Glossary - Fundamentals of the Physical Environment - page 916

Translation The movement of a shallow rock or soil mass along a failure surface or
planar discontinuity .
Transmission pore Pores in soil larger than 0·05 mm diameter which allow water to
drain away under the force of gravity.
Transport ( ation ) A process or stage in the rock cycle whereby all forms of rock and
organic debris are carried by moving water, ice or air from their point of origin to a
point of temporary or permanent deposition.
Transported soil A soil whose parent material is a transported sediment.
Trench A narrow, linear and deep depression in the sea bed caused by the subduction of
oceanic crust at a destructive plate margin.
Trench suction force The force which draws some of the upper plate down into a
subduction zone with the descending plate.
Trimline An abrupt line on a valley side separating weathered, vegetated upper slopes
from newly eroded, unvegetated lower slopes and marking the upper limit of a
contemporary or recent valley glacier.
Triple junction A three-way rift developed at the common divergent margins of three
adjacent crustal plates.
Trophic level The energy or feeding level of a particular organism in a food chain or
food web.
Trophic relationships The food web or feeding links in a community or ecosystem .
Trough A narrow, deep and steep-sided rock-walled valley typical of intense erosion by
a valley or outlet glacier .
Tsunami A seismic ocean surface wave, triggered at sea by seismovolcanic activity ,
which rises in elevation in shallow coastal waters and is capable of inflicting
considerable shoreline damage.
Turbidite The sedimentary unit formed as a turbidity current comes to rest; generally
moderately sorted, with a fining-upwards or graded sedimentary structure.
Turbidity current A turbulent, gravity-induced density current of suspended sediment,
usually in a marine or lacustrine environment, which eventually forms a turbidite .
Turbulent flow Fluid motion in which individual flow strands are confused and
multidirectional, with eddies developing within the general forward motion.
Ubac A mountain slope whose orientation shades it from the sun.
Ultramafic Said of igneous rock crystallized at high temperature and composed mostly
of magnesium-iron ( mafic ) minerals.
Unconformity A contact between two rock units indicative of a break in a continuous
sequence of rock formation; it may mark an episode of inactivity, weathering or
erosion.
Unit hydrograph The model plot of river discharge over time generated in a particular
catchment by a specified unit of precipitation.
Upwelling The rise of cold water to an ocean surface induced by divergent surface
currents.
Vadose water Water in the unsaturated zone of an aquifer .
Valley train A valley-wide, braided glacial meltwater stream and sediment system
emerging from a glacier terminus.
Vapour pressure deficit The extent of the vapour pressure gradient between subsurface
soil and a dry atmosphere.