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Geological Terms Beginning With "T"



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Tableland

Tableland

An area of elevated land with a nearly level surface.

Tar Sand

Tar Sand

Also known as "oil sand". A porous sand or sandstone that contains asphalt or bitumen within its pore spaces. Sometimes the name "oil sand" is used for a deposit in which the hydrocarbon is in a liquid form and the name "tar sand" is reserved for those deposits in which the hydrocarbon is in the form of solid asphalt or bitumen.

Talus

Talus

An accumulation of angular rock debris at the base of a cliff or steep slope that was produced by physical weathering.

Tectonics

Tectonics

The study of processes that move and deform Earth's crust.

Terminal Moraine

Terminal Moraine

A mound of unsorted glacial till that usually crosses a valley and marks the furthest advance of a glacier. Also called an "end moraine". The photo shows the terminal moraine of the Nellie Juan Glacier near Prince William Sound, Alaska. The two-mile long lagoon between the terminal moraine and the glacier's terminus is filled with seawater.

Terminal Moraine

Terminus

The lower end of a glacier, often called the "snout". The photo shows the terminus of the Pedersen Glacier

Terrestrial Planet

Terrestrial Planet

One of the four rocky planets closest to the sun, which include Mars, Venus, Earth and Mercury.

Terrigenous Sediment

Terrigenous Sediment

Sediment that is derived from the weathering of rocks which are exposed above sea level.

Texture

Texture

The visible characteristics of a rock which include its grain size, grain orientation, rounding, angularity or presence of vesicles.

Thermal Pollution

Thermal Pollution

Water quality is not defined by chemistry alone. If natural waters are withdrawn for use they should be returned to the environment at approximately the same temperature. An increase or decrease in temperature can have an adverse effect upon plants, animals and chemical balances. Returning water to a stream at a different temperature than it was withdrawn is known as thermal pollution. For example, coal-fired power plants use water in the production of steam that turns turbines. That water is then cooled in the large cooling towers before it is returned to the environment.

Thrust Fault

Thrust Fault

A reverse fault that has a dip of less than 45 degrees.

Tidal Current

Tidal Current

Currents of water that are produced in response to a rising or falling tide. These currents can flow into or out of a bay, delivering the rising water or removing the falling water.

Tidal Flat

Tidal Flat

A broad flat area, very close to sea level that is flooded and drained with each rise and fall of the tide.

Tidal Wave

Tidal Wave

A term that is incorrectly used in reference to a tsunami. Tsunamis have nothing to do with the tides.

Till

Till

An unsorted sediment deposited directly by a glacier and not reworked by meltwater.

toe

Toe

A bulge of soil that develops at the base of a landslide. It occurs where the moving mass overruns the surface exposure of the slip plane. Often people see a mound of soil develop on a slope and grade it level or remove it. Removing the toe of a slide can cause the slide to accerate because the toe provides support.

Topographic Map

Topographic Map

A map that shows the change in elevation over a geographic area through the use of contour lines. The contour lines trace points of equal elevation across the map. See also: contour line and contour map.

Topography

Topography

The shape of Earth's surface or the geometry of landforms in a geographic area.

Trace Element

Trace Element

An element that is present in very small quantities.

Trachyte

Trachyte

A fine-grained volcanic rock that contains large amounts of potassium feldspar.

Traction

Traction

Transport of sediment by wind or water in which the sediment remains in contact with the ground or bed of the stream, moving by rolling or sliding. (See suspension and saltation for comparison.)

Transform Fault

Transform Fault

A strike-slip fault that connects offsets in a mid-ocean ridge.

Transgression

Transgression

An advance of the sea over land areas. Possible causes include a rise in sea level or subsidence.

Translational slide

Translational Slide

A slope failure in which the moving mass travels along a roughly planar surface with little rotation or backward tilting.

Transmission Pipeline

Transmission Pipeline

A pipeline that carries natural gas from a region where it is produced to a region where it is stored or consumed.

Transpiration

Transpiration

A process of plants removing water from the soil and releasing it into the atmosphere through their leaves.

>Transverse Dunes

Transverse Dunes

Sand dunes that are oriented at right angles to the direction of the prevailing wind. These form where vegetation is sparse and the sand supply is abundant.

Trap

Trap

A sedimentary or tectonic structure where oil and/or natural gas has accumulated. These are structural highs where a porous rock unit is capped by an impermeable rock unit. Oil and gas trapped within the porous rock unit migrate to a high point in the structure because of their low density.

Travertine

Travertine

Calcium carbonate deposits which form in caves and around hot springs where carbonate-bearing waters are exposed to the air. The water evaporates, leaving a small deposit of calcium carbonate.

Trellis Drainage

Trellis Drainage

A drainage pattern in which streams intersect at right angles. This forms in areas of long parallel valleys such as in folded mountain belts. Rivers occupy the valleys and tributary streams join them at right angles.

Trench

Trench

A long, narrow, deep depression in the ocean floor that parallels a convergent plate boundary involving at least one oceanic plate.

Triple Junction

Triple Junction

A point where three lithospheric plates meet. Triple junctions can be areas of unusual tectonic activity due to the differential motions of the three intersecting plates.

Triple Junction

Troglobites

small creatures that have adapted to a permanent life in a cave. They are so well adapted to life in a cave that they would be unable to survive in the surface environment. To survive in the darkness troglobites have highly-developed senses of hearing, touch and smell.

Tsunami

Tsunami

A large wave that is produced by the sudden displacment of a large volume of water. This type of displacement is usually caused by an earthquake, but can also be produced by: submarine landslides, subaerial landslides, explosive volcanic eruptions, iceberg calving, atmospheric pressure changes or asteroid impacts. These events suddenly depress or elevate a large volume of water, then gravity causes the energy of that displacemenet to propagate away from the source. Most tsunamis originate in the ocean but they can be produced in smaller bodies of water. Tsunamis travel at high speeds for great distances (often crossing ocean basisns) and can cause great destruction when they reach land.

Tuff

Tuff

A rock composed of pyroclastic materials that have been ejected from a volcano. In many instances these fragments are still hot when they land, producing a "welded" rock mass. Picture of Tuff.

Turbidite

Turbidite

A vertical sequence of sediments deposited by a turbidity current. Because the largest particles of the current settle first a turbidite will be graded deposits with coarsest grain sizes at the bottom and finer grain sizes going upwards.

Turbidity Current

Turbidity Current

A mixture of sediment particles and water that flows down the continental slope. These high density currents can reach great speeds and generally erode loose sediments from the seafloor beneath them. See also: Density Current.

Turbulent Flow

Turbulent Flow

An irregular state of fluid flow in which the particle paths cross one another and may even travel in opposing directions. (Compare with Laminar Flow.)

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