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Iowa State University - Glossary of geologic terms
Catégorie: Géographie
Date & Pays: 29/04/2015, Us.
Mots: 835
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dip slip fault A fault on which the movement is parallelto the dip of the fault plane.
directed pressure Pressure applied predominately inone direction, rather than uniformly.
discharge In a stream, the volume of water passingthrough a channel in a given time.
disconformity An unconformity in which the beds abovethe unconformity are parallel to the beds below the unconformity.
discordantCutting across surrounding strata.
disintegration(mechanical weathering) The processesof weathering by which physical actions such as frost wedging breakdown a rock into fragments, involving no chemical change.
dissolutionA chemical reaction in which a solid materialis dispersed as ions in a liquid. Example: Halite (NaCl) undergoes dissolutionwhen placed in water.
dissolved load Amount of material water carries insolution.
distributary channels Stream channels that fan out from theupstream point of the delta and carry the sediments that build the delta.
divergent boundary Boundary between two crustal plates thatare pulling apart.
dolostoneA carbonate rock made up predominately ofthe mineral dolomite, CaMg(C03)2.
dome An uplift or anticlinal structure, roughly circularin its outcrop exposure, in which beds dip gently away from the centerin all directions.
drag fold A minor fold produced within a weak bed oradjacent to a fault by the movement of surrounding rocks in oppositedirections.
drainage basinThe area from which a stream and itstributaries receives its water.
drainage divide The line that separates one drainagebasin from another.
drift Glacial deposits laid down directly by glaciersor laid down in lakes, ocean, or streams as result of glacial activity.
dripstoneCalcium carbonate deposited from solutionas water enters a cave through the zone of aeration. Forms stalactites,stalagmites and other cave deposits.
drumlin Streamlined hill, largely of till, with bluntend pointing into direction from which ice moved. Occur in clusterscalled drumlin fields.
dry farming Farming without irrigation in drylands.
drylandsA general term for semiarid and desert lands.
ductile Structural behavior in which a material deformspermanently without fracturing.
dust bowl An area subject to dust storms, especiallysouth central United States.
dust devil A small, dust-bearing whirlwind.
dust stormLarge volume of dust-sized particles liftedhigh into the atmosphere.
Earth system System involving continuous interactionof the solid Earth, the atmosphere, the oceans and living things.
earthflow A form of slow, but perceptible, mass movement,with high content of water and rock debris. Lateral boundaries are well-definedand the terminus is lobed. With increasing moisture content grades intoa mudflow.
eccentricity of the Earths orbit A measure of thecircularity of the Earth's orbit. It varies in cycles of about 100,000and 400,000 years.
elastic Non-permanent structural deformation duringwhich the amount of deformation (strain) is proportional to the stress.
elastic rebound The statement that movement along afault is the result of an abrupt release of a progressively increasingelastic strain between the rocks on either side of the fault.
elasticity The tendency for a body to return to itsoriginal shape and size when a stress is removed.
electron A fundamental unit of matter, negatively chargedand disposed in a cloud surrounding the nucleus of an atom.
electron capture Nuclear decay in which a proton inthe nucleus acquires an electron from the outer cloud of the atom’selectrons. This converts the proton to a neutron, reduces the numberof protons in the nucleus by one and atomic number of the original elementby one. Atomic mass number remains constant because the total numberof protons and neutrons is unchanged.
electron shell A characteristic energy level with whichan electron is associated. Electrons occupy discrete shells within thecloud surrounding an atom’s nucleus. These may be thought of, loosely,as if they represented orbits at distinct heights above the nucleus.
element see chemical element
end moraine see terminal moraine.
eon The primary division of geologic time which are,from oldest to youngest, the Hadean, Archean, Proterozoic, and Phanerozoiceons.
epicenter The point on the Earth’s surface that isdirectly above the focus of an earthquake.
epoch A division of geologic time next shorter thana period. Example: the Pleistocene epoch is in the Quaternary period.
equilibrium line On a glacier the line separating thezone of accumulation from the zone of ablation .
era A division of geologic time next smaller than theeon and larger than a period. Example: The Paleozoic era is in the Phanerozoiceon and includes, among others, the Devonian period.
erratic A stone or boulder, glacially transported fromplace of origin and left in an area of different bedrock composition.
eskerA winding ridge of stratified drift . Forms ina glacial tunnel and, when ice melts, stands as ridge up to 15 m highand kilometers in length.
ETP curve see Milankovitch curve .
eustatic change in sea level A worldwide change in sea level,such as caused by melting glaciers.
eutrophication The process of aging of lakes by theaddition of nutrients.
evaporite A mineral or rock deposited directly froma solution (commonly seawater) during evaporation. For example, gypsumand halite are evaporite minerals.
exfoliation The process by which concentric scales,plates, or shells of rock are stripped or spall from the bare surfaceof a large rock mass.
exfoliation dome A large dome-shaped form that developsin homogeneous crystalline rocks as the result of exfoliation.
exotic river A river that is able to maintain its flowthrough a desert because of water received from outside the desert.
extrusive Pertaining to igneous rocks or features formedfrom lava released on the Earth’s surface.
facies see metamorphic facies , sedimentary facies
failed rift A rift emanating from a plate triple junctionalong which minimal divergence has taken place.
fall When applied to mass movement of material refersto free fall of material moving without contact with the surface.
fault The surface of rock rupture along which therehas been differential movement of the rock on either side.
fault gouge Soft, uncemented, pulverized clay-likematerial found along some faults.
ferromagnesian Containing iron and magnesium, appliedto the mafic minerals. Example: olivine.
fetch Distance over which wave-forming winds blow.
field capacity see specific retention.
fiery cloud see nuée ardente .
firn(névé) Granular ice formed by the recrystallizationof snow. Intermediate between snow and glacier ice.
fission The spontaneous or induced splitting, by particlecollision, of a heavy atomic nucleus into a pair of fragments plus someneutrons. Controlled induced fission can be used as a source of nuclearpower.
fission track dating Dating of minerals by fissiontracks, damage tracks left in a mineral by spontaneous alpha emissions.
fissure eruption An eruption of lava that takes placefrom a fracture, usually without producing a cone.
fjord Glaciated valleys now flooded by the sea.
flash flood A flood that rises and falls very rapidly.
flashy stream A stream with a high, short flood peakand short lag time.
flint A variety of chert , often black because of includedorganic matter.
flood Peak flow that tops the banks of a stream channel.
flood recurrence interval The number of years of recordplus 1 divided by the rank of each maximum annual flood.
floodplain Area bordering a stream over which waterspreads when the stream tops its channel banks.
flow When applied to mass movement, refers to a chaoticmovement of material in continuous contact with the ground surface,commonly involving a moderate to high amount of water.
flow folding A fold formed in relatively fluid rocksthat have flowed toward a synclinal trough.
flowstone General term for deposits formed by drippingand flowing water on walls and floors of caves.
fluid inclusion A tiny cavity in a crystal, commonly1 to 100 microns in diameter, containing liquid and/or gas. Formed bythe entrapment of fluid during the growth or subsequent deformationof the crystal.
focus The point within the Earth which is the centerof an earthquake, at which strain energy is first released and convertedto elastic wave energy.
fold and thrust mountains Mountains, characterizedby extensive folding and thrust faulting, that form at convergent plateboundaries on continents.
foliation A planar structure that develops in metamorphicrocks as a result of directed pressure.
foot wall blockThe body of rock that lies below aninclined fault plane. compare hanging wall block
foreset bed Inclined layers of sediment deposited onthe advancing margin of a growing delta or along the slip face of asand dune.
foreshock A minor tremor that precedes an earthquake.An increase in seismicity may signal that a major release of strainenergy is about to occur.
foreshore Lies between low and high tide marks.
formation water The water, held in pore volume in sedimentaryrocks, that has persisted with little change in composition since itwas buried with the sediment.
fossil Evidence in rock of the presence of past life,such as a dinosaur bone, an ancient clam shell, or the footprint ofa long-extinct animal.
fossil fuel A hydrocarbon (coal or petroleum) thatcan be extracted from the Earth for use as a fuel. Fossil fuels arenon-renewable energy sources.
fractional crystallization A sequence of crystallizationfrom magma in which the early-formed crystals are prevented from reactingwith the remaining magma, resulting in a magma with an evolving chemicalcomposition.
fragipan A dense layer of soil, containing silt andsand but no organic matter and little clay, whose extreme hardness andimpermeability are due primarily to compaction. compare caliche , claypan,hardpan.
free oscillation A vibration of a body such as a bellor the Earth that continues without further influence after an initialevent.
fringing reef A coral reef attached directly to themainland.
frost wedging A type of disintegration in which jointedrock is forced apart by the expansion of water as it freezes in fractures.
fusion The combination of two light nuclei to forma heavier nucleus, with the accompanying release of energy. This isthe source of energy in a hydrogen bomb. If it could be controlled,it could serve as an alternative to fission in nuclear power generation.
gabbro A coarse-grained igneous rock, chemically equivalentto a basalt.
gardening The constant and slow churning of the lunarregolith as the result of meteorite impacts.
geanticline An anticlinal structure presumed to formin the context of geosynclinal evolution. Not in current use since thedevelopment of plate tectonic theory.
geode Roughly spherical, hollow or partially hollowaccumulation of mineral matter. A few centimeters to nearly 0.5 m indiameter. Outer layer of chalcedony lined with crystals that projecttoward the hollow center. Crystals, often perfectly formed, usuallyquartz although calcite and dolomite and – more rarely – other minerals.Most commonly occur in limestone, and less often in shale.
geologic column The arrangement of rock units in theproper chronological order from youngest to oldest.
geologic time scale The chronological sequence of unitsof Earth time.
geology The science that deals with the study of theplanet Earth–the materials of which it is made, the processes thatact to change these materials from one form to another, and the historyrecorded by these materials; the forces acting to deform the outer layersof the Earth and create ocean basins and continents; the processes thatmodify the Earth’s surface; the application of geologic knowledge tothe search for useful materials and the understanding of the relationshipof geologic processes to people.
geosyncline A downwarping of the Earth’s crust, eitherelongate or basin-like, measured in scores of kilometers, in which sedimentaryand volcanic rocks accumulate to thicknesses of thousands of meters.Not in current use since the development of plate tectonic theory.
geothermal energy Heat extracted from the Earth foruse as an power source.
geothermal gradient The rate at which temperature increaseswith depth below the surface.
