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Iowa State University - Glossary of geologic terms Catégorie: Géographie Date & Pays: 29/04/2015, Us. Mots: 835

stick-slip
A jerky, sliding motion associated withfault movement.

stock
A small batholith.

stoping
A process of magmatic intrusion that involvesdetaching and engulfing pieces of the surrounding rock, so that themagma moves slowly upward.

storm surge
A ridge of high water associated with ahurricane and which floods over the shore .

strain
Change in the shape or volume of a body as aresult of stress.

strain rate
The rate at which a body changes shapeor volume as a result of stress.

strain seismograph
A seismograph that is designed todetect deformation of the ground by measuring relative displacementof two points.

stratification
The accumulation of material in layersor beds.

stratified drift
Debris washed from a glacier and laiddown in well-defined layers.

stratigraphy
The succession and age relation of layeredrocks.

stratovolcano (composite volcano)
A volcano that iscomposed of alternating layers of lava and pyroclastic material, alongwith abundant dikes and sills. Viscous, intermediate lava may flow froma central vent. Example: Mt. Fuji in Japan.

streak
The color of a mineral in its powdered form,usually obtained by rubbing the mineral against an unglazed porcelaintile to see the mark it makes. A mineral harder than the tile must bepulverized by crushing.

stream capture
see stream piracy.

stream order
A classification of the relative hierarchyof stream segments in a drainage network.

stream piracy
(stream capture) The natural diversion of theheadwaters of one stream into the channel of another stream that hasgreater erosional activity and flows at a lower level.

stream terrace
A relatively flat surface along a valley,with a steep bank separating it either from the floodplain, or froma lower terrace.

strength
The ability to withstand a stress withoutpermanent deformation.

stress
The force per unit area acting on any surfacewithin a solid; also, by extension, the external pressure which generatesthe internal force.

striations
Scratches, or small channels, gouged byglacier action. Occur on boulders, pebbles, and bedrock. Striationsalong bedrock indicate direction of ice movement.

strike
The compass direction of the intersection betweena structural surface (e.g., a bedding plane or a fault surface) andthe horizontal.

strike-slip fault
(transcurrent fault) A fault on whichthe movement is parallel to the fault’s strike.

strip mining
Open pit mining, typically for coal.

subduction zone
A narrow, elongate region in whichone lithospheric plate descends relative to another.

sublimation
The process by which matter in the solidstate passes directly to the gaseous state without first becoming liquid.

subtropical deserts
Deserts in zones of descendingair between 25 degrees and 30 degrees north and south latitude.



superimposed stream
A stream that was established ona new surface and then, as it cut downward, maintained its course despiteencountering different lithologies in the process.

superposition
A statement of relative age in layeredrocks: In a series of sedimentary rocks that has not been overturned,the topmost layer is always the youngest and the bottommost layer isalways the oldest.

surf
Produced as a wave steepens and falls forwardas the wave nears the shore.

surface of discontinuity
In sand dune formation the surfacebetween quiet air of the wind shadow and the rapidly moving air above.

surface wave
compare body wave

surging glacier
A glacier that moves rapidly (tensof meters per day) as it breaks away from the ground surface on whichit rests.

suspended load
The amount of material a stream carriesin suspension.

suspension
A method of sediment transport in whichthe turbulence of a fluid is able to keep particles supported in thefluid.

suture
The line of juncture where continental rockson two converging plates meet. Example: The region in the Himalayaswhere the Eurasian and Indian-Australian plates meet.

swash and back wash
Uprush of a wave onto the beachfollowed by the return flow of the water down the beach slope in theintervals between waves.

swells
Persistence of wind-formed waves after windceases.

syncline
A fold that is convex downward, or that hadsuch an attitude at some stage in its development. compare anticline.

taconite
A bedded ferruginous chert containing at least25% iron. A potential iron ore.

tailings
Washed or milled ore that is too poor to befurther treated.

talus
A slope built up by the accumulation of rockwaste at the foot of a cliff or ridge.

tar
A thick brown to black viscous organic liquid,too thick to migrate easily through most porous sediment.

tar sand
A sand containing tar or asphalt, from whichthe hydrocarbons may potentially be extracted by distillation.

tarn
A lake in the bedrock basin of a cirque.

tell
An artificial hill formed by the debris of successivehuman settlements.

temperate glacier
A glacier whose temperature throughoutis at, or close to, the pressure point of ice, except in winter whenit is frozen for a few meters below the surface.

tensile fracture
A fracture caused by tensional stressin a rock.

tension
A stress that tends to pull a body apart.

tephra
A general term for all pyroclastic material.

terminal moraine (end moraine)
Ridge of till markingfarthest extent of glacier.

terrane
(microplate) A fragment of the lithosphere,smaller than a plate, that forms a portion of an accreted terrane margin.

texture
The general appearance of a rock as shown bythe size, shape, and arrangement of the materials composing it.

thermal conductivity
A measure of the ability of amaterial to conduct heat.

thermal gradient
see geothermal gradient.

thermal spring
A spring whose temperature is 6.5o Cor more above mean annual air temperature.

thermoremanent magnetism
The magnetism of a mineralthat it is acquired as it cools below its Curie point.

threshold of movement
The point at which a slope orslope material crosses from a condition of stability to one of instabilityand movement begins.

thrust fault
A reverse fault on which the dip angleof the fault plane is 15 degrees or less.

thrust sheet
A body of rock above a large-scale thrustfault.

tidal delta
A delta formed at both sides of a tidalinlet.

tidal inlet
Waterway from open ocean into a lagoon.

tidal power
Power generated by harnessing the energyof tidal motion in the ocean.

till
(unstratified drift) Glacial drift composed ofrock fragments that range from clay to boulder size and randomly arranged without bedding.

topset bed
Layer of sediments deposited over surfaceof a delta, nearly horizontal and covering the tops of the inclinedforeset beds.

transcurrent fault
see strike-slip fault

transform boundary
A plate boundary in which plateson opposite sides of the boundary move past each other in opposite directions.

transform fault
A plate boundary that ideally showspure strike-slip movement. Associated with the offset segments of midoceanridges.

transported soil
A soil that has been moved from thesite of its parent rock.

transverse dune
A long, straight dune, perpendicularto direction of wind.

trap
1. Any barrier to the upward migration of petroleum,allowing it to accumulate. 2. Any dark colored extrusive igneous rock.A reference to the tendency of basalt and similar rocks to form columnarjoints.

travel time diagram
A plot of seismic wave traveltime against distance on the Earth’s surface from the epicenter of anearthquake.

travertine
(tufa) Variety of limestone which formsstalactites and stalagmites and other deposits in limestone caves (dripstone)and the mouths of hot and cold calcareous springs.

trellis drainage
A drainage pattern in which a streamand its tributaries resemble the pattern of a vine on a trellis.

trench
Along, narrow, steep-walled, often arcuate depressionin the ocean floor, much deeper than the adjacent ocean and associated with a subduction zone .

triangulation
The method of locating an epicenter bydetermining how far it lies from three widely separated seismographs.

troughs and bars
Linear features in unconsolidatedsediments at the foot of the shoreface, the result of breaking waves.

TRU
see Low level nuclear waste.

truncated spur
The beveled end of a ridge separatingtwo valleys where they join a larger glaciated valley. Glacier of mainvalley has eroded back the end of the ridge.

tufa
see travertine .

tuff
A general term for all consolidated pyroclasticrock. Not to be confused with tufa.

turbidite
Sedimentary deposit settled out of turbidwater carrying particles of widely varying grade size. Characteristicallydisplays graded bedding.

turbulent flow
Fluid flow in which the flow lines areconfused and mixed. Fluid moves in eddies and swirls. compare laminarflow.

U-shaped valley
A valley carved by glacier erosionand whose cross-valley profile has steep sides and a nearly flat floor,suggestive of a large letter "U".

U-shaped valley
A valley carved by glacier erosionand whose cross-valley profile has steep sides and a nearly flat floor,suggestive of a large letter "U".

unconformity
A buried erosion surface separating tworock masses.

uniformitarianism
The principle that applies to geologyour assumption that the laws of nature are constant As originally used it meant that the processes operating to change the Earth in thepresent also operated in the past and at the same rate and intensityand produced changes similar to those we see today. The meaning hasevolved and today the principle of uniformitarianism acknowledges thatpast processes, even if the same as today, may have operated at differentrates and with different intensities than those of the present. Theterm "actualism" is sometimes used to designate this latermeaning.

unloading
The release of confining pressure associatedwith the removal of overlying material. May result in expansion of rock,accompanied by the development of joints or sheeting .

USDA Soil Classification System
A classification ofsoils on the basis of the processes and conditions by which they form.compare Comprehensive Soil Classification System.

valley glacier
(alpine glacier, mountain glacier )Streams of ice that flow down valleys in mountainous areas.

valley train
Outwash plain contained within valleywalls.

varve
A pair sedimentary units, one coarse-grained,the other fine-grained, interpreted as representing one year of sedimentation.

velocity
Distance of travel in unit of time

velocity profile
A plot of seismic velocity againstdepth in the Earth.

ventifact
A pebble, cobble, or boulder faceted by winddriven sand.

vesicle
A cavity in a lava, formed by the entrapmentof a gas bubble during solidification of the lava.

vesicular
A textural term applied to an igneous rockcontaining abundant vesicles, formed by the expansion of gases initiallydissolved in the lava.

viscosity
The internal resistance to flow in a liquid.

volcanic ash
The dust-sized, sharp-edged, glassy particlesresulting from an explosive volcanic eruption.

volcanic cinder
A pyroclastic fragment, 0.5 to 2.5cm in diameter, formed as magma spatters into the air during a volcaniceruption and cools as it falls to Earth.

volcano
A vent in the surface of the Earth, from whichlava, ash, and gases erupt, forming a structure that is roughly conical.

volcanogenic massive sulfide deposit
A mineral depositof metallic sulfides formed directly through processes associated withvolcanism, commonly in a submarine setting.