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Iowa State University - Geology terms Category: Education > University Date & country: 18/11/2013, USA Words: 782

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 by the size, shape, and arrangement of the materials composing it.

The present is the key to the past
A shorthand reference to the principle of uniformitarianism .

thermal conductivity
A measure of the ability of a material to conduct heat.

thermal gradient
see geothermal gradient.

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

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

threshold of movement
The point at which a slope or slope material crosses from a condition of stability to one of instability and movement begins.

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

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

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

tidal inlet
Waterway from open ocean into a lagoon.

tidal power
Power generated by harnessing the energy of tidal motion in the ocean.

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

topset bed
Layer of sediments deposited over surface of a delta, nearly horizontal and covering the tops of the inclined foreset beds.

transcurrent fault
see strike-slip fault

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

transform fault
A plate boundary that ideally shows pure strike-slip movement. Associated with the offset segments of midocean ridges.

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

transverse dune
A long, straight dune, perpendicular to 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 columnar joints.

travertine
(tufa) Variety of limestone which forms stalactites 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 stream and its tributaries resemble the pattern of a vine on a trellis.

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

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

troughs and bars
Linear features in unconsolidated sediments 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 separating two valleys where they join a larger glaciated valley. Glacier of main valley has eroded back the end of the ridge.

tufa
see travertine .

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

turbidite
Sedimentary deposit settled out of turbid water carrying particles of widely varying grade size. Characteristically displays graded bedding.

turbulent flow
Fluid flow in which the flow lines are confused and mixed. Fluid moves in eddies and swirls. compare laminar flow.

unconformity
A buried erosion surface separating two rock masses.

uniformitarianism
The principle that applies to geology our assumption that the laws of nature are constant As originally used it meant that the processes operating to change the Earth in the present also operated in the past and at the same rate and intensity and produced changes similar to those we see today. The meaning has evolved and today the principle of unif...

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

unstratified drift
see till

USDA Soil Classification System
A classification of soils 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 valley walls.

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 against depth in the Earth.

ventifact
A pebble, cobble, or boulder faceted by wind driven sand.

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

vesicular
A textural term applied to an igneous rock containing abundant vesicles, formed by the expansion of gases initially dissolved in the lava.

viscosity
The internal resistance to flow in a liquid.

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

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

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

Wadati-Benioff zone
An inclined plane, roughly coincident with a subduction zone, along which the foci of earthquakes cluster.

Waste Isolation Pilot Plant
A pilot plant near Carlsbad, New Mexico, for the storage of low level nuclear waste.

water gap
A gap in a ridge or mountain through which a stream flows.

water power
Power generated through the agency of moving water.

waterfall
The perpendicular or very steep descent of a stream.

wave base
A depth equal to one half the wave length of waves in deep water, below which stirring due to wind is negligible.

wave crest
The top of a wave.

wave height
The vertical distance between the crest and adjacent trough of a wave.

wave trough
The low spot between two successive waves.

weathering
The process by which Earth materials change when exposed to conditions at or near the Earth

well
An artificial intersection of the surface and the water table.

Wilson Cycle
The opening and closing of ocean basins through plate tectonics.

wilting point
The stage at which all water available to plants has been used.

wind farm
An area in which a large number of windmills have been erected to generate electrical power.

wind gap
An abandoned water gap.

wind power
Power generated by using the force of the wind.

wind shadow
An area of quiet air in lee of an obstacle. Zone of sand accumulation in lee of sand dune.

xenolith
see inclusion

yardang
Sharp, irregularly-crested ridges carved by wind and oriented parallel to wind.

yazoo-type river
A tributary stream unable to enter a main stream because of natural levees along the main stream. It flows in a backswamp area, parallel to the main stream until it finds an entry to the main stream.

yield point
The stress limit at which permanent deformation takes place in a non-brittle material.

Yucca Mountain
Site Site in Nevada proposed for the storage of high level nuclear waste.

zone of ablation
The area of wastage in a glacier.

zone of accumulation
1. The B horizon in a residual soil. 2. The area in which ice accumulates in a glacier.

zone of aeration
Zone immediately below the ground surface within which pore spaces are partially filled with water and partially filled with air.

zone of fracture
The near surface zone in a glacier that behaves like a brittle substance.

zone of leaching
The upper horizons in a soil, through which gravitational moisture travels, removing soluble decomposition products.

zone of saturation
The zone below the zone of aeration in which all pore spaces are filled with water.

m
(clastic wedge) A mappable body of rock characterized by blocks and fragments of all sizes, embedded in a sheared matrix. A tectonic m

n
see firn.

P- wave
(primary wave, compressional wave) A seismic body wave that involves particle motion, alternating compression and expansion, in the direction of wave propagation. It is the fastest seismic wave. compare S-wave.

S wave
(secondary wave , shear wave) A seismic body wave that involves particle motion from side to side, perpendicular to the direction of wave propagation. S-waves are slower than P-waves and cannot travel through a liquid. compare P-wave .

X-ray diffraction
The diffraction of a beam of X-rays by the three dimensional periodic array of atoms in a crystal structure . The identity and arrangement of atomic in the structure can be determined by interpreting the angles at which X-rays are scattered by the structure and the intensities of scattered beams.