Copie de `Iowa State University - Glossary of geologic terms`
Ce glossaire n’est plus en ligne.
Le glossaire dans lequel se trouvait ce mot n’existe plus, ou le site Internet n’est (plus) pas en ligne. Vous voyez ci-dessous une copie de l’information. Il est possible que les informations ne soient plus à jour. Soyez critique en évaluant sa valeur.
|
|
|
Iowa State University - Glossary of geologic terms
Catégorie: Géographie
Date & Pays: 29/04/2015, Us.
Mots: 835
|
retrograde A succession of metamorphic conditions,each one of which is at a lower temperature and/or pressure than thepreceding one.
reverse faultA dip-slip fault on which the hangingwall block is offset upward relative to the foot wall block . comparenormal fault .
reversed polarity Time when a magnetic needle pointsto the south pole.
rhyolite A fine-grained silica-rich igneous rock, theextrusive equivalent of granite.
Richter scale A commonly used measure of earthquakemagnitude , based on a logarithmic scale. Each integral step on thescale represents a tenfold increase in the extent of ground shaking,as recorded on a seismograph.
rift(graben) A valley caused by extension of the Earth’scrust. Its floor forms as a portion of the crust moves downward alongnormal faults .
rip currentCarries excess water in the longshore currentout through the surf zone where it dissipates.
ripple marks Small waves produced by wind or watermoving across deposits of sand or silt.
ripple marks of oscillation Symmetrical ripple marksformed by oscillating movement of water such as may be found along thecoast just outside the surf zone.
rock An aggregate of one or more minerals in varyingproportions.
rock avalanche see rockslide.
rock cleavage see cleavage
rock cycle The concept of a sequence of events involvingthe formation, alteration, destruction and reformation of rocks as aresult of geologic processes and which is recurrent, returning to astarting point. It represents a closed system. compare rock system.
rock flourFinely divided rock material ground by glacialaction and fed by streams fed by melting glaciers.
rock glacier A mass of ice-cemented rock rubble foundon slopes of some high mountains. Movement is slow, averaging 30 to40 cm/yr.
rock record The history recorded in rocks.
rock system The concept of a sequence of events involvingthe formation, alteration, destruction and reformation of rocks as aresult of geologic processes. Unlike the rock cycle it is an open systemand does not return to a starting point. compare rock cycle
rock varnish A thin, shiny veneer of clay mineralsand iron and manganese oxides deposited on some rocks in a desert environment.
rock waste Angular fragments of rock. Forms a talusif abundant enough.
rockfall The sudden fall of one or more large piecesof a rock from a cliff.
rockslide(rock avalanche) A slide involving a downward andusually sudden movement of newly detached segments of bedrock sliding or slipping over an inclined surface of weakness suchas a bedding plane, fault plane, or joint surface.
roundness The degree to which a sedimentary particle’scorners and edges are rounded.
runoff The precipitation that runs directly off thesurface to stream or body of standing water.
S wave (secondary wave , shear wave) A seismic bodywave that involves particle motion from side to side, perpendicularto the direction of wave propagation. S-waves are slower than P-wavesand cannot travel through a liquid. compare P-wave .
S wave (secondary wave , shear wave) A seismic bodywave that involves particle motion from side to side, perpendicularto the direction of wave propagation. S-waves are slower than P-wavesand cannot travel through a liquid. compare P-wave .
salinizationA process by which salts accumulate insoil
salt-water invasion Displacement of fresh surface orground water by the advance of salt water.
saltation A process of sediment transport in whicha particle jumps from one point to another.
sand dune An accumulation of wind driven sand intoa distinctive shape.
sand sea A large area completely, or nearly completely,covered with sand dunes.
sandstone A clastic sedimentary rock in which the particlesare dominantly of sand size, from 0.062 mm to 2 mm in diameter.
sandstorm A blanket of wind-driven sand with an uppersurface about a meter above ground level.
sanitary land fill An artificial hill formed by therefuse of present-day civilization.
schist A strongly foliated, coarsely crystalline metamorphicrock, produced during regional metamorphism, that can readily be splitinto slabs or flakes because more than 50% of its mineral grains areparallel to each other.
schistosity The foliation in a schist, due largelyto the parallel orientation of micas.
seafloor spreading Process by which ocean floors spreadlaterally from crests of main ocean ridges. As material moves laterallyfrom the ridge, new material replaces it along the ridge crest by wellingupward from the mantle. compare continental drift , plate tectonics
seamount(guyot) A volcanic mountain on the seafloor.If flat-topped, it is a guyot.
seawallA wall at the shore and parallel to it forprotection against wave erosion
sedimentary facies An accumulation of deposits thatexhibits specific characteristics and grades laterally into other sedimentary accumulations that were formed at the same time but exhibitdifferent characteristics.
sedimentary rock Rock formed from the accumulationof sediment, which may consist of fragments and mineral grains of varyingsizes from pre-existing rocks, remains or products of animals and plants,the products of chemical action, or mixtures of these.
seismic gap A segment of an active fault zone thathas not experienced a major earthquake during a time period when most other segments of the zone have. Generally regarded as having ahigher potential for future earthquakes.
seismic records from a large number of stationsSimilarin concept to a CAT scan used for medical purposes.
seismic sea wave(tsunami) A sea wave produced by anylarge-scale, short duration disturbance on the seafloor, commonly ashallow submarine earthquake but possibly also a submarine slide orvolcanic eruption.
seismic tomography A technique for three-dimensionalimaging of the Earth’s interior by using a computer to compare the
seismograph An instrument that detects, magnifies,and records vibrations of the Earth, especially earthquakes.
seismology The study of earthquakes, and of the structureof the Earth by both natural and artificially generated seismic waves.
seismoscope An instrument that merely indicates theoccurrence of an earthquake.
self-exciting dynamo In reference to the Earth, thesuggestion that movements in the fluid core may help initiate the Earth’smagnetic field.
shadow zone A region 100º to 140º from the epicenterof an earthquake in which, due to refraction from below the core-mantleboundary, no direct seismic waves can be detected.
shale A mudstone that splits or fractures readily.
shatter cone A distinctively striated conical structurein rock, ranging from a few centimeters to a few meters in length, believedto have been formed by the passage of a shock wave following meteoriteimpact.
shear Rock deformation involving movement past eachother of adjacent parts of the rock and parallel to the plane separatingthem.
shear strength The resistance of a body to shear stress.
shear stress The stress on an object operating parallelto the slope on which it lies.
sheeting A type of jointing produced by pressure release(unloading) or exfoliation .
shield volcano A volcano in the shape of a flattenedcone, broad and low, built by very fluid flows of basaltic lava.
shock lamellae Closely spaced microscopic planes, distinctfrom cleavage planes, that occur in shock-metamorphosed minerals andare regarded as important indicators of shock metamorphism.
shock metamorphism Metamorphism induced in rock bythe passage of a high-pressure shock wave acting over a period of timefrom a few microseconds to a fraction of a minute. The only known naturalcause of shock metamorphism is the hypervelocity impact of a meteorite.
shore Seaward edge of coast between low tide and effectivewave action.
shore face The concave section of the beach from hightide mark down to the ramp between 5 and 20 m off shore.
shore platformA surface of erosion that slopes gentlyseaward from a cliff base to the low tide mark.
shoreline The line separating land and water. Fluctuatesas water rises and falls.
sialThe upper layer of the continental crust, so calledbecause it is rich in silica and aluminum oxide. compare sima.
sialic Enriched in sial.
silica Silicon dioxide (SiO2) as a pure crystallinesubstance makes up quartz and related forms such as flint and chalcedony. More generally, silica is the basic chemical constituentcommon to all silicate minerals and magmas.
silica tetrahedron The basic structural unit of whichall silicates are composed, consisting of a silicon atom surroundedsymmetrically by four oxygen atoms. The structure, therefore, has theform of a tetrahedron with an oxygen atom at each corner.
sillA tabular igneous intrusion that parallels theplanar structure of the surrounding rock.
sima The oceanic crust, also the lower layer of thecontinental crust, so called because it is enriched in silica and magnesiumoxide. compare sial.
sinkhole Depression in ground surface caused by collapseinto a cave below.
sinking stream A stream that empties into the undergroundinto a cave, usually through a sinkhole.
slate A compact, fine-grained metamorphic rock thathas slaty cleavage.
slaty cleavage A style of foliation common in metamorphosedmudstones, characterized by nearly flat, sheet-like planes of breakage,similar in appearance to a deck of playing cards. compare cleavage
slickenside A polished and smoothly striated surfacethat results from friction along a fault plane.
slide A mass movement in which material maintains continuouscontact with the surface on which it moves.
slip faceSteep face on lee side of sand dune.
slump Downward and outward rotational movement of Earthmaterials traveling as a unit or series of units.
smelting The process of removing metal from ore.
snow line The elevation at which snow persists throughoutthe year.
snowfields Expanses of snow that lie above the snowline.
soilAll unconsolidated materials above bedrock. Naturalearthy materials on the Earth’s surface, in places modified or evenmade by human activity, containing living matter, and supporting orcapable of supporting plants out of doors.
soil horizon A layer of soil that is distinguishablefrom adjacent layers by characteristic physical properties such as texture,structure, or color, or by chemical composition.
soil moisture Ground water in the zone of aeration
soil structure The combination of soil particles intoaggregates or clusters which are separated from adjacent aggregatesby surfaces of weakness.
soil textureThe physical nature of the soil, accordingto its relative proportions of sand, clay, and silt.
sole markDevelops as an irregularity on the bottomof a stratum. It is a cast of a depression on the top surface of theimmediately underlying bed.
solifluction Turbulent movement of saturated soil orsurficial debris.
sorting The range of particle sizes in a sedimentarydeposit. A deposit with a narrow range of particle sizes is termed "well-sorted."
south magnetic pole The point on the Earth where anorth seeking magnetic needle free to swing in space points directlyup.
specific gravity The ratio of the density of a materialto the density of water.
specific retention(field capacity) The amount of capillarywater retained in a soil after the drainage of gravitational moisture.
sphericityA descriptive term to describe how closea particle’s shape is to a sphere.
spit A sandy bar built out from the land into a bodyof water.
spoil Overburden or non-ore removed in mining or quarrying.
spreading axis(spreading center) A region of divergence onthe Earth's surface, as at a rift .
spreading pole A rotational pole around which a plateappears to rotate on the Earth's surface.
spring Occurs at the intersection of the water tablewith the ground surface.
stack An isolated, steep-sided, rocky mass or islandjust offshore from a rocky headland, usually on a shore platform.
stalactite An icicle-shaped accumulation of dripstonehanging from cave roof.
stalagmite A post of dripstone growing up from a cavefloor.
star duneA sand dune built by winds alternating throughseveral directions. Builds vertically rather than migrating and growinglaterally.
