Page 730 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

G-11 Glossary
any size or shape. The largest partially ex- posed pluton is a batholith. (See Batholith.) Podsolization (18) A pedogenic process in cool, moist climates; forms a highly leached soil with strong surface acidity because of humus from acid-rich trees.
Podzolic (18) A CSSC soil order of the conif- erous forests and sometimes heath; leaching of overlying horizons occurs in moist, cool to cold climates.
Point bar (15) In a stream, the inner portion of a meander, where sediment fill is redepos- ited. (Compare Undercut bank.)
Polar easterlies (6) Variable, weak, cold, and dry winds moving away from the polar region; an anticyclonic circulation.
Polar desert (20) A type of desert biome found at higher latitudes than cold deserts, occurring mainly in the very cold, dry cli- mates of Greenland and Antartica.
Polar front (6) A significant zone of con- trast between cold and warm air masses; roughly situated between 50° and 60° N and S latitude.
Polar High (6) Weak, anticyclonic, ther- mally produced pressure systems positioned roughly over each pole; that over the South Pole is the region of the lowest temperatures on Earth. (See Antarctic High.)
Pollutants (3) Natural or human-caused gases, particles, and other substances in the troposphere that accumulate in amounts harmful to humans or to the environment. Positive feedback (1) Feedback that ampli- fies or encourages responses in a system. (Com- pare Negative feedback; see Feedback loop.) Potential evapotranspiration (9) PE; the amount of moisture that would evaporate and transpire if adequate moisture were available; it is the amount lost under optimum moisture conditions, the moisture demand. (Compare Actual evapotranspiration.)
Potentiometric surface (9) A pressure level in a confined aquifer, defined by the level to which water rises in wells; caused by the fact that the water in a confined aquifer is under the pressure of its own weight; also known as a piezometric surface. This surface can extend above the surface of the land, causing water to rise above the water table in wells in confined aquifers. (See Artesian water.) Precipitation (9) Rain, snow, sleet, and hail— the moisture supply; called P in the water balance.
Pressure gradient force (6) Causes air to move from an area of higher barometric pres- sure to an area of lower barometric pressure due to the pressure difference.
Primary succession (19) Succession that oc- curs among plant species in an area of new surfaces created by mass movement of land, cooled lava flows and volcanic eruption land- scapes, or surface mining and clear-cut log- ging scars; exposed by retreating glaciers, or made up of sand dunes, with no trace of a former community.
Prime meridian (1) An arbitrary meridian designated as 0° longitude, the point from which longitudes are measured east or west; established at Greenwich, England, by inter- national agreement in an 1884 treaty.
Process (1) A set of actions and changes that occur in some special order; analysis of process- es is central to modern geographic synthesis. Producer (19) Organism (plant) in an eco- system that uses carbon dioxide as its sole source of carbon, which it chemically fixes through photosynthesis to provide its own
nourishment; also called an autotroph. (Com- pare Consumer.)
Proxy method (11) Information about past environments that represent changes in cli- mate, such as isotope analysis or tree ring dating; also called a climate proxy.
Pyroclastic (13) An explosively ejected rock fragment launched by a volcanic eruption; sometimes described by the more general term tephra.
Radiation fog (7) Formed by radiative cool- ing of a land surface, especially on clear nights in areas of moist ground; occurs when the air layer directly above the surface is chilled to the dew-point temperature, thereby producing saturated conditions.
Radiative forcing (11) The amount by which some perturbation causes Earth’s energy bal- ance to deviate from zero; a positive forcing indicates a warming condition, a negative forcing indicates cooling; also called climate forcing.
Radioactive isotope (11) An unstable iso- tope that decays, or breaks down, into a different element, emitting radiation in the process. The unstable isotope carbon-14 has a constant rate of decay known as a half-life that can be used to date plant material in a technique called radiocarbon dating.
Rain gauge (9) A weather instrument; a standardized device that captures and mea- sures rainfall.
Rain shadow (8) The area on the leeward slope of a mountain range where precipita- tion receipt is greatly reduced compared to the windward slope on the other side. (See Orographic lifting.)
Reflection (4) The portion of arriving insola- tion that is returned directly to space without being absorbed and converted into heat and without performing any work. (See Albedo.)
Refraction (4) The bending effect on electro- magnetic waves that occurs when insolation enters the atmosphere or another medium; the same process disperses the component colors of the light passing through a crystal or prism.
Region (1) A geographic theme that focuses on areas that display unity and internal ho- mogeneity of traits; includes the study of how a region forms, evolves, and interrelates with other regions.
Regosolic (18) A CSSC soil order with weak- ly developed limited soils, the result of any number of factors: young materials; fresh allu- vial deposits; material instability; mass-wasted slopes; or dry, cold climatic conditions.
Regolith (14) Partially weathered rock over- lying bedrock, whether residual or transported.
Relative humidity (7) The ratio of water vapour actually in the air (content) to the max- imum water vapour possible in air (capacity) at that temperature; expressed as a percent- age. (Compare Vapour pressure, Specific humidity.)
Relief (13) Elevation differences in a local landscape; an expression of local height dif- ferences of landforms.
Remote sensing (1) Information acquired from a distance, without physical contact with the subject—for example, photography, orbital imagery, and radar.
Respiration (19) The process by which plants oxidize carbohydrates to derive energy for their operations; essentially, the reverse of the photosynthetic process; releases carbon
dioxide, water, and heat energy into the envi- ronment. (Compare Photosynthesis.)
Reverse fault (13) Compressional forces pro- duce strain that breaks a rock so that one side moves upward relative to the other side; also called a thrust fault. (Compare Normal fault.)
Revolution (2) The annual orbital move- ment of Earth about the Sun; determines the length of the year and the seasons.
Rhumb line (1) A line of constant compass direction, or constant bearing, that crosses successive meridians at the same angle; appears as a straight line only on the Merca- tor projection.
Richter scale (13) An open-ended, logarith- mic scale that estimates earthquake amplitude magnitude; designed by Charles Richter in 1935; now replaced by the moment magnitude scale. (See Moment magnitude [M] scale.)
Rime fog (7) A fog that consists of super- cooled water droplets that turn into rime frost on contact with freezing objects.
Ring of Fire (13) See Circum-Pacific belt. Robinson projection (Appendix A) A com-
promise (neither equal area nor true shape) oval projection developed in 1963 by Arthur Robinson.
Roche moutonnée (17) A glacial erosion feature; an asymmetrical hill of exposed bedrock; displays a gently sloping upstream side that has been smoothed and polished by a glacier and an abrupt, steep downstream side.
Rock (12) An assemblage of minerals bound together, or sometimes a mass of a single mineral.
Rock cycle (12) A model representing the interrelationships among the three rock- forming processes: igneous, sedimentary, and metamorphic; shows how each can be trans- formed into another rock type.
Rockfall (14) Free-falling movement of de- bris from a cliff or steep slope, generally fall- ing straight or bounding downslope.
Rossby wave (6) An undulating horizontal motion in the upper-air westerly circulation at middle and high latitudes.
Rotation (2) The turning of Earth on its axis, averaging about 24 hours in duration; deter- mines day–night relation; counterclockwise when viewed from above the North Pole and from west to east, or eastward, when viewed from above the equator.
Salinity (16) The concentration of natural elements and compounds dissolved in solu- tion, as solutes; measured by weight in parts per thousand (‰) in seawater.
Salinization (18) A pedogenic process that results from high potential evapotranspira- tion rates in deserts and semiarid regions. Soil water is drawn to surface horizons, and dissolved salts are deposited as the water evaporates.
Saltation (15) The transport of sand grains (usually larger than 0.2 mm) by stream or wind, bouncing the grains along the ground in asymmetrical paths.
Salt marsh (16) A wetland ecosystem char- acteristic of latitudes poleward of the 30th parallel. (Compare Mangrove swamp.)
Sand sea (16) An extensive area of sand and dunes; characteristic of Earth’s erg deserts. (Compare Erg desert.)
Saturation (7) State of air that is holding all the water vapour that it can hold at a given tem- perature, known as the dew-point temperature.