Abyssal plain- A flat area on the deep-sea floor having a very gentle slope of less than one meter per kilometer, and consisting chiefly of graded terrigenous sediments known as turbidites (Figs. 2-3 and 2-6). A flat area on the sea floor.
Altimetry - A technique to measure the height of the sea surface from radar pulses emitted by a satellite. A tehnique to measure the height of the sea.
Andesite-A common volcanic rock found in the volcanic arcs of subduction zones; it is intermediate in composition between the granitic crust of the continents and the basaltic crust of the oceans (Table 2-2). It a common volcanic rock.
Asthenosphere-The region of the Earth''s upper mantle that, as a consequent of a small amount (<1percent) of partial melting, deforms in a plasticlike manner; it extends downward for about 250 kilometers from the base of the lithosphere (Figs. 2-1 and 3-7b). The region of the Earth' upper mantle that has 1% of partial melting.
Basalt - A dark, fine-grained igneous rock composed of minerals enriched in ferromagnesian silicates; it typifies the oceanic crust (Table 2-2). It is a dark rock that has minerals in it.
Bathymetry -The measurement of depth in the ocean in order to delineate the submarine topography (Fig. 2-2 and 2-4). The measurement of the depth in the ocean.
Bathythermograph-An instrument used to measure temperature as a function of water depth in the ocean. A instrument usrd to measure temperture .
Bimodal distribution-A frequency distribution possessing two distinct modes or maxima (Fig. 2-4). A distribution possesing two modes of maxima.
Biosphere -An external shell or envelope of the earth that includes all organic matter, both living and nonliving. A shell that includes all organic matter.
Compensation depth, isostatic- The depth in the earth or water column at which masses are balanced and pressures are equal. Water column at which masses are balanced and pressures are equal.
Continental crust -The light, buoyant granitic rock that underlies continental masses and averages about 35 kilometers in thickness (Figs. 2-4 and 2-5).
Continental margin- The drowned edges of continents consisting of the continental shelf, the continental slope, and the continental rise (Figs. 2-3 and 2-6).
Continental rise -The enormous wedge of sediment deposited at the base of the continental slope (Figs. 2-3a and 4-10).
Continental shelf - The shallow, near-horizontal sea floor extending from the coast to the upper continental slope (Figs. 2-3 and 2-7).
Continental slope -The sloping sea bottom of the continental margin that begins at a depth of about 100 to 150 meters at the shelf edge and ends at the top of the continental rise or in a deep-sea trench (Fig. 2-3).
Contour line - A line drawn on a map that connects all points of equal value (elevation, temperature, salinity, etc.) and that is used to portray the third dimension on a two-dimensional surface (Fig. IV-2 in Appendix IV).
Core -The innermost region of the earth that begins at the base of the mantle; it is composed of a very dense alloy of iron and nickel (Fig. 2-1).
Crust -The thin outermost sphere of the solid Earth consisting of either basalt (ocean crust) or granite (continental crust).
Deepsea trenches- Long, narrow, and deep topographic depressions associated with volcanic arcs that together mark a collisional zone where one lithospheric plate is overriding another (Figs. 2-3, 3-6b, and 3-11).
Density -The ratio of a mass to a unit volume specified as grams per cubic centimeter.
Echo sounding-Determining water depth by measuring the time for a pulse of sound emitted near the surface to be reflected off the bottom and return to the surface (Fig. B2-1).
Fault -A fracture in rocks or sediments along which there has been some slippage (Figs. 2-11, B3-1, B3-2, and 3-6, Table B3-1).
Fracture zone-A linear zone of highly irregular, faulted topography that is oriented perpendicular to ocean-spreading ridges (Fig. 2-3c).
Frequency distribution-
Granite -A light-colored, coarse-grained, intrusive igneous rock composed mainly of quartz and feldspar and that typifies the continental crust (Table 2-2).
Guyot -A seamount of volcanic origin with a flat top (Fig. 2-3).
Hydrosphere-The envelope of gaseous, liquid, and solid water on the earth, including oceans, lakes, groundwater, ice and snow, and water vapor (Fig. 2-1).
Igneous rock - A rock that crystallized from molten matter, either magma or lava.
Isobath -A contour line connecting all points of equal depth below the water surface.
Isostasy -The regional mass balance of rocks in the earth''s crust and uppermost mantle (Fig. 2-5).
Latitude -The angular distance north and south of the equator with the equator being 0? and the poles 90? (Fig. IV-1 in Appendix IV).
Lithosphere-The relatively cool, brittle, outer shell of the earth, some 100 kilometers thick, that includes the crust and uppermost mantle (Fig. 2-1).
Longitude --- The angular distance to the east or west of the prime meridian (0? longitude) that runs through Greenwich, England (Fig. IV-1 in Appendix IV).
Mantle -The section of the earth''s interior that extends from the base of the crust and to the top of the core and that is composed of ferromagnesian silicates (Fig. 2-1).
Mesosphere-The deep, rigid portion of the mantle that lies between the plasticlike asthenosphere and the core (Fig. 2-1).
Mid-ocean ridge-The long, continuous mountain chain found in all oceans; ocean crust is created by the process of sea-floor spreading at its crest (Figs. 2-2, 2-3, and 3-2a).
Mohorovicic discontinuity (Moho)-A compositional and density discontinuity marking the interface between the rocks of the crust and the mantle (Fig. 2-5c).
Oceanic crust -The outermost rock shell of the earth, some 5 kilometers thick, that underlies ocean basins; it is composed of basalt and sedimentary layers (Figs. 2-4 and 2-5
Oceanic ridge -The long, continuous mountain chain found in all oceans; ocean crust is created by the process of sea-floor spreading at its crest (Figs. 2-2, 2-3, and 3-2a). See mid-ocean ridge.
Passive continental margin-A subsiding continental margin situated in a nontectonic setting away from a lithospheric plate boundary. An example of a passive continental margin is the Atlantic margin of North and South America (Figs. 2-3a and 4-5d).
Relief -The difference in elevation between the highest and lowest points in an area.
Rift valley-The fault-bounded valley found along the crest of many ocean ridges; it is created by tensional stresses that accompany the process of sea-floor spreading (Figs. 2-11 and 3-2a).
Seamount -A large, individual peak, volcanic in origin, with a crest that rises more than 1,000 meters above the surrounding sea floor (Figs. 2-3 and 2-10, Table 2-1).
Shelf break-The steepening of the bottom that marks the seaward limit of the continental shelf and the beginning of the continental slope (Figs. 2-3).
SONAR -An acronym for sound navigation and ranging; an instrument used to locate objects underwater by reflecting sound waves.
Sounding -Determining the depth of water beneath a vessel (Fig. B2-1).
Submarine canyon-Deeply incised, steep-walled valley, commonly V-shaped in profile, that is cut into the rocks and sediments of the outer continental shelf and the continental slope (Fig. 2-3 and Table 2-1).
Trench -Long, narrow, and deep topographic depressions associated with volcanic arcs that together mark a collisional zone where one lithospheric plate is overriding another (Figs. 2-3, 3-6b, and 3-11). See Deep see trenches.
Vertical exaggeration-The exaggeration of the vertical scale relative to the horizontal scale in a topographic profile or section (Fig. IV-2b in Appendix IV).