Glossary Database

Select a Letter to view the associated terms.

 Glossary Term: 


 B horizon  The solid zone of accumulation underlying the A horizon of a soil profile. Some of the material dissolved by leaching in the A horizon is deposited in the B horizon.
 Bachelor  an unmated male
 Backarc basin  The area behind a subduction-related volcanic arc where folds and faults form. Most oceanic backarcs are extending.
 Backswamp  The marshy area of a flood plain at some distance beyond and lower than the natural levees that confine the river.
 Backwash  The return sheet flow down a beach after a wave is spent.
 Bacteria  Microorganisms which have no chlorophyll and multiply by simple division. Some cause disease but others are beneficial.
 Badlands  An area nearly devoid of vegetation and dissected by stream erosion into an intricate system of closely spaced, narrow ravines.
 Bajada  The surface of a system of coalesced alluvial fans.
 Balancers  Lateral appendages on the heads of some larval salamanders (Morris 1992).
 Bar  An offshore, submerged, elongate ridge of sand or gravel built on the sea floor by waves and currents.
 barbs  Small spine-like projections found on the anterior or posterior surface of the pectoral spines of catfishes, and on the posterior edges of the dorsal and anal spines of carp.
 Barchan dune  A crescent-shaped dune, the tips or horns of which point downwind. Barchan dunes form in desert areas where sand is scarce.
 barging  Artificial transportation of young salmon downstream in barges, in areas where currents are slowed behind dams and the fish cannot move downstream quickly enough.
 Barrier island  An elongate island of sand or gravel formed parallel to a coast.
 Barrier reef axi  elongate coral reef that trends parallel to the shore of an island or a continent, separated from it by a lagoon.
 Basalt  A dark-colored, fine-grained, mafic volcanic rock composed of plagioclase (over 50%) and pyroxene. Olivine may or may not be present.
 Base level  The level below which a stream cannot effectively erode. Sea level is the ultimate base level, but lakes form temporary base levels for inland drainage systems.
 Basement complex  A series of igneous and metamorphic rocks lying beneath the oldest stratified rocks of a region. In shields, the basement complex is exposed over large areas.
 Basin  1. structural geology. A circular or elliptical downwarp. After erosion, the youngest beds are exposed in the central part of the structure. 2. Topography. A depression into which the surrounding area drains.
 Basin and Range  A physiographic province of North America where the crust is extending, characterized by tilted fault block mountain ranges and valleys, located in the western United States between the Rocky Mountains and the coast ranges.
 Basking  Resting in the direct rays of the sun (Peters 1964).
 Batholith  A large body of intrusive igneous rock exposed over an area of at least 100 km2.
 Bathymetry  The measurement of ocean depths and mapping of the topography of the ocean floor.
 Bauxite  A mixture of various amorphous or crystalline hydrous aluminum oxides and aluminum hydroxides, commonly formed by intense chemical weathering in tropical and subtropical regions. Bauxite is the principal ore of aluminum.
 Bay  A wide, curving recess or inlet between two capes or headlands.
 Baymouth bar  A narrow, usually submerged ridge of sand or gravel deposited across the mouth of a bay by longshore drift. Baymouth bars commonly are formed by extension of spits along embayed coasts.
 Beach  A deposit of wave-washed sediment along a coast between the landward limit of wave action and the outermost breakers.
 Bed  A layer of sediment 1 cm or more in thickness.
 Bed load  Material transported along the bottom of a stream by rolling or sliding, in contrast to material carried in suspension or in solution.
 Bedding plane  A surface separating layers of sedimentary rock.
 Bedrock  The continuous solid rock that underlies the regolith everywhere and is exposed locally at the surface. An exposure of bedrock is called an outcrop.
 belly  The underside of the fish's body.
 Benioff zone  A zone of earthquakes that dips away from a deep-sea trench and slopes beneath the adjacent continent or island arc.
 Berm  A nearly horizontal portion of a beach or backshore formed by storm waves. Some beaches have no berms; others have several.
 Bib  a patch of colored feathers under the chin of a bird
 Biennial  Requiring two years to complete development and life cycle.
 Biennial reproduction  Having a two-year reproductive cycle (Morris 1992).
 Bimodal foraging  having two modes of foraging
 Binocular vision  having to do with or the use of both eye simultaneously (Morris 1992).
 Biosphere  The totality of life on or near Earth's surface.
 Biotite  A common rock forming mineral of the mica group.
 Biotite (black mica)  An important mafic silicate with silicon-oxygen tetrahedra arranged in sheets.
 Bird-foot delta  A delta with distributaries extending seaward and, in map view, resembling the claws of a bird. Example: the Mississippi Delta.
 Block faulting  A type of normal faulting in which segments of the crust are broken and displaced to different elevations and orientations.
 block lava  Basaltic lava in the form of a chaotic assemplage of angular blocks.
 Blowout  A dune shaped like a parabola with the concave side toward the wind. Commonly formed along shorelines. Same as a parabolic dune.
 Blueschist  A fine-grained schistose rock characterized by high-pressure, low-temperature mineral assemblages, and typically containing the blue amphibole glaucophane.
 Boreal  Of or relating to the north (Morris 1992).
 Botulism  Food poisoning by the neurotoxin botulin, characterized by vomiting, abdominal pain, difficulty of vision, central nervous systems, disturbances of secretion, dyspepsia, a barking cough, and ptsosis (Morris 1992).
 Boulder  A rock fragment with a diameter of more than 256 mm (about the size of a volleyball). A boulder is one size larger than a cobble.
 Brachiopod  Any marine invertebrate belonging to the phylum Brachiopoda, characterized by two bilaterally symmetrical valves.
 Bracketed intrusion  An intrusive rock that was once exposed at the surface by erosion and was subsequently covered by younger sediment. The relative age of the intrusion thus falls between, or is bracketed by, the ages of the younger and older sedimentary deposits.
 Brackish  Describing water that is slightly salty; water whose salinity is between that of normal fresh water and normal sea water (Morris 1992).
 Bract  A specialized plant leaf which is most commonly located directly beneath a flower.
 Bracts  1. a small modified leaf with a relative undeveloped blade, in the axil of which grows an inflorescence or flower. 2. a leaf or leaflike structure associated with a sporangium (Morris 1992).
 Braided stream  A stream with a complex of converging and diverging channels separated by bars or islands. Braided streams form where more sediment is available than can be removed by the discharge of the stream.
 branchiostegal rays  The rays on under side of head which support the gill membrane.
 Breaker  A collapsing water wave.
 Breccia  1. A general term for sediment consisting of angular fragments in a matrix of finer particles. Examples: sedimentary breccias, volcanic breccias, fault breccias, impact breccias. 2. A coarse-grained clastic rock, consisting of angular fragments held together by a mineral cement of fine grained matrix
 Breccia  a coarse-grained clastic rock, consisting of angular fragments held together by a mineral cement of fine grained matrix
 Brittle  Easily broken or fractured in contrast to plastic flow. Contrasts with ductile.
 Brood  1.)A single generation of butterflies, all of which fly during the same time period. 2.)The offspring of animals, usually a number of young that are produced or hatched at one time (Morris 1992)
 Browse  1. to eat; nibble at; eat from. 2. to graze; feed on; pasture on (Stein 1966). Browser
 Bubonic Plague  The most common form of plague, characterized by an abrupt onset of fever, chills, weakness, and headache followed by pain, tenderness, and buboes associated with a marked hemorrahagic tendency, the development of of disseminated coagulation, necrotic purpura, and extensive symmetrical gangrene; severe complications include pneumonia and septicemia. The notorious Black Plague that devastated the population of Europe and Asia in the 1300s was a form of bubonic plague (Morris 1992).
 Buff  Yellowish-brown; medium or dark tan (Stein 1966).
 Buoyant  Having the ability or tendency to float.
 Butte  A somewhat isolated hill, usually capped with a resistant layer of rock and bordered by talus. A butte is an erosional remnant of a formerly more extensive slope.