Geological Glossary - T

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T-phase	Tertiary wave, a late-arriving short-period phase often recorded at stations of island or coastal regions, containing energy that travels through a layer of water in the ocean known as the SOFAR channel. Can be caused by earthquake or submarine volcanic eruption.
TEM	Transient Electromagnetic Method in which the primary energizing field is a repetitive pulse.
Tertiary	A period in the geologic time scale that spans from 65 to 1.6 million years ago.
Thalweg	A sinuous imaginary line following the deepest part of a stream.
Triassic	A period in the geologic time scale that spans from 245 to 208 million years ago.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
tableland	A large elevated region with a relatively low relief surface.
talc	Magnesium silicate mineral, with water. Commonly called soapstone. Very soft and platy, like mica. Can be easily carved with a knife. Generally in very fine grained masses.
talus	Pile of rock rubble below a cliff or chute. Talus slope is a common usage although it is redundant because the term talus actually includes the concept of a slope.
tar sand	A sandstone containing the densest aspbaltic components of petroleum - the end-product of evaporation of volatile components or of some thickening process.
tarn	Small lake left by the retreat of a glacier. May fill a basin formed by a moraine dam or eroded by the glacier into bedrock.
tectonically active	A term used to describe regions that are strongly affected by movement of Earth's tectonic plate. Earthquakes and volcanoes are common features in these regions.
tectonics	The study of the movements and deformation of the crust on a large scale, including epeirogeny, metamorphism, folding, faulting, and plate tectonics.
teleseism	An earthquake that is distant (usually more than 20 degrees) from the recording station.
telluric currents	Natural electric currents that flow in the ground.
tephra	General term for all sizes of particles ejected into the air during volcanic eruption. Includes particles as tiny as volcanic ash and as large as bomb and blocks (= pyroclastic).
terminal moraine	A sinuous ridge of unsorted glacial till deposited by a glacier at the line of its farthest advance.
terminus	The downvalley end of a glacier. It is sometimes referred to as the glacier snout.
terrace	Level or near-level area of land, generally above a river or ocean and separated from it by a steeper slope. A river terrace is made by the river at some time in the past when the river flowed at a higher level. It A terrace may be made of river deposits such as gravel or sand, or it could be cut by the river on bedrock. A glacial terrace or outwash terrace is similar but is formed by a stream or river from a glacier upstream.
terrane	A rock formation or assemblage of rock formations that share a common geologic history. A geologic terrane is distinguished from neighboring terranes by its different history, either in its formation or in its subsequent deformation and/or metamorphism. Terranes are separated by fault. An exotic terrane is one that has been transported into its present setting from some distance.
terrestrial	A deposit of sediment that accumulated above sea level in lakes, alluvial fans, floodplains, moraine, etc., regardless of its present elevation.
terrestrial planet	"A planet similar in size and composition to the Earth; especially Mars, Earth, Venus, and Mercury. "
texture, rock	The rock characteristics of grain or crystal size, size variability, rounding or angularity, and preferred orientation.
thermal aureole	Zone of rock around an igneous intrusion that has been altered or metamorphosed by heat from the hot magma. The rock in the zone is baked.
thermal conductivity	A measure of a rock's capacity for heat conduction.
thermal expansion	The property of increasing in volume as a result of an increase in internal temperature.
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. "
thermophile	Solute diffuses into warmer bottom waters.
thermoremanent magnetization	A permanent magnetization acquired by igneous rocks in the presence of the Earth's magnetic field as they cool through the Curie point.
tholeiite	Basalt with a characteristic chemical composition found in an island or continental volcanic arc (also a high-K tholeiite).
tholelite	Relatively silica-rich and alkali-poor basaltic rock containing intermediate to calcic, plagioclase, clinopyroxene, and low-Ca pyroxene.
thrust fault	A dip-slip fault in which the upper block above the fault plane moves up and over the lower block, so that older strata are placed over younger.
thrust plate	Slab of rock, generally on the scale of a mountain or more, bounded by two thrust fault.
tidal current	A horizontal displacement of ocean water under the gravitational influence of Sun and Moon, causing the water to pile up against the coast at high tide and move ourward at low tide.
tidal flat	A broad, flat region of muddy or sandy sediment, covered and uncovered in each tidal cycle.
tide	The rise and fall of the water in the oceans due to the gravitational pull of the sun and moons.
till	An unconsolidated sediment containing all sizes of fragments from clay to boulder deposited by glacial action, usually unbedded.
time scale	The division of geologic history into era, periods, and epoch accomplished through stratig-raphy and paleontology.
tonalite	Intrusive igneous rock made of plagioclase feldspar, quartz, and amphibole or biotite. May be similar to diorite but contains considerable quartz and is not as dark, and chemically has less calcium, iron and magnesium.
topographic map	"See Contour map; also a schematic drawing of prominent landforms indicated by conventionalized symbols, such as hachures or contours. "
topography	"The shape of the Earth's surface, above and below sea level; the set of landforms in a region; the distribution of elevation. "
topset bed	A horizontal sedimentary bed formed at the top of a delta and overlying the foreset beds.
trace element	An element that appears in mineral in a concentration of less than l percent (often less than 0.001 percent).
transcurrent fault	One class of vertical fault with a horizontal displacement vector that does not link two or more plate tectonic scale boundaries.
transform fault	A class of vertical fault with a horizontal displacement vector that does not link two or more plate tectonic scale boundaries.
transgression	A rise in sea level relative to the land which causes areas to be submerged and marine deposition to begin in that region.
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.
translocation	Physical or chemical migration of suspended particles or aqueous solute by moving water in a hydrochemical system or by animals and plants.
translocation crossover	Soil depth at which mass accumulation of an element by downward translocation changes from positive to zero and then to negative, thereby separating an upper soil system dominated by invasion of foreign detrital mineral from a lower, less contaminated, soil system referred to as saprolite.
transpiration	The removal of water from the ground into plants, ultimately to be evaporated into the atmosphere by them.
transportation	The movement of sediment and rocks from one location to another by water, ice, wind or gravity.
transverse dune	A dune that has its axis transverse to the prevailing winds or to a current. The upwind or upcurrent side has a gentle slope, and the downwind side lies at the angle of repose.
trap (oil)	A sedimentary or tectonic structure that impedes the upward movement of oil and gas and allows it to collect beneath the barrier.
travel time	The time required for a wave train to travel from its source to a point of observation.
travel-time curve	A curve on a graph of travel time versus distance for the arrival of seismic wave from distant events. Each type of seismic wave has its own curve.
travertine	A terrestrial deposit of limestone formed in cave and around hot spring where cooling, carbonate-saturated groundwater is exposed to the air.
trellis drainage	A system of streams in which tributaries tend to lie in parallel valleys formed in steeply dipping bed in folded belts.
trench	"A long and narrow deep trough in the sea floor; interpreted as marking the line along which a plate bends down into a subduction zone. "
triple junction	A point that is common to three plate and which must also be the meeting place of three boundary features, such as divergence zones, convergence zones, or transform fault.
tsunami	Literally harbor wave in Japanese. Tsunamis are great sea waves produced by a submarine earthquake, volcanic eruption or large landslide. Tsunamis can cause great damage due to flooding of low coastal areas.
tuff	A consolidated rock composed of pyroclastic volcanic rock made up of rock and mineral fragments in a volcanic ash matrix. Tuffs commonly are composed of much shattered volcanic rock glass--chilled magma blown into the air and then deposited. If volcanic particles fall to the ground at a very high temperature, they may fuse together, forming a welded tuff.
turam	Electromagnetic survey method in which the energizing source is a long, grounded, insulated cable or a large, rectangular, horizontal loop excited by one or more frequencies in the range of 100-1000 Hz.
turbidire	The sedimentary deposit of a turbidity current, typically showing graded bedding and sedimentary structure on the undersides of the sandstone.
turbidity current	A mass of mixed water and sediment that flows downhill along the bottom of an ocean or lake because it is denser than the surrounding water. It may reach high speeds and erode rapidly (see also Density current).
turbulent flow	A high-velocity flow in which streamlines are neither parallel nor straight but curled into small tight eddies (compare Laminar flow).
tuya	A tuya is a volcano that erupts initially beneath a glacier, melts through the ice, and develops an upper, subaerial part, which commonly consists of a flat-topped form capped by a lava flow.