salinity here is measurably reduced by the freshwater flows of rivers
a sedimentar rock formed of material deposited from solution by evaporation of water
the combined effect of evaporation and transpiration
Exfoliation Dome
large, dome-shaped structure, usually composed of granite, formed by sheeting
Exotic stream
a permanent stream that traverses a desert and has its source in well-watered ares outside the desert
External process
process such as weathering, mass wating, or erosion that is powered by the Sun and transforms solid rock into sediment
igneous activity that occurs at Earth's surface
a type of movement common to mass0wasting processes that refers to the free falling of detached individual pieces of any size
a break in a rock mass along which movement has occured
Fault-block mountain
a mountain formed by the displacement of rock along fault
Fault creep
slow, gradula displacement along a fault that occurs relatively smoothly and with little noticeable seismic activity
Fault scarp
a cliff created by movement along a fault. It represents the exposed surface of the fault prior to modification by weathering and erosion
a term derived from feldspar and silica (quartz). It is a term used to describe granitic igneous rocks
the distance that the wind has traveled across the open water
a steep-sided inlet of the sea formed when a glacial trough was partially submerged
a crack in rock along which there is a distinct separation
Fissure eruption
an eruption in which lava is extruded from narrow fractures or cracks in the crust
the overflow of a stream channgel that occurs when discharge exceeds the channel's capactiy. The most common and destructive geologic hazard
Flood basalts
flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of meters
the flat, low-lying prtion of a stream valley subject to periodic inundation
a type of movement common to mass-wasting processes in which water-saturated material moves downslope as a viscous fluid
the absorption of ultraviolet light, which is reemited as visible light
a best layer or series of layers that were originally horizontal and subsequently deformed
a texture of metamorphic rocks that gives the rock a layered appearance
a term for a linear arrangement of textural features often exhibited by metamorphic rocks
foreset bed
an inclined bed deposited along the front of a delta
small earthquakes that often precede a major earthquake
the remains or traces of organisms preserved from the geologic past
fossil fuel
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
Fossil succession
fossil organisms succeed one another in a definite and determinable order, and at any time period can be recognized by its fossil content
Fractional crystalization
the process that seperates magma into components having varieds compositions and melting points
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
Fracture (rock)
any break or rupture in rock along which no appreciable movement has taken place
Frost wedging
the mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices
a vent in a volcanic area from which fumes or gases escape
Gaining stream
streams that gain water from the inflow of groundwater through the streambed
the science the examines Earth, its form and composition, and the changes it has undergone and is undergoing
Geothermal Energy
natural steam used fro power generation
Geothermal gradient
the gradual increase in temperature with depth in the crust. The average is 30degrees C per kilometer in the upper crust
a fountain of hot water ejected periodically from the ground
Glacial Budget
the balance, or lack of balance, between accumulation oat the upper end of a glacier, and loss at the other end
Glacial drift
an all-embracing term for sediments of glacial origin, no matter how, where, or in what shape they were deposited
Glacial erratic
an ice-transported boulder that was not derived from the bedrock near its present site
Glacial striations
scratches and grooves on bedrock cuased by glacial abrasion
Glacial trough
a mountain valley that has been widened, deepened, and straightened by a 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.
Glass (volcanic)
natural glass produced when molten lava cools too rapidly to permit crystallization. Volcanic glass is a solid composed of unordered atoms
Glassy texture
a term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals
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
the southern portion of Pangaea consisting of South America, Africa, Australia, India, and Antartica
a valley formed by the downward displacement of a fault-bounded block
Graded bed
a sediment layer characterized by a decrease in sediment size from bottom to top
Graded stream
a stream that has the correct channel characterisitcs to maintain the exact velocity required to transport the material supplied to it
igneous rocks composed mainly of light coloered silicates (quartz and feldspar) are said to have this composition
the slop of a stream; generally measured in feet per mile
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
a short wall built at a right angle to the seashore to trap moving sand
the matrix of smaller crystlas within an igneous rock that has porphyritic texture
Ground moraine
an undulating layer of till deposited as the ice front retreats
water in the zone of saturation
a submerged flat-topped seamount
Hadean eon
the first eon on the geologic time scale. The eon ending 3.8 billion years ago that preceded the Archean eon
the time required for on half of the atoms of a radiocative substance to decay
Hanging valley
a tributary valley that enters a clacial trought at a considerable height above the floor of the trough
a mineral's resistance to scratching and abrasion
the vertical distance between the recharcge and discharge points of a water table. Also, the source area or beginning of a valley
Headward erosion
the extension upslope of the head of a valley due to erosion
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.
a naroow, sharp-crested ridge formed by the upturned edge of a steeply dipping bed of resistant rock.
a pyramid-like peak formed by glacial action in three or more cirques surrounding a mountain summit
an elongated, uplifted block of crust bounded by faults
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.
Hot spring
a spring in which the water is 6-9 degrees C warmer than the mean annual air temperature of its locality
organic matter in soil produced by the decompoistion of plants and animals
Hydrogenous sediment
seafloor sediments consisting of minerals that crystallize from seawater. The principal example is manganese nodules
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
A chemical-weathering process in which minerals are altered by chemically reacting with water and acids
the water portion of our planet; one of the traditional subdivisions of Earth's physical environment
Hydrothermal metamorphism
chemical alterations that occur as hot, ion-rich water ciculates through fractures in rock

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