Page 720 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

G-2 Glossary
glossary
The chapter in which each term appears is boldfaced in parentheses, and is followed by a specific definition relevant to the term’s us- age in the chapter.
Aa (13) Rough, jagged, and clinkery basaltic lava with sharp edges. This texture is caused by the loss of trapped gases, a slow flow, and the development of a thick skin that cracks into the jagged surface.
Abiotic (1) Nonliving; Earth’s nonliving sys- tems of energy and materials.
Ablation (17) Loss of glacial ice through melting, sublimation, wind removal by de- flation, or the calving of blocks of ice. (See Deflation.)
Abrasion (15, 16, 17) Mechanical wearing and erosion of bedrock accomplished by the rolling and grinding of particles and rocks car- ried in a stream, removed by wind in a “sand- blasting” action, or imbedded in glacial ice.
Absorption (4) Assimilation and conversion of radiation from one form to another in a me- dium. In the process, the temperature of the absorbing surface is raised, thereby affecting the rate and wavelength of radiation from that surface.
Active layer (17) A zone of seasonally fro- zen ground that exists between the subsurface permafrost layer and the ground surface. The active layer is subject to consistent daily and seasonal freeze–thaw cycles. (See Permafrost, Periglacial.)
Actual evapotranspiration (9) AE; the ac- tual amount of evaporation and transpira- tion that occurs; derived in the water balance by subtracting the deficit (D) from potential evapotranspiration (PE).
Adiabatic (7) Pertaining to the cooling of an ascending parcel of air through expansion or the warming of a descending parcel of air through compression, without any exchange of heat between the parcel and the surround- ing environment.
Advection (4) Horizontal movement of air or water from one place to another. (Compare Convection.)
Advection fog (7) Active condensation formed when warm, moist air moves later- ally over cooler water or land surfaces, causing the lower layers of the air to be chilled to the dew-point temperature.
Aerosols (3) Small particles of dust, soot, and pollution suspended in the air.
Aggradation (15) The general building of land surface because of deposition of mate- rial; opposite of degradation. When the sedi- ment load of a stream exceeds the stream’s capacity to carry it, the stream channel becomes filled through this process.
Air (3) A simple mixture of gases (N, O, Ar, CO2, and trace gases) that is naturally odourless, colourless, tasteless, and formless, blended so thoroughly that it behaves as if it were a single gas.
Air mass (8) A distinctive, homogeneous body of air that has taken on the moisture and temperature characteristics of its source region.
Air pressure (3, 6) Pressure produced by the motion, size, and number of gas molecules in the air and exerted on surfaces in contact with the air; an average force at sea level of 1 kg · cm−3. Normal sea-level pressure, as measured by the height of a column of mer- cury (Hg), is expressed as 1013.2 millibars, 760 mm of Hg, or 29.92 inches of Hg. Air pressure can be measured with mercury or aneroid barometers (see listings for both).
Albedo (4) The reflective quality of a sur- face, expressed as the percentage of reflected insolation to incoming insolation; a function of surface color, angle of incidence, and sur- face texture.
Altocumulus (7) Middle-level, puffy clouds that occur in several forms: patchy rows, wave patterns, a “mackerel sky,” or lens-shaped “lenticular” clouds.
Andisols (Appendix B) A soil order in the Soil Taxonomy; derived from volcanic parent materials in areas of volcanic activity. A new order, created in 1990, of soils previously considered under Inceptisols and Entisols.
Anemometer (6) A device that measures wind velocity.
Aneroid barometer (6) A device that mea- sures air pressure using a partially evacuated, sealed cell. (See Air pressure.)
Angle of repose (14) The steepness of a slope that results when loose particles come to rest; an angle of balance between driving and resisting forces, ranging between 33° and 37° from a horizontal plane.
Antarctic Circle (2) This latitude (66.5° S) denotes the northernmost parallel (in the Southern Hemisphere) that experiences a 24-hour period of darkness in winter or day- light in summer.
Antarctic High (6) A consistent high- pressure region centered over Antarctica; source region for an intense polar air mass that is dry and associated with the lowest temperatures on Earth.
Antarctic region (17) The Antarctic conver- gence defines the Antarctic region in a narrow zone that extends around the continent as a boundary between colder Antarctic water and warmer water at lower latitudes.
Anthropogenic atmosphere (3) Earth’s fu- ture atmosphere, so named because humans appear to be the principal causative agent.
Anthropogenic biome (20) A recent concep- tual term for large-scale, stable ecosystems that result from ongoing human interaction with natural environments. Human modifi- cations are often linked to land-use practices such as agriculture, forestry, and urbanization.
Anticline (13) Upfolded rock strata in which layers slope downward from the axis of the fold, or central ridge. (Compare Syncline.)
Anticyclone (6) A dynamically or thermally caused area of high atmospheric pressure with descending and diverging airflows that rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemi- sphere. (Compare Cyclone.)
Aphelion (2) The point of Earth’s greatest dis- tance from the Sun in its elliptical orbit; reached on July 4 at a distance of 152 083 000 km; variable over a 100 000-year cycle. (Compare Perihelion.)
Aquiclude (9) An impermeable rock layer or body of unconsolidated materials that blocks
G-1
Aleutian Low (6)
cell.
See Subpolar low-pressure
Alfisols (Appendix B) A soil order in the Soil Taxonomy. Moderately weathered forest soils that are moist versions of Mollisols, with productivity dependent on specific patterns of moisture and temperature; rich in organics. Most wide-ranging of the soil orders.
Alluvial fan (15) Fan-shaped fluvial land- form at the mouth of a canyon; generally occurs in arid landscapes where streams are intermittent. (See bajada.)
Alluvial terraces (15) Level areas that ap- pear as topographic steps above a stream, cre- ated by the stream as it scours with renewed downcutting into its floodplain; composed of unconsolidated alluvium. (See Alluvium.)
Alluvium (15) General descriptive term for clay, silt, sand, gravel, or other unconsoli- dated rock and mineral fragments transported by running water and deposited as sorted or semisorted sediment on a floodplain, delta, or streambed.
Alpine glacier (17) A glacier confined in a mountain valley or walled basin, consisting of three subtypes: valley glacier (within a val- ley), piedmont glacier (coalesced at the base of a mountain, spreading freely over nearby lowlands), and outlet glacier (flowing out- ward from a continental glacier; compare to Continental glacier).
Alpine tundra (20) Tundra conditions at high elevation. (See Arctic tundra.)
Altitude (2) The angular distance between the horizon (a horizontal plane) and the Sun (or any point in the sky).