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B Horizon - 

Soil horizon normally found below the A horizon and above the C horizon. This layer is characterized by the following features:
(1) Enrichment of clay because of illuviation from the A horizon.
(2) Enrichment of iron and aluminum oxides because of illuviation of these materials from the A horizon. In some cases the precipitation of iron can cause the development of a hardpan.
(3) Accumulation of calcium carbonate, calcium sulfate, and other salts.
(4) Higher bulk density because of the illuvial deposition of clay particles.

Background Extinction - 

Normal extinction of species that occurs as a result of changes in local environmental conditions. Also see mass extinction.

Backscattering -  Portion of solar radiation directed back into space as a result of particle scattering in the atmosphere.
Backshore - 

Area behind the shore. This coastal feature is located between the beach berm and the backshore slope.

Backshore slope - 

Sloping bank landward of the shore. This coastal feature is composed of relatively non-mobile sediments.

Backswamp - 

Marshy low lying area in a stream's floodplain. Commonly found behind levees.

Backwash - 

The return water flow of swash. This sheet of water flows back to ocean because of gravity.

Bacteria - 

Simple single celled prokaryotic organisms. Many different species of bacteria exist. Some species of bacteria can be pathogenic causing disease in larger more complex organisms. Many species of bacteria play a major role in the cycling of nutrients in ecosystems through aerobic and anaerobic decomposition. Finally, some species form symbiotic relationships with more complex organisms and help these life forms survive in the environment by fixing atmospheric nitrogen.

Badlands - 

(1) Term used to describe a part of South Dakota.
(2) Term used to describe a semi-arid landscape that has been influenced by heavy fluvial erosion. Characterized by deep ravines and gullies, shape ridges, and a generally barren surface.

Bajada - 

Consecutive series of alluvial fans forming along the edge of a linear mountain range. Surface of this feature undulates in a rolling fashion as one moves from the center of one alluvial fan to another. Normally occurs in arid climates.

Bank-Caving - 

Collapse of stream bank material into a stream channel.

Bar - 

(1) Coarse grained deposit of sediment from a stream or ocean currents.
(2) A unit of measurement for quantifying force. Equivalent to 1,000,000 dynes per square centimeter.


Barchan Dune - 

Crescent shaped sand dune that has its long axis transverse to the wind and its crescent tips pointed downwind.

Barometer - 

Instrument that measures atmospheric pressure.

Barrier Beach - 

A long and narrow beach of sand and/or gravel that runs parallel to the coastline and is not submerged by the tide.

Barrier Island - 

Long, narrow islands of sand and/or gravel that are usually aligned parallel to the shore of some coasts.

Basal Sliding - 

The sliding of a glacier over the surface it rests on. Caused by the gradient of the slope and the weight of the glacier's mass.

Basalt - 

A dark colored fine grained igneous rock formed from mafic magma.

Basalt Plateau - 

Extensive continental deposits of basaltic volcanic rock.

Basaltic Magma - 

Mafic magma that forms basaltic igneous rocks.

Base - 

(1) Substance having a pH greater than 7.
(2) Substance that releases hydroxide ions (OH-).

Base Flow - 

Rate of discharge in a stream where only the throughflow and groundwater flow from subsurface aquifers contribute to the overall flow.

Base Level - 

The subterranean elevation below which a stream cannot vertically erode sediment. For many streams this hypothetical elevation is sea-level.

Basement Rock - 

Very old granite and metamorphic rocks found in continental crust. These rocks make up the continental shield.

Basin - 

A topographic rock structure whose shape is concave downwards.

Batholith - 

A large mass of subsurface intrusive igneous rock that has its origins from mantle magma.

Bay - 

A body of sheltered water found in a crescent shaped coastal configuration of land.

Bay-Mouth Bar - 

A narrow deposit of sand and/or gravel found across the mouth of a bay.

Bayhead Beach - 

An extensive deposit of sand and/or gravel in the form of a beach at the back of a bay.

Beach - 

The terrestrial interface area in between land and a water body where there are accumulations of unconsolidated sediments like sand and gravel. These deposits are laid down by the action of breaking waves.

Beach Drift - 

The lateral movement of sediments on a beach when the angles of swash and backwash differ.

Bearing - 

A system that measures in reference to the cardinal points of a compass in 90 degree quadrants.

Beaufort Wind Scale - 

Descriptive system that determines wind speed by noting the effect of the wind on the environment. Originally developed for use at sea by Admiral Beaufort of the British Navy in 1806.

Bed - 

Sedimentary structure that usually represents a layer of deposited sediment.

Bed Load - 

Portion of the stream load that is carried along the stream bed without being permanently suspend in the flowing water.

Bedding Plane - 

A layer in a series of sedimentary beds that marks a change in the type of deposits.

Bedrock - 

Rock at or near (beneath soil and regolith) the Earth's surface that is solid and relatively unweathered.

Bergschrund - 

A deep crevasse commonly found at the head of an alpine glacier. Forms when the glacial ice pulls away from the mountain side.

Berm - 

Low hill of sand that forms along coastal beaches.

Bifurcation Ratio - 

Quantitative ratio determined between the parts of systems that display branching. For example, trees have a main stem that bifurcates into smaller and smaller branches. The ratio between the branches that are derived from a larger branch or main stem is the bifurcation ratio.

Biodiversity - 

The diversity of different species (species diversity), genetic variability among individuals within each species (genetic diversity), and variety of ecosystems (ecosystem diversity). Abbreviation of biological diversity.

Biogeography - 

Field of physical geography that studies the spatial pattern of living organisms.

Biological Weathering - 

The disintegration of rock and mineral due to the chemical and/or physical agents of an organism.

Biome - 

Largest recognizable assemblage of animals and plants on the Earth. The distribution of the biomes is controlled mainly by climate.

Bioregion - 

A unique region on the Earth that has distinct soils, landforms, watersheds, climates, native plants, and animals, and/or other particular natural characteristics.

Biosphere - 

Part of the Earth where life is found. The biosphere consists of all living things, plant and animal. This sphere is characterized by life in profusion, diversity, and clever complexity. Cycling of matter in this biosphere involves not only metabolic reactions in organisms, but also many abiotic chemical reactions. Also called ecosphere.

Biotic - 

(1) Referring to life.
(2) Influences caused by living organisms.

Biotic Potential - 

Maximum rate that a population of a given species can increase in size (number of individuals) when there are no limits on growth rate.

Biotite - 

Rock forming mineral of the mica group.

Black Body - 

Is a body that emits electromagnetic radiation, at any temperature, at the maximum possible rate per unit surface area. This body also absorbs all electromagnetic radiation that is intercepted by it.

Blizzard - 

Winter severe weather condition characterized by strong wind, blowing snow, and cold temperatures.

Blowout Depression - 

Saucer shaped depressions created by wind erosion. At the leeward end of the feature there usually is a deposit of sand. Blowouts are found in coastal beach areas and in arid and semiarid regions of the world. These features are smaller than a deflation hollow.

Body Wave - 

Type of seismic wave that travels through the interior of Earth.

Bog - 

A habitat that consists of waterlogged spongy ground. Common vegetation are sedges and sphagnum moss. Bogs are common in Canada, Russia, and Scandinavia.

Bolson - 

Is a closed desert basin with no drainage outlet, surrounded by mountains.

Bora - 

Term used to describe a katabatic wind in Yugoslavia.

Bottomset Bed - 

Horizontal deltaic deposit of alluvial sediment composed of fine silt and clay.

Boulder - 

Large fragment of rock that has a diameter greater than 256 millimeters (200 millimeters in the United Kingdom).

Bowen Reaction Series - 

Model that explains the origin of the various types of igneous rocks. It suggests that the presence or absence of particular minerals in igneous rocks depends on the temperature of crystallization and on the magma's original chemical composition.

Brackish - 

Environment that is influenced by seawater with a salinity less than 35 parts per thousand (usually caused by the presence of an inflow of fresh water).

Braided Stream - 

Shallow stream channel that is subdivided into a number of continually shifting smaller channels that are separated by bar deposits.

Breaker - 

The quick collapse of an overextended water wave as it approaches the shoreline. The collapse occurs when the ratio of wave height to wavelength exceeds 1:7. This phenomenon also produces swash.

Breccia - 

Coarse grained sedimentary rock composed of cemented angular rock fragments.

Brine - 

Seawater with a salinity greater than 35 parts per thousand. Usually occurs in isolated bodies of seawater that have high amounts of water loss due to evaporation.