Page 726 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

G-7 Glossary
Hail (8) A type of precipitation formed when a raindrop is repeatedly circulated above and below the freezing level in a cloud, with each cycle freezing more moisture onto the hailstone until it becomes too heavy to stay aloft.
Hair hygrometer (7) An instrument for mea- suring relative humidity; based on the prin- ciple that human hair will change as much as 4% in length between 0% and 100% relative humidity.
Heat (4) The flow of kinetic energy from one body to another because of a temperature dif- ference between them.
Heat wave (5) A prolonged period of ab- normally high temperatures, usually, but not always, in association with humid weather. Herbivore (19) The primary consumer in a food web, which eats plant material formed by a producer (plant) that has photosynthesized organic molecules. (Compare Carnivore.) Heterosphere (3) A zone of the atmosphere above the mesopause, from 80 km to 480 km in altitude; composed of rarefied layers of oxygen atoms and nitrogen molecules; includes the ionosphere.
Histosols (Appendix B) A soil order in the Soil Taxonomy. Formed from thick accumula- tions of organic matter, such as beds of former lakes, bogs, and layers of peat.
Homosphere (3) A zone of the atmosphere from Earth’s surface up to 80 km, composed of an even mixture of gases, including nitro- gen, oxygen, argon, carbon dioxide, and trace gases.
all sides.
Horst (13) Upward-faulted blocks produced by pairs or groups of faults; characteristic of the mountain ranges of the interior of the western United States. (See Graben, Basin and Range Province.)
Hot spot (12) An individual point of upwell- ing material originating in the asthenosphere, or deeper in the mantle; tends to remain fixed relative to migrating plates; some 100 are iden- tified worldwide, exemplified by Yellowstone National Park, Hawai’i, and Iceland. Human–Earth relationships (1) One of the oldest themes of geography (the human–land tradition); includes the spatial analysis of settlement patterns, resource utilization and exploitation, hazard perception and plan- ning, and the impact of environmental modi- fication and artificial landscape creation. Humidity (7) Water vapour content of the air. The capacity of the air for water vapour is mostly a function of the temperature of the air and the water vapour.
Humus (18) A mixture of organic debris in the soil worked by consumers and decompos- ers in the humification process; characteris- tically formed from plant and animal litter deposited at the surface.
Hurricane (8) A tropical cyclone that is fully organized and intensified in inward-spiraling rainbands; ranges from 160 to 960 km in diameter, with wind speeds in excess of 119 km·h−1 (65 knots); a name used spe- cifically in the Atlantic and eastern Pacific. (Compare Typhoon.)
Hydration (14) A chemical weathering process involving water that is added to a mineral, which initiates swelling and stress within the rock, mechanically forcing grains apart as the constituents expand. (Compare Hydrolysis.)
Hydraulic action (15) The erosive work ac- complished by the turbulence of water; causes a squeezing and releasing action in joints in bedrock; capable of prying and lifting rocks. Hydrograph (15) A graph of stream dis- charge (in m3·s−1) over a period of time (minutes, hours, days, years) at a specific place on a stream. The relationship between stream discharge and precipitation input is illustrated on the graph.
Hydrologic cycle (9) A simplified model of the flow of water, ice, and water vapour from place to place. Water flows through the atmo- sphere and across the land, where it is stored as ice and as groundwater. Solar energy em- powers the cycle.
Hydrology (15) The science of water, includ- ing its global circulation, distribution, and properties—specifically water at and below Earth’s surface.
Hydrolysis (14) A chemical weathering pro- cess in which minerals chemically combine with water; a decomposition process that causes silicate minerals in rocks to break down and become altered. (Compare Hydration.) Hydropower (9) Electricity generated using the energy of moving water, usually flowing downhill through the turbines at a dam; also called hydroelectric power.
Hydrosphere (1) An abiotic open system that includes all of Earth’s water. Hygroscopic water (9) That portion of soil moisture that is so tightly bound to each soil particle that it is unavailable to plant roots; the water, along with some bound capillary water, that is left in the soil after the wilting point is reached. (See Wilting point.)
Ice age (17) A cold episode, with accompa- nying alpine and continental ice accumula- tions, that has repeated roughly every 200 to 300 million years since the late Precambrian Era (1.25 billion years ago); includes the most recent episode during the Pleistocene Ice Age, which began 1.65 million years ago.
Ice cap (17) A large, dome-shaped glacier, less extensive than an ice sheet although it buries mountain peaks and the local land- scape; generally, less than 50 000 km2.
Ice-crystal fog (7) A type of fog that devel- ops at very low temperatures in a continental arctic air mass. Visibility is seriously limited when the air becomes full of ice crystals that have formed by sublimation.
Ice field (17) The least extensive form of a glacier, with mountain ridges and peaks vis- ible above the ice; less than an ice cap or ice sheet.
Icelandic Low (6) See Subpolar low- pressure cell.
Ice sheet (17) A continuous mass of uncon- fined ice, covering at least 50 000 km2. The bulk of glacial ice on Earth covers Antarctica and Greenland in two ice sheets. (Compare Alpine glacier.)
Igneous rock (12) One of the basic rock types; it has solidified and crystallized from a hot molten state (either magma or lava). (Com- pare Metamorphic rock, Sedimentary rock.)
Illuviation (18) The downward movement and deposition of finer particles and minerals from the upper horizon of the soil; a deposi- tional process. Deposition usually is in the B horizon, where accumulations of clays, alumi- num, carbonates, iron, and some humus occur. (Compare Eluviation; see Calcification.)
Inceptisols (Appendix B) A soil order in the Soil Taxonomy. Weakly developed soils that
are inherently infertile; usually, young soils that are weakly developed, although they are more developed than Entisols.
Industrial smog (3) Air pollution associated with coal-burning industries; it may contain sulfur oxides, particulates, carbon dioxide, and exotics.
Infiltration (9) Water access to subsurface regions of soil moisture storage through pen- etration of the soil surface.
Insolation (2) Solar radiation that is incom- ing to Earth systems.
Interception (9) A delay in the fall of pre- cipitation toward Earth’s surface caused by vegetation or other ground cover.
Internal drainage (15) In regions where rivers do not flow into the ocean, the out- flow is through evaporation or subsurface gravitational flow. Portions of Africa, Asia, Australia, and the western United States have such drainage.
International Date Line (IDL) (1) The 180° meridian, an important corollary to the prime meridian on the opposite side of the planet; established by an 1884 treaty to mark the place where each day officially begins.
Intertropical convergence zone (ITCZ) (6)
See Equatorial low-pressure trough.
Intrusive igneous rock (12) A rock that so- lidifies and crystallizes from a molten state as it intrudes into crustal rocks, cooling and hardening below the surface, such as granite.
Invasive species (20) Species that are brought, or introduced, from elsewhere by humans, either accidentally or intentionally. These non-native species are also known as exotic species or alien species.
Ionosphere (3) A layer in the atmosphere above 80 km (50 mi) where gamma, X-ray, and some ultraviolet radiation is absorbed and converted into longer wavelengths and where the solar wind stimulates the auroras.
Island biogeography (20) Island communi- ties are special places for study because of their spatial isolation and the relatively small number of species present. Islands resemble natural experiments because the impact of individual factors, such as civilization, can be more easily assessed on islands than over larger continental areas.
Isobar (6) An isoline connecting all points of equal atmospheric pressure.
Isostasy (12) A state of equilibrium in Earth’s crust formed by the interplay between portions of the less-dense lithosphere and the more-dense asthenosphere and the prin- ciple of buoyancy. The crust depresses under weight and recovers with its removal—for example, with the melting of glacial ice. The uplift is known as isostatic rebound.
Isotherm (5) An isoline connecting all points of equal temperature.
Isotope analysis (11) A technique for long- term climatic reconstruction that uses the atomic structure of chemical elements, spe- cifically the relative amounts of their iso- topes, to identify the chemical composition of past oceans and ice masses.
Jet contrails (4) Condensation trails pro- duced by aircraft exhaust, particulates, and water vapour can form high cirrus clouds, sometimes called false cirrus clouds.
Jet stream (6) The most prominent movement in upper-level westerly wind flows; irregular, concentrated, sinuous bands of geostrophic wind, travelling at 300 km · h−1.
Horn (17)
A pyramidal, sharp-pointed peak that results when several cirque glaciers gouge an individual mountain summit from