T Index Glossary geology Science
T Index Glossary geology Science
Taiga
A moist subarctic coniferous forest that begins where the tundra ends and is dominated by spruces and firs.
Temperature Inversion
An increase in temperature with height above the Earth's surface, a reversal of the normal pattern.
Territory
A specific area or portion of the Earth's surface; not to be confused with region.
Tertiary Sector
That portion of a region's economy devoted to service activities (e.g., transportation, retail and wholesale operations, insurance).
talus slope
The large pile of rocky boulders that accumulates at the foot of a cliff, typically by the mechanical-weathering process of frost-wedging.
tectonic creep
The almost constant movement of certain fault blocks that allows strain energy to be released without major earthquakes.
thermal contraction
A form of mechanical weathering in which cold causes a mineral's crystal structure to contract.
translatory motion
the movement of water over a significant distance in the direction of a wave.
Threshold
The minimum-sized market for an economic activity. The activity will not be successful until it can reach a population larger than this threshold size.
Terrestrial sediment
A deposit of sediment that accumulated above sea level in lakes, alluvial fans, floodplains, moraines, etc., regardless of its present elevation.
Thalweg
A sinuous imaginary line following the deepest part of a stream.
Thermal conductivity
A measure of a rock's capacity for heat conduction.
Thermonuclear reaction
A reaction in which atomic nuclei fuse into new elements with a large release of heat; especially a reaction that is self-sustaining. Occasionally used to include fission reactions as well.
Thermoremnent magnetization
A permanent magnetization acquired by igneous rocks in the presence of the Earth's magnetic field as they cool through the Curie point.
Time scale
The division of geologic history into eras, periods, and epochs accomplished through stratigraphy and paleontology.
Topset bed
A horizontal sedimentary bed formed at the top of a delta and overlying the foreset beds.
Transition element
Elements of atomic number 21 to 29, 38 to 46, and 71 to 78, whose second outermost electron shell is only partially filled.
Travel-time curve
A curve on a graph of travel time versus distance for the arrival of seismic waves from distant events. Each type of seismic wave has its own curve.
Township and Range
The rectangular system of land subdivision of much of the agriculturally settled United States west of the
Transferability
The extent to which a good or service can be moved from one location to another; the relative capacity for spatial interaction.
Transhumance
The seasonal movement of people and animals in search of pasture. Commonly, winters are spent in snow-free lowlands and summers in the cooler uplands.
Tree Line
Either the latitudinal or elevational limit of normal tree growth. Beyond this limit, closer to the poles or at higher or lower elevations, climatic conditions are too severe for such growth.
Tropics
Technically, the area between the Tropic of Cancer (21-1/2 N latitude) and the Tropic of Capricorn (21-1/2 S latitude), characterized by the absence of a cold season. Often used to describe any area possessing what is considered to be a hot, humid climate.
Tundra
A treeless plain characteristic of the arctic and subarctic regions.
Tableland
An area of elevated land with a nearly level surface.
Tar Sand
A sandstone that contains asphalt within its pore spaces.
Talus
An accumulation of angular rock debris at the base of a cliff or steep slope that was produced by physical weathering.
Tectonics
The study of processes that move and deform Earth's crust.
Terminal Moraine
A mound of unsorted glacial till that marks the furthest advance of a glacier.
Terrestrial Planet
One of the four rocky planets closest to the sun, which include Mars, Venus, Earth and Mercury.
Terrigenous Sediment
Sediment that is derived from the weathering of rocks which are exposed above sea level.
Texture
The visible characteristics of a rock which include its grain size, grain orientation, rounding, angularity or presence of vesicles.
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
A reverse fault that has a dip of less than 45 degrees.
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
A broad flat area, very close to sea level that is flooded and drained with each rise and fall of the tide.
Tidal Wave
A term that is incorrectly used in reference to a tsunami. Tsunamis have nothing to do with the tides.
tarn
A deep, typically circular lake that forms when a cirque glacier melts.
tension
Stress that stretches or extends rocks, so that they become thinner vertically and longer laterally. Tension may be caused by divergence or rifting.
tephra
plural noun\Pyroclastic materials that fly from an erupting volcano through the air before cooling, and range in size from fine dust to massive blocks.
terminus
The outer margin of a glacier.
theory
A comprehensive explanation of a given set of data that has been repeatedly confirmed by observation and experimentation and has gained general acceptance within the scientific community but has not yet been decisively proven. See also hypothesis and scientific law.
thermal expansion
A form of mechanical weathering in which heat causes a mineral's crystal structure to enlarge.
thermal plume
A vertical column of upwelling mantle material 100 to 250 kilometers in diameter, that rises from beneath a continent or ocean and can be perceived at the Earth's surface as a hot spot. Thermal plumes carry enough energy to move a plate, and they may be found both at plate boundaries and plate interiors.
tidal bore
A turbulent, abrupt, wall-like wave that is caused by a flood tide.
tide
1. The cycle of alternate rising and falling of the surface of an ocean or large lake, caused by the gravitational pull of the Sun and especially Moon in interaction with the Earth's rotation. Tides occur on a regular basis, twice every day on most of the Earth. 2. A single rise or fall within this cycle.
transform motion
The movement of two adjacent lithospheric plates in opposite directions along a parallel line at their common edge. Transform motion often causes earthquakes.
transition zone
The seismic discontinuity located in the upper mantle just beneath the asthenosphere and characterized by a marked increase in the velocity of seismic waves.
translatory
Of, concerning, or being the movement of water over a significant distance in the direction of a wave.
transport medium
A natural agent, such as water, air, or ice, that moves a particle or particles from one location on the Earth's surface to another.
transverse dune
One of a series of dunes having an especially steep slip face and a gentle windward slope and standing perpendicular to the prevailing wind direction and parallel to each other. Transverse dunes typically form in arid and semi-arid regions with plentiful sand, stable wind direction, and scarce vegetation. A transverse dune may be as much as 100 kilometers long, 200 meters high, and three kilometers wide.
trunk stream
A large stream into which tributaries carry water and sediment.
Till
An unsorted sediment deposited directly by a glacier and not reworked by meltwater.
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.
Trace Element
An element that is present in very small quantities.
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
A strike-slip fault that connects offsets in a mid-ocean ridge.
Transgression
An advance of the sea over land areas. Possible causes include a rise in sea level or subsidence.
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
Travertine
Calcium carbonate deposits which form in caves and around
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
A long, narrow, deep depression in the ocean floor that parallels a convergent boundary involving at least one oceanic plate.
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.
Tsunami
plural tsunami-A vast sea wave caused by the sudden dropping or rising of a section of the sea floor following an earth- quake. Tsunami may be as much as 30 meters high and 200 kilometers long, may move as fast as 250 kilometers an hour, and may continue to occur for as long as a few days.
- A large sea wave normally produced by sudden movement of the ocean floor caused by an earthquake or volcanic eruption. These waves can travel at high speeds across an ocean basin and cause great destruction when they reach land.
Topography
The shape of Earth's surface or the geometry of landforms in a geographic area.
- The physical features of a place; or the study and depiction of physical features, including terrain relief.
tertiary wastewater treatment
selected biological, physical, and chemical separation processes to remove organic and inorganic substances that resist conventional treatment practices; the additional treatment of effluent beyond that of primary and secondary treatment methods to obtain a very high quality of effluent. The complete wastewater treatment process typically involves a three-phase process:
-(1) First, in the primary wastewater treatment process, which incorporates physical aspects, untreated water is passed through a series of screens to remove solid wastes;
-(2) Second, in the secondary wastewater treatment process, typically involving biological and chemical processes, screened wastewater is then passed a series of holding and aeration tanks and ponds; and
-(3) Third, the tertiary wastewater treatment process consists of flocculation basins, clarifiers, filters, and chlorine basins or ozone or ultraviolet radiation processes
thermoelectric power water use
water used in the process of the generation of thermoelectric power. Power plants that burn coal and oil are examples of thermoelectric-power facilities.
transpiration
process by which water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, such as leaf pores. See evapotranspiration .
tributary
A stream that supplies water to a larger stream.
- a smaller river or stream that flows into a larger river or stream. Usually, a number of smaller tributaries merge to form a river.
turbidity
the amount of solid particles that are suspended in water and that cause light rays shining through the water to scatter. Thus, turbidity makes the water cloudy or even opaque in extreme cases. Turbidity is measured in nephelometric turbidity units (NTU).
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.
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
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 "Density Current".
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.)