Page 732 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

G-13 Glossary
stable if it resists displacement upward and unstable if it continues to rise.
Stationary front (8) A frontal area of contact between contrasting air masses that shows little horizontal movement; winds in oppo- site directions on either side of the front flow parallel along the front.
Steady-state equilibrium (1) The condition that occurs in a system when the rates of in- put and output are equal and the amounts of energy and stored matter are nearly constant around a stable average.
Steppe (10) A regional term referring to the vast semiarid grassland biome of Eastern Europe and Asia; the equivalent biome in North America is shortgrass prairie, and in Africa, it is the savanna. Steppe in a climatic context is considered too dry to support for- est, but too moist to be a desert.
Stomata (19) Small openings on the under- sides of leaves through which water and gas- ses pass.
Storm surge (8) A large quantity of seawater pushed inland by the strong winds associated with a tropical cyclone.
Storm track (8) Seasonally shifting path fol- lowed by a migrating low-pressure system.
Straight line winds (8) Linear winds as- sociated with thunderstorms and bands of showers that cause significant damage and crop losses. (See derechos.)
Stratified drift (17) Sediments deposited by glacial meltwater that appear sorted; a specific form of glacial drift. (Compare Till.)
Stratigraphy (12) A science that analyzes the sequence, spacing, geophysical and geo- chemical properties, and spatial distribution of rock strata.
Stratocumulus (7) A lumpy, grayish, low- level cloud, patchy with sky visible, some- times present at the end of the day.
Stratosphere (3) That portion of the homo- sphere that ranges from 20 to 50 km above Earth’s surface, with temperatures ranging from −57°C at the tropopause to 0°C at the stratopause. The functional ozonosphere is within the stratosphere.
Stratus (7) A stratiform (flat, horizontal) cloud generally below 2000 m.
Strike-slip fault (13) Horizontal movement along a fault line—that is, movement in the same direction as the fault; also known as a transcurrent fault. Such movement is de- scribed as right lateral or left lateral, depend- ing on the relative motion observed across the fault. (See Transform fault.)
Subduction zone (12) An area where two plates of crust collide and the denser oceanic crust dives beneath the less dense continen- tal plate, forming deep oceanic trenches and seismically active regions.
Sublimation (7) A process in which ice evaporates directly to water vapour or water vapour freezes to ice (deposition).
Subgroup (18) One of the five levels of hi- erarchical generalization of several levels of soil detail and grouping—a subdivision of great groups in the CSSC.
Subpolar Low (6) A region of low pressure centered approximately at 60° latitude in the North Atlantic near Iceland and in the North Pacific near the Aleutians as well as in the Southern Hemisphere. Airflow is cyclonic; it weakens in summer and strengthens in win- ter. (See Cyclone.)
Subsolar point (2) The only point receiving perpendicular insolation at a given moment—
that is, the Sun is directly overhead. (See Declination.)
Subtropical high (6) One of several dynamic high-pressure areas covering roughly the region from 20° to 35° N and S latitudes; responsible for the hot, dry areas of Earth’s arid and semiarid deserts. (See Anticyclone.) Sulfate aerosols (3) Sulfur compounds in the atmosphere, principally sulfuric acid; principal sources relate to fossil fuel combus- tion; scatter and reflect insolation.
Sulfur dioxide (SO2) (3) A colourless gas detected by its pungent odour; produced by the combustion of fossil fuels, especially coal, that contain sulfur as an impurity; can react in the atmosphere to form sulfuric acid, a component of acid deposition.
Summer (June) solstice (2) The time when the Sun’s declination is at the Tropic of Cancer, at 23.5° N latitude, June 20–21 each year. The night is 24 hours long south of the Antarctic Circle. The day is 24 hours long north of the Arctic Circle. (Compare Winter [December] solstice.)
Sunrise (2) That moment when the disk of the Sun first appears above the horizon.
Sunset (2) That moment when the disk of the Sun totally disappears below the horizon.
Sunspots (2) Magnetic disturbances on the surface of the Sun, occurring in an average 11-year cycle; related flares, prominences, and outbreaks produce surges in solar wind.
Surface creep (16) A form of eolian trans- port that involves particles too large for salta- tion; a process whereby individual grains are impacted by moving grains and slide and roll.
Surface runoff (9) Surplus water that flows across the ground surface toward stream channels when soils are saturated or when the ground is impermeable; also called over- land flow.
Surplus (9) S; the amount of moisture that exceeds potential evapotranspiration; mois- ture oversupply when soil-moisture storage is at field capacity; extra or surplus water.
Suspended load (15) Fine particles held in suspension in a stream. The finest particles are not deposited until the stream velocity nears zero.
Sustainability science (1) An emerging, integrated scientific discipline based on the concepts of sustainable development related to functioning Earth systems.
Swell (16) Regular patterns of smooth, rounded waves in open water; can range from small ripples to very large waves.
Syncline (13) A trough in folded strata, with beds that slope toward the axis of the down- fold. (Compare Anticline.)
System (1) Any ordered, interrelated set of materials or items existing separate from the environment or within a boundary; energy transformations and energy and matter stor- age and retrieval occur within a system.
occurs along narrow margins of the Pacific Northwest in North America, among other lo- cations; includes the tallest trees in the world.
Temperature (5) A measure of sensible heat energy present in the atmosphere and other media; indicates the average kinetic energy of individual molecules within a substance.
Temperature inversion (3) A reversal of the normal decrease of temperature with increas- ing altitude; can occur anywhere from ground level up to several thousand metres; functions to block atmospheric convection and thereby trap pollutants.
Terminal moraine (17) Eroded debris that is dropped at a glacier’s farthest extent.
Terrane (13) A migrating piece of Earth’s crust, dragged about by processes of mantle convection and plate tectonics. Displaced ter- ranes are distinct in their history, composi- tion, and structure from the continents that accept them.
Thermal equator (5) The isoline on an iso- thermal map that connects all points of high- est mean temperature.
Thermohaline circulation (6) Deep-ocean currents produced by differences in tempera- ture and salinity with depth; Earth’s deep currents.
Thermopause (2, 3) A zone approximately 480 km in altitude that serves conceptually as the top of the atmosphere; an altitude used for the determination of the solar constant.
Thermosphere (3) A region of the hetero- sphere extending from 80 to 480 km in alti- tude; contains the functional ionosphere layer.
Threshold (1) A moment in which a sys- tem can no longer maintain its character, so it lurches to a new operational level, which may not be compatible with previous conditions.
Thrust fault (13) A reverse fault where the fault plane forms a low angle relative to the horizontal; an overlying block moves over an underlying block.
Thunder (8) The violent expansion of sud- denly heated air, created by lightning dis- charges, which send out shock waves as an audible sonic bang.
Tide (16) A pattern of twice-daily oscil- lations in sea level produced by astronomi- cal relations among the Sun, the Moon, and Earth; experienced in varying degrees around the world. (See Neap tide, Spring tide.)
Till (17) Direct ice deposits that appear un- stratified and unsorted; a specific form of gla- cial drift. (Compare Stratified drift.)
Till plain (17) A large, relatively flat plain composed of unsorted glacial deposits behind a terminal or end moraine. Low- rolling relief and unclear drainage patterns are characteristic.
Tombolo (16) A landform created when coastal sand deposits connect the shoreline with an offshore island outcrop or sea stack.
Topographic map (Appendix A) A map that portrays physical relief through the use of elevation contour lines that connect all points at the same elevation above or below a verti- cal datum, such as mean sea level.
Topography (13) The undulations and con- figurations, including its relief, that give Earth’s surface its texture, portrayed on topographic maps.
Tornado (8) An intense, destructive cy- clonic rotation, developed in response to extremely low pressure; generally associated with mesocyclone formation.
Taiga (20)
See Needleleaf forest.
Talus slope (14) Formed by angular rock fragments that cascade down a slope along the base of a mountain; poorly sorted, cone- shaped deposits.
Tarn (17) A small mountain lake, especially one that collects in a cirque basin behind risers of rock material or in an ice-gouged depression.
Temperate rain forest (20) A major biome of lush forests at middle and high latitudes;