Page 733 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Glossary G-14
Traction (15) A type of sediment transport that drags coarser materials along the bed of a stream. (See Bed load.)
Trade winds (6) Winds from the northeast and southeast that converge in the equatorial low-pressure trough, forming the intertropi- cal convergence zone.
Transform fault (12) A type of geologic fault in rocks. An elongated zone along which faulting occurs between mid-ocean ridges; produces a relative horizontal motion with no new crust formed or consumed; strike- slip motion is either left or right lateral. (See strike-slip fault.)
Transmission (4) The passage of shortwave and longwave energy through space, the at- mosphere, or water.
Transparency (5) The quality of a medium (air, water) that allows light to easily pass through it.
Transpiration (9) The movement of water vapour out through the pores in leaves; the water is drawn by the plant roots from soil- moisture storage.
Tropic of Cancer (2) The parallel that marks the farthest north the subsolar point migrates during the year; 23.5° N latitude. (See Tropic of Capricorn, Summer [June] solstice.)
Tropic of Capricorn (2) The parallel that marks the farthest south the subsolar point migrates during the year; 23.5° S latitude. (See Tropic of Cancer, winter [December] solstice.)
Tropical cyclone (8) A cyclonic circula- tion originating in the tropics, with winds between 30 and 64 knots; characterised by closed isobars, circular organization, and heavy rains. (See Hurricane, Typhoon.)
Tropical rain forest (20) A lush biome of tall broadleaf evergreen trees and diverse plants and animals, roughly between 23.5° N and 23.5° S. The dense canopy of leaves is usually arranged in three levels.
Tropical savanna (20) A major biome con- taining large expanses of grassland inter- rupted by trees and shrubs; a transitional area between the humid rain forests and tropical seasonal forests and the drier, semiarid tropi- cal steppes and deserts.
Tropical seasonal forest and scrub (20) A variable biome on the margins of the rain forests, occupying regions of lesser and more erratic rainfall; the site of transitional communities between the rain forests and tropical grasslands.
Tropopause (3) The top zone of the tropo- sphere defined by temperature; wherever –57°C occurs.
Troposphere (3) The home of the biosphere; the lowest layer of the homosphere, contain- ing approximately 90% of the total mass of the atmosphere; extends up to the tropopause; oc- curring at an altitude of 18 km at the equator, at 13 km in the middle latitudes, and at lower altitudes near the poles.
True shape (1) A map property showing the correct configuration of coastlines; a use- ful trait of conformality for navigational and aeronautical maps, although areal relation- ships are distorted. (See Map projection; compare Equal area.)
Tsunami (16) A seismic sea wave, travel- ling at high speeds across the ocean, formed by sudden motion in the seafloor, such as a sea-floor earthquake, submarine landslide, or eruption of an undersea volcano.
Typhoon (8) A tropical cyclone with wind speeds in excess of 119 km·h−1 (65 knots)
that occurs in the western Pacific; same as a hurricane except for location. (Compare Hurricane.)
Ultisols are cultivated.
Unconfined aquifer (9) An aquifer that is not bounded by impermeable strata. It is sim- ply the zone of saturation in water-bearing rock strata with no impermeable overburden, and recharge is generally accomplished by water percolating down from above. (Com- pare to Confined aquifer.)
Undercut bank (15) In streams, a steep bank formed along the outer portion of a meander- ing stream; produced by lateral erosive action of a stream; sometimes called a cutbank. (Compare Point bar.)
Uniformitarianism (12) An assumption that physical processes active in the envi- ronment today are operating at the same pace and intensity that has characterised them throughout geologic time; proposed by Hutton and Lyell.
Upslope fog (7) Forms when moist air is forced to higher elevations along a hill or mountain and is thus cooled. (Compare Valley fog.)
Upwelling current (6) An area of the sea where cool, deep waters, which are generally nutrient-rich, rise to replace vacating water, as occurs along the west coasts of North and South America. (Compare Downwelling current.)
Urban heat island (4) An urban microcli- mate that is warmer on average than areas in the surrounding countryside because of the interaction of solar radiation and various sur- face characteristics.
Valley fog (7) The settling of cooler, more dense air in low-lying areas; produces saturat- ed conditions and fog. (Compare Upslope fog.)
Vapour pressure (7) That portion of total air pressure that results from water vapour molecules, expressed in millibars (mb). At a given dew-point temperature, the maximum capacity of the air is termed its saturation vapour pressure.
Vascular plant (19) A plant having internal fluid and material flows through its tissues; almost 270000 species exist on Earth.
Ventifact (16) A piece of rock etched and smoothed by eolian erosion—that is, abrasion by windblown particles.
Vernal (March) equinox (2) The time around March 20–21 when the Sun’s dec- lination crosses the equatorial parallel (0° latitude) and all places on Earth ex- perience days and nights of equal length. The Sun rises at the North Pole and sets at the South Pole. (Compare Autumnal [September] equinox.)
Vertisolic (18) A CSSC soil order that occurs in heavy-textured material that is high in clay content (> 60% clay), especially smectite, a shrinking and swelling clay. These soils have little development of horizons, and are marked by slickensides and usually occur under the layer of highest mixing.
Vertisols (Appendix B) A soil order in the Soil Taxonomy. Features expandable clay soils; composed of more than 30% swelling
clays. Occurs in regions that experience highly variable soil moisture balances through the seasons.
Volatile organic compounds (VOCs) (3)
Compounds, including hydrocarbons, pro- duced by the combustion of gasoline, from surface coatings, and from combustion to produce electricity; participate in the pro- duction of PAN through reactions with nitric oxides.
Volcano (13) A mountainous landform at the end of a magma conduit, which rises from below the crust and vents to the sur- face. Magma rises and collects in a magma chamber deep below, erupting effusively or explosively and forming composite, shield, or cinder-cone volcanoes.
Warm desert and semidesert (20) A desert biome caused by the presence of subtropical high-pressure cells; characterised by dry air and low precipitation.
Warm front (8) The leading edge of an ad- vancing warm air mass, which is unable to push cooler, passive air out of the way; tends to push the cooler, underlying air into a wedge shape; identified on a weather map as a line marked with semicircles pointing in the direction of frontal movement. (Compare Cold front.)
Water budget (9) A water accounting system for an area of Earth’s surface using inputs of precipitation and outputs of evapotranspira- tion (evaporation from ground surfaces and transpiration from plants) and surface runoff. Precipitation “income” balances evaporation, transpiration, and runoff “expenditures”; soil moisture storage acts as “savings” in the budget.
Water table (9) The upper surface of ground- water; that contact point between the zone of saturation and the zone of aeration in an un- confined aquifer. (See Zone of aeration, Zone of saturation.)
Water withdrawal (9) Sometimes called offstream use, the removal of water from the natural supply, after which it is used for various purposes and then is returned to the water supply.
Wave (16) An undulation of ocean water produced by the conversion of solar energy to wind energy and then to wave energy; energy produced in a generating region or a stormy area of the sea.
Wave-cut platform (16) A flat or gently sloping, tablelike bedrock surface that devel- ops in the tidal zone where wave action cuts a bench that extends from the cliff base out into the sea.
Wave cyclone (8) See Midlatitude cyclone.
Wavelength (2) A measurement of a wave; the distance between the crests of successive waves. The number of waves passing a fixed point in 1 second is called the frequency of the wavelength.
Wave refraction (16) A bending process that concentrates wave energy on headlands and disperses it in coves and bays; the long-term result is coastal straightening.
Weather (8) The short-term condition of the atmosphere, as compared to climate, which reflects long-term atmospheric conditions and extremes. Temperature, air pressure, relative humidity, wind speed and direction, day- length, and Sun angle are important measur- able elements that contribute to the weather.
Weathering (14) The processes by which surface and subsurface rocks disintegrate, or dissolve, or are broken down. Rocks at or near
Ultisols (Appendix B)
A soil order in the Soil Taxonomy. Features highly weathered forest soils, principally in the humid subtropical climatic classification. Increased weathering and exposure can degenerate an Alfisol into the reddish color and texture of these Ultisols. Fertility is quickly exhausted when