Page 729 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Glossary G-10
Occluded front (8) In a cyclonic circulation, the overrunning of a surface warm front by a cold front and the subsequent lifting of the warm air wedge off the ground; initial pre- cipitation is moderate to heavy.
Ocean basin (13) The physical container (a depression in the lithosphere) holding an ocean.
Omnivore (19) A consumer that feeds on both producers (plants) and consumers (meat)—a role occupied by humans, among other ani- mals. (Compare Consumer, Producer.)
Open system (1) A system with inputs and outputs crossing back and forth between the system and the surrounding environment. Earth is an open system in terms of energy. (Compare Closed system.)
Order (18) The principal classification of the five levels of hierarchical generalization of several levels of soil detail and grouping— consisting of the ten soil orders in the CSSC. Organic (18) A CSSC soil order with peat, bog, and muck soils, largely composed of organ- ic material. Most are water-saturated for pro- longed periods. Are widespread in association with poorly to very poorly drained depressions, although Folisols are found under upland forest environments. Exceed 17% organic carbon and 30% organic matter overall.
Orogenesis (13) The process of mountain building that occurs when large-scale com- pression leads to deformation and uplift of the crust; literally, the birth of mountains. Orographic lifting (8) The uplift of a migrat- ing air mass as it is forced to move upward over a mountain range—a topographic barrier. The lifted air cools adiabatically as it moves upslope; clouds may form and produce in- creased precipitation.
Outgassing (9) The release of trapped gases from rocks, forced out through cracks, fis- sures, and volcanoes from within Earth; the terrestrial source of Earth’s water.
Outwash plain (17) Area of glacial stream deposits of stratified drift with meltwater-fed, braided, and overloaded streams; occurs be- yond a glacier’s morainal deposits.
Overland flow (9) Surplus water that flows across the land surface toward stream chan- nels. Together with precipitation and subsur- face flows, it constitutes the total runoff from an area.
Oxbow lake (15) A lake that was formerly part of the channel of a meandering stream; isolated when a stream eroded its outer bank, forming a cutoff through the neck of the loop- ing meander (see Meandering stream). In Australia, known as a billabong (the Aborigi- nal word for “dead river”).
Oxidation (14) A chemical weathering process in which oxygen dissolved in water oxidizes (combines with) certain metallic el- ements to form oxides; most familiar is the “rusting” of iron in a rock or soil (Ultisols, Oxisols), which produces a reddish-brown stain of iron oxide.
Oxisols (Appendix B) A soil order in the Soil Taxonomy. Tropical soils that are old, deeply developed, and lacking in horizons wherever well drained; heavily weathered, low in cation-exchange capacity, and low in fertility.
Ozone layer (3) See Ozonosphere. Ozonosphere (3) A layer of ozone occupy- ing the full extent of the stratosphere (20 to 50 km above the surface); the region of the atmosphere where ultraviolet wavelengths of insolation are extensively absorbed and con- verted into heat.
Pacific High (6) A high-pressure cell that dominates the Pacific in July, retreating southward in the Northern Hemisphere in January; also known as the Hawaiian high.
Pahoehoe (13) Basaltic lava that is more fluid than aa. Pahoehoe forms a thin crust that forms folds and appears “ropy,” like coiled, twisted rope.
Paleoclimatology (11) The science that stud- ies the climates, and the causes of variations in climate, of past ages, throughout historic and geologic time.
Paleolake (17) An ancient lake, such as Lake Bonneville or Lake Lahonton, associated with former wet periods when the lake basins were filled to higher levels than today.
PAN (3) See Peroxyacetyl nitrate.
Pangaea (12) The supercontinent formed by the collision of all continental masses approx- imately 225 million years ago; named in the continental drift theory by Wegener in 1912. (See Plate tectonics.)
Parallel (1) A line, parallel to the equator, that designates an angle of latitude. (See Latitude.)
Parent material (14) The unconsolidated material, from both organic and mineral sources, that is the basis of soil development.
Particulate matter (PM) (3) Dust, dirt, soot, salt, sulfate aerosols, fugitive natural par- ticles, or other material particles suspended in air.
Paternoster lake (17) One of a series of small, circular, stair-stepped lakes formed in individ- ual rock basins aligned down the course of a glaciated valley; named because they look like a string of rosary (religious) beads.
Patterned ground (17) Areas in the perigla- cial environment where freezing and thaw- ing of the ground create polygonal forms of arranged rocks at the surface; can be circles, polygons, stripes, nets, and steps.
Pedogenic regime (18) A specific soil-forming process keyed to a specific climatic regime: laterization, calcification, salinization, and podsolization, among others; not the basis for soil classification in the Soil Taxonomy.
Pedon (18) A soil profile extending from the surface to the lowest extent of plant roots or to the depth where regolith or bedrock is en- countered; imagined as a hexagonal column; the basic soil sampling unit.
Percolation (9) The process by which wa- ter permeates the soil or porous rock into the subsurface environment.
Periglacial (17) Cold-climate processes, landforms, and topographic features along the margins of glaciers, past and present; peri- glacial characteristics exist on more than 20% of Earth’s land surface; includes permafrost, frost action, and ground ice.
Perihelion (2) The point of Earth’s closest ap- proach to the Sun in its elliptical orbit, reached on January 3 at a distance of 147 255 000 km; variable over a 100 000-year cycle. (Compare Aphelion.)
Permafrost (17) Forms when soil or rock temperatures remain below 0°C for at least 2 years in areas considered periglacial; cri- terion is based on temperature and not on whether water is present. (See Periglacial.)
Permeability (9) The ability of water to flow through soil or rock; a function of the texture and structure of the medium.
Peroxyacetyl nitrate (PANs) (3) A pollutant formed from photochemical reactions involv- ing nitric oxide (NO) and volatile organic compounds (VOCs). PAN produces no known
human health effect, but is particularly dam- aging to plants.
Phase change (7) The change in phase, or state, among ice, water, and water vapour; involves the absorption or release of latent heat. (See Latent heat.)
Photochemical smog (3) Air pollution pro- duced by the interaction of ultraviolet light, nitrogen dioxide, and hydrocarbons; produces ozone and PAN through a series of complex photochemical reactions. Automobiles are the major source of the contributive gases.
Photogrammetry (1) The science of obtain- ing accurate measurements from aerial pho- tos and remote sensing; used to create and to improve surface maps.
Photosynthesis (19) The process by which plants produce their own food from carbon dioxide and water, powered by solar energy. The joining of carbon dioxide and hydro- gen in plants, under the influence of certain wavelengths of visible light; releases oxygen and produces energy-rich organic material, sugars, and starches. (Compare Respiration.)
Physical geography (1) The science con- cerned with the spatial aspects and interac- tions of the physical elements and process sys- tems that make up the environment: energy, air, water, weather, climate, landforms, soils, animals, plants, microorganisms, and Earth.
Physical weathering (14) The breaking up and disintegrating of rock without any chem- ical alteration; sometimes referred to as me- chanical or fragmentation weathering.
Pioneer community (19) The initial plant community in an area; usually is found on new surfaces or those that have been stripped of life, as in beginning primary succession, and includes lichens, mosses, and ferns grow- ing on bare rock.
Place (1) A major theme in geography, fo- cused on the tangible and intangible charac- teristics that make each location unique; no two places on Earth are alike.
Plane of the ecliptic (2) A plane (flat surface) intersecting all the points of Earth’s orbit.
Planetesimal hypothesis (2) Proposes a pro- cess by which early protoplanets formed from the condensing masses of a nebular cloud of dust, gas, and icy comets; a formation pro- cess now being observed in other parts of the galaxy.
Planimetric map (Appendix A) A basic map showing the horizontal position of boundar- ies; land-use activities; and political, eco- nomic, and social outlines.
Plateau basalt (13) An accumulation of horizontal flows formed when lava spreads out from elongated fissures onto the surface in extensive sheets; associated with effusive eruptions; also known as flood basalts. (See Basalt.)
Plate tectonics (12) The conceptual model and theory that encompass continental drift, sea-floor spreading, and related aspects of crustal movement; accepted as the founda- tion of crustal tectonic processes. (See Con- tinental drift.)
Playa (15) An area of salt crust left behind by evaporation on a desert floor, usually in the middle of a desert or semiarid bolson or valley; intermittently wet and dry.
Plough winds (8) Linear winds associated with thunderstorms and bands of showers that cause significant damage and crop losses. (See derechos.)
Pluton (12) A mass of intrusive igneous rock that has cooled slowly in the crust; forms in