Page 723 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Glossary G-4
Coordinated Universal Time (UTC) (1) The official reference time in all countries, for- merly known as Greenwich Mean Time; now measured by primary standard atomic clocks, the time calculations are collected in Paris at the International Bureau of Weights and Measures (BIPM); the legal reference for time in all countries and broadcast worldwide.
Coral (16) A simple, cylindrical marine ani- mal with a saclike body that secretes calcium carbonate to form a hard external skeleton and, cumulatively, landforms called reefs; lives symbiotically with nutrient-producing algae; presently in a worldwide state of de- cline due to bleaching (loss of algae).
Core (12) The deepest inner portion of Earth, representing one-third of its entire mass; dif- ferentiated into two zones—a solid-iron inner core surrounded by a dense, molten, fluid metallic-iron outer core.
Coriolis force (6) The apparent deflection of moving objects (wind, ocean currents, mis- siles) from travelling in a straight path, in proportion to the speed of Earth’s rotation at different latitudes. Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere; maximum at the poles and zero along the equator.
Crater (13) A circular surface depression formed by volcanism; built by accumulation, collapse, or explosion; usually located at a volcanic vent or pipe; can be at the summit or on the flank of a volcano.
Crevasse (17) A vertical crack that develops in a glacier as a result of friction between val- ley walls, or tension forces of extension on convex slopes, or compression forces on con- cave slopes.
Crust (12) Earth’s outer shell of crystalline sur- face rock, ranging from 5 to 60 km in thickness from oceanic crust to mountain ranges. Average density of continental crust is 2.7 g · cm−3, whereas oceanic crust is 3.0 g·cm−3.
Crysolic (18) A CSSC soil order that domi- nates the northern third of Canada, with per- mafrost closer to the surface and composed of mineral and organic soil deposits. Generally found north of the treeline, or in fine textured soils in subarctic forest, or in some organic soils in boreal forests.
Cryosphere (1, 17) The frozen portion of Earth’s waters, including ice sheets, ice caps and fields, glaciers, ice shelves, sea ice, and subsurface ground ice and frozen ground (per- mafrost).
Cumulonimbus (7) A towering, precipitation- producing cumulus cloud that is vertically developed across altitudes associated with other clouds; frequently associated with lightning and thunder and thus sometimes called a thunderhead.
Cumulus (7) Bright and puffy cumuliform clouds up to 2000 m in altitude.
Cyclogenesis (8) An atmospheric process that describes the birth of a midlatitude wave cyclone, usually along the polar front. Also refers to strengthening and development of a midlatitude cyclone along the eastern slope of the Rockies, other north–south mountain bar- riers, and the North American and Asian east coasts. (See Midlatitude cyclone, Polar front.)
Cyclone (6) A dynamically or thermally caused area of low atmospheric pressure with ascending and converging airflows that rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. (Compare Anticyclone; see Midlatitude cyclone, Tropical cyclone.)
Daylength (2) Duration of exposure to inso- lation, varying during the year depending on latitude; an important aspect of seasonality.
Daylight saving time (1) Time is set ahead 1 hour in the spring and set back 1 hour in the fall in the Northern Hemisphere. In Canada and the United States, time is set ahead on the second Sunday in March and set back on the first Sunday in November—except in Saskatchewan, Hawai'i, and Arizona, which exempt themselves.
Dead zone (19) Are of low-oxygen conditions and limited marine life caused by excessive nutrient inputs in coastal oceans and lakes.
Debris avalanche (14) A mass of falling and tumbling rock, debris, and soil; can be dan- gerous because of the tremendous velocities achieved by the onrushing materials.
December solstice (2) See Winter (December) solstice.
Declination (2) The latitude that receives direct overhead (perpendicular) insolation on a particular day; the subsolar point migrates annually through 47° of latitude between the Tropics of Cancer (23.5° N) and Capricorn (23.5° S).
Decomposers (19) Bacteria and fungi that digest organic debris outside their bodies and absorb and release nutrients in an ecosystem. (See Detritivore.)
Deficit (9) D in a water balance, the amount of unmet (unsatisfied) potential evapotrans- piration (PE); a natural water shortage. (See Potential evapotranspiration.)
Deflation (16) A process of wind erosion that removes and lifts individual particles, literally blowing away unconsolidated, dry, or nonco- hesive sediments.
Degradation (15) The process occurring when sediment is eroded along a stream, causing channel incision.
Delta (15) A depositional plain formed where a river enters a lake or an ocean; named after the triangular shape of the Greek letter delta, Δ.
Dendroclimatology (11) The study of past climates using tree rings. The dating of tree rings by analysis and comparison of ring widths and coloration is dendrochronology.
Denudation (14) A general term referring to all processes that cause degradation of the landscape: weathering, mass movement, ero- sion, and transport.
Deposition (15) The process whereby weath- ered, wasted, and transported sediments are laid down by air, water, and ice.
Derechos (8) Strong linear winds in excess of 26 m/sec, associated with thunderstorms and bands of showers crossing a region.
Desalination (9) In a water resources con- text, the removal of organics, debris, and sa- linity from seawater through distillation or reverse osmosis to produce potable water.
Desertification (18) The expansion of des- erts worldwide, related principally to poor agricultural practices (overgrazing and inap- propriate agricultural practices), improper soil-moisture management, erosion and sa- linization, deforestation, and the ongoing climatic change; an unwanted semiperma- nent invasion into neighboring biomes.
Desert pavement (16) On arid landscapes, a surface formed when wind deflation and sheetflow remove smaller particles, leaving re- sidual pebbles and gravels to concentrate at the surface; an alternative sediment-accumulation hypothesis explains some desert pavements; resembles a cobblestone street. (See Deflation, Sheetflow.)
Detritivore (19) Detritus feeder and decom- poser that consumes, digests, and destroys organic wastes and debris. Detritus feeders— worms, mites, termites, centipedes, snails, crabs, and even vultures, among others— consume detritus and excrete nutrients and simple inorganic compounds that fuel an ecosystem. (Compare Decomposers.)
Dew-point temperature (7) The temperature at which a given mass of air becomes satu- rated, holding all the water it can hold. Any further cooling or addition of water vapour results in active condensation.
Diagnostic subsurface horizon (18, Appendix B)
A soil horizon that originates below the epipe- don at varying depths; may be part of the A and B horizons; important in soil description as part of the Soil Taxonomy.
Differential weathering (14) The effect of different resistances in rock, coupled with variations in the intensity of physical and chemical weathering.
Diffuse radiation (4) The downward com- ponent of scattered incoming insolation from clouds and the atmosphere.
Discharge (15) The measured volume of flow in a river that passes by a given cross section of a stream in a given unit of time; expressed in cubic metre per second or cubic feet per second.
Dissolved load (15) Materials carried in chemical solution in a stream, derived from minerals such as limestone and dolomite or from soluble salts.
Downbursts (8) A powerful downdraft as- sociated with thunderstorms and bands of showers.
Downwelling current (6) An area of the sea where a convergence or accumulation of wa- ter thrusts excess water downward; occurs, for example, at the western end of the equato- rial current or along the margins of Antarc- tica. (Compare Upwelling current.)
Drainage basin (15) The basic spatial geo- morphic unit of a river system; distinguished from a neighbouring basin by ridges and high- lands that form divides, marking the limits of the catchment area of the drainage basin.
Drainage density (15) A measure of the overall operational efficiency of a drainage basin, determined by the ratio of combined channel lengths to the unit area.
Drainage pattern (15) A distinctive geomet- ric arrangement of streams in a region, deter- mined by slope, differing rock resistance to weathering and erosion, climatic and hydro- logic variability, and structural controls of the landscape.
Drawdown (9) See Cone of depression.
Drought (9) Does not have a simple water- budget definition; rather, it can occur in at least four forms: meteorological drought, agricultural drought, hydrologic drought, and/or socioeconomic drought.
Drumlin (17) A depositional landform related to glaciation that is composed of till (unstratified, unsorted) and is streamlined in the direction of continental ice movement— blunt end upstream and tapered end down- stream with a rounded summit.
Dry adiabatic rate (DAR) (7) The rate at which an unsaturated parcel of air cools (if ascending) or heats (if descending); a rate of 10 C° per 1000 m. (See Adiabatic; compare Moist adiabatic rate.)
Dune (16) A depositional feature of sand grains deposited in transient mounds, ridges,