Page 721 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Glossary G-32
groundwater flow and forms the boundary of a confined aquifer. (Compare Aquifer.)
Aquifer (9) A body of rock that conducts groundwater in usable amounts; a permeable rock layer. (Compare Aquiclude.)
Arctic Circle (2) This latitude (66.5° N) de- notes the southernmost parallel (in the North- ern Hemisphere) that experiences a 24-hour period of darkness in winter or daylight in summer.
Arctic region (17) The 10°C isotherm for July defines the Arctic region; coincides with the visible tree line—the boundary between the northern forests and tundra.
Arctic tundra (20) A biome in the northern- most portions of North America and northern Europe and Russia, featuring low, ground- level herbaceous plants as well as some woody plants. (See Alpine tundra.)
Arête (17) A sharp ridge that divides two cirque basins. Derived from “knife edge” in French, these form sawtooth and serrated ridges in glaciated mountains.
Aridisols (Appendix B) A soil order in the Soil Taxonomy; largest soil order. Typical of dry climates; low in organic matter and domi- nated by calcification and salinization.
Artesian water (9) Pressurized groundwater that rises in a well or a rock structure above the local water table; may flow out onto the ground without pumping. (See Potentiometric surface.)
Artificial levee (15) Human-built earthen embankments along river channels, often constructed on top of natural levees.
Asthenosphere (12) Region of the upper mantle just below the lithosphere; the least rigid portion of Earth’s interior and known as the plastic layer, flowing very slowly under extreme heat and pressure.
Atmosphere (1) The thin veil of gases sur- rounding Earth, which forms a protective boundary between outer space and the bio- sphere; generally considered to extend out about 480 km from Earth’s surface.
Atmosphere-Ocean General Circulation Model (AOGCM) (11) A sophisticated gen- eral circulation model that couples atmo- sphere and ocean submodels to simulate the effects of linkages between specific climate components over different time frames and at various scales.
Aurora (2) A spectacular glowing light dis- play in the ionosphere, stimulated by the in- teraction of the solar wind with principally oxygen and nitrogen gases and few other at- oms at high latitudes; called aurora borealis in the Northern Hemisphere and aurora aus- tralis in the Southern Hemisphere.
Autumnal (September) equinox (2) The time around September 22–23 when the Sun’s declination crosses the equatorial parallel (0° latitude) and all places on Earth experience days and nights of equal length. The Sun rises at the South Pole and sets at the North Pole. (Compare Vernal [March] equinox.)
Axial parallelism (2) Earth’s axis remains aligned the same throughout the year (it “re- mains parallel to itself”); thus, the axis ex- tended from the North Pole points into space always near Polaris, the North Star.
Axial tilt (2) Earth’s axis tilts 23.5° from a perpendicular to the plane of the ecliptic (plane of Earth’s orbit around the Sun).
Axis (2) An imaginary line, extending through Earth from the geographic North Pole to the geographic South Pole, around which Earth rotates.
Azores High (6) A subtropical high-pressure cell that forms in the Northern Hemisphere in the eastern Atlantic (see Bermuda High); associated with warm, clear water and large quantities of sargassum, or gulf weed, charac- teristic of the Sargasso Sea.
Bajada (15) A continuous apron of co- alesced alluvial fans, formed along the base of mountains in arid climates; presents a gently rolling surface from fan to fan. (See Alluvial fan.)
Barrier beach (16) Narrow, long, deposi- tional feature, generally composed of sand, that forms offshore roughly parallel to the coast; may appear as barrier islands and long chains of barrier beaches. (See Barrier island.)
Barrier island (16) Generally, a broadened barrier beach offshore. (See Barrier beach.)
Barrier spit (16) A depositional landform that develops when transported sand or gravel in a barrier beach or island is deposited in long ridges that are attached at one end to the main- land and partially cross the mouth of a bay.
Basalt (12) A common extrusive igneous rock, fine-grained, comprising the bulk of the ocean-floor crust, lava flows, and volcanic forms; gabbro is its intrusive form.
Base flow (9) The portion of streamflow that consists of groundwater.
Base level (15) A hypothetical level below which a stream cannot erode its valley—and thus the lowest operative level for denuda- tion processes; in an absolute sense, it is rep- resented by sea level, extending under the landscape.
Basin and Range Province (13) A region of dry climates, few permanent streams, and in- terior drainage patterns in the western United States; a faulted landscape composed of a se- quence of horsts and grabens.
Batholith (12) The largest plutonic form exposed at the surface; an irregular intrusive mass; it invades crustal rocks, cooling slowly so that large crystals develop. (See Pluton.)
Bay barrier (16) An extensive barrier spit of sand or gravel that encloses a bay, cutting it off completely from the ocean and forming a lagoon; produced by littoral drift and wave action; sometimes referred to as a baymouth bar. (See Barrier spit, Lagoon.)
Beach (16) The portion of the coastline where an accumulation of sediment is in motion.
Beach drift (16) Material, such as sand, gravel, and shells, that is moved by the long- shore current in the effective direction of the waves.
Bed load (15) Coarse materials that are dragged along the bed of a stream by traction or by the rolling and bouncing motion of sal- tation; involves particles too large to remain in suspension. (See Traction, Saltation.)
Bedrock (14) The rock of Earth’s crust that is below the soil and is basically unweath- ered; such solid crust sometimes is exposed as an outcrop.
Bergschrund (17) Forms when a crevasse or wide crack opens along the headwall of a gla- cier; most visible in summer when covering snow is gone.
Bermuda High (6) A subtropical high- pressure cell that forms in the western North Atlantic. (See Azores High.)
Biodiversity (19) A principle of ecology and biogeography: The more diverse the species population in an ecosystem (in number of species, quantity of members in each species,
and genetic content), the more risk is spread over the entire community, which results in greater overall stability, greater productivity, and increased use of nutrients, as compared to a monoculture of little or no diversity. Biogeochemical cycle (19) One of several circuits of flowing elements and materials (carbon, oxygen, nitrogen, phosphorus, wa- ter) that combine Earth’s biotic (living) and abiotic (nonliving) systems; the cycling of materials is continuous and renewed through the biosphere and the life processes. Biogeographic realm (20) One of eight re- gions of the biosphere, each representative of evolutionary core areas of related flora (plants) and fauna (animals); a broad geo- graphical classification scheme. Biogeography (19) The study of the distri- bution of plants and animals and related eco- systems; the geographical relationships with their environments over time.
Biomass (19) The total mass of living organ- isms on Earth or per unit area of a landscape; also, the weight of the living organisms in an ecosystem.
Biome (20) A large-scale, stable, terrestrial or aquatic ecosystem classified according to the predominant vegetation type and the adaptations of particular organisms to that environment.
Biosphere (1) That area where the atmo- sphere, lithosphere, and hydrosphere func- tion together to form the context within which life exists; an intricate web that connects all organisms with their physical environment. Biotic (1) Living; referring to Earth’s living system of organisms.
Bolson (13) The slope and basin area be- tween the crests of two adjacent ridges in a dry region.
Boreal forest (20) See Needleleaf forest. Brackish (16) Descriptive of seawater with a salinity of less than 35%; for example, the Baltic Sea. (Compare Brine.)
Braided stream (15) A stream that becomes a maze of interconnected channels laced with excess sediment. Braiding often occurs with a reduction of discharge that reduces a stream’s transporting ability or with an increase in sediment load.
Breaker (16) The point where a wave’s height exceeds its vertical stability and the wave breaks as it approaches the shore. Brine (16) Seawater with a salinity of more than 35%; for example, the Persian Gulf. (Compare Brackish.)
Brunisolic (18) A CSSC soil order with suf- ficiently developed horizons to distinguish it from the Regosolic order. Soils under forest cover with brownish horizons, although vari- ous colours are possible. Also, can be with mixed forest, shrubs, and grass.
Calcification (18) The illuviated (deposited) accumulation of calcium carbonate or magne- sium carbonate in the B and C soil horizons. Caldera (13) An interior sunken portion of a composite volcano’s crater; usually steep- sided and circular, sometimes containing a lake; also can be found in conjunction with shield volcanoes.
Calving (17) The process in which pieces of ice break free from the terminus of a tidewater glacier or ice sheet to form floating ice masses (icebergs) where glaciers meet an ocean, bay, or fjord.
Canadian System of Soil Classification (CSSC) (18) A soil classification system based on observable soil properties actually seen in the field; published in 1987 by the