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 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; and (4) Higher bulk density because of the illuvial deposition of clay particles.
Back Slope - The slope on the side of a cuesta that is more gradual. Compare with the front slope.
Background Extinction - A normal extinction of species that occurs over time as a result of changes in its environmental conditions. Compare with mass extinction.
Backscattering - The portion of solar radiation directed back into space as a result of scattering in the atmosphere.
Backshore - Simply the area behind the shore. This coastal feature is located between the average spring high tide mark and the backshore slope. The backshore is occasionally influenced by wave action processes during strong cyclonic storms or extraordinarily high tides.
Backshore Slope - A coastal feature consisting of a sloping bank found landward of the shore. This coastal feature is composed of relatively non-mobile sediments.
Backswamp - Marshy, low-lying areas located on a stream's floodplain. Commonly found behind levees.
Backwash - The return water flow of swash. This sheet of water flows back into the ocean due to gravity.
Backwater - A location in a stream channel where a body of water becomes stagnant because of reduced stream flow.
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 bacterial species play a major role in nutrient cycling in ecosystems through aerobic and anaerobic decomposition. Finally, some species form symbiotic relationships with more complex organisms and help these organisms survive in the environment by fixing atmospheric nitrogen.
Badlands - (1) Term used to describe a particular landscape found in South Dakota, USA. (2) Term used to describe a semiarid landscape that has been influenced by heavy fluvial erosion. Characterized by deep ravines and gullies, round-shaped ridges, and a generally barren surface.
Bajada - A consecutive series of alluvial fans forming along the periphery of a linear mountain range. The surface of this feature undulates in a rolling fashion as one moves from the center of one alluvial fan to another. Commonly found in arid climates.
Bamboo - A flowering perennial evergreen grass that belongs to the subfamily Bambusoideae and family Poaceae. Species of bamboo can be found in a range of tropical and subtropical climates. Some species of bamboo are found at a latitude as high as 47° south. Humans have been using bamboo for food, medicine, textiles, and in the construction of a variety of products as a replacement for wood.
Bank - (1) Common term describing a slope or hillside. (2) An area of shallow seawater along a coast that has deposits of clay, silt, sand, and shells. For example, the Grand Banks of Newfoundland, Canada. (3) A raised area adjacent to the edge of a stream channel. Beyond the bank is the stream's floodplain.
Bank Caving - The process of stream bank material falling into the flowing water of a stream channel due to localized instabilities and variations in flow volume.
Bank Erosion - The removal of soil and sediment from the side of a stream channel because of erosion. Bank erosion is usually associated with increased stream flow. Vegetation located at the side of a stream channel is very effective at reducing the potential for this type of erosion.
Bank Gravel - A natural deposit of sediment that consists of a mix of gravel with sand or clay. The result of deposition along the side of a stream channel.
Bank Storage - Transient water stored in the permeable sediments found in the banks of a stream. This water often adds to stream flow as it seeps into the stream channel.
Bar - (1) Coarse-grained deposit of sediment from a stream or ocean currents. Also see bedforms. (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 crosswise to the wind and its crescent tips pointed downwind.
Barchanoid Ridge - Is a lengthy, uneven sand dune that runs at 90 degrees to the prevailing wind direction. Each barchanoid ridge consists of several barchan dunes joined to form a series of connected crescents. Each of the barchan dunes produces a wave in the barchanoid ridge. These aeolian landforms occur when the sand supply is greater than in the conditions that create a barchan dune.
Baroclinic - A condition in the atmosphere where the density of air is dependent on both temperature and atmospheric pressure. Compare with barotropic.
Barogram - The continuous record of atmospheric pressure produced by a barograph.
Barograph - A meteorological instrument that incorporates a barometer and a data recording device to produce a continuous recording of atmospheric pressure over time.
Barometer - A scientific instrument that is used to measure atmospheric pressure.
Barotropic - A condition in the atmosphere where the density of air is dependent only on atmospheric pressure. Compare with baroclinic.
Barranca - A deep, steep-sided ravine or gully.
Barrier Beach - A long and narrow beach of sand and/or gravel that runs parallel to the coastline and is not submerged by the action of tides.
Barrier Island - Long, narrow islands of sand and/or gravel that usually run parallel to the shore of some coasts.
Barrier Reef - A type of coral reef that is characterized by a lagoon or a body of water that is between the coastline and the coral reef. For example, the Great Barrier Reef consists of over 2,900 individual reef systems that stretch over a distance of 2,600 kilometers (1,600 miles) off the coast of Queensland, Australia.
Barysphere - A zone within the Earth that extends from the bottom of the lithosphere to the center of the core.
Basal Complex - The rocks found underneath the Precambrian shield deposits.
Basal Ice - A zone of ice, rich in sediment, found at the base of a glacier. The vertical extent of this layer may reach tens of meters (feet). Much of the sediment found in this ice layer is derived from the surface the glacier is sliding over.
Basal Sapping - A situation where a slope is eroded and undercut at its base.
Basal Sliding - The action of a glacier sliding over the ground surface on which it rests. Caused by the gradient of the slope, the weight of the glacier's mass, and gravity.
Basal Till - Sediments rich in clay that are moved along at the base of a glacier.
Basalt - A dark colored, fine-grained igneous rock formed from mafic magma. This common rock is normally colored grey to black. Mainly contains the minerals pyroxene, plagioclase feldspar, olivine, and amphibole.
Basalt Plateau - Extensive deposits of basalt-rich volcanic rock that have formed extensive plateaus and mountain ranges located on our planet's continents. Also called flood basalts, these deposits have formed randomly throughout Earth's geologic history during periods of enhanced volcanic activity. One explanation for their formation is the occurrence of a mantle plume in combination with continental rifting, which should produce large quantities of basaltic magma with low viscosity.
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 Cation - Soil cations belonging to the elements calcium (Ca2+), magnesium (Mg2+), potassium (K+), and sodium (Na+).
Base Exchange - See cation exchange.
Base Flow - The rate of discharge in a stream where only the throughflow and groundwater flow from subsurface aquifers contribute to the overall stream flow.
Base-level - The elevation below-ground level at which a stream cannot vertically erode sediment. For many streams, this hypothetical elevation is sea level.
Base Map - A primary map layer that is used in a geographic information system as a foundation to build a more complex mapping system. Base maps often contain spatial information such as political boundaries, water bodies, road systems, topographic features, coastlines, and feature names.
Base Saturation - Refers to the proportion of soil cation exchange sites that are occupied by cations with a positive charge.
Baseline - A measured starting point used to compare other gathered measurements, to make subsequent needed calculations, and to determine the accurate spatial location of things.
Basement Complex - Refers to an assemblage of very old igneous and metamorphic rocks created during the Archean. These rocks are found in ancient shield areas of the continents and often have sedimentary rock strata deposited on top of them.
Basement Rock - Very old igneous and metamorphic rocks found in continental crust. These rocks make up the continental shield.
Basic - Substance having a pH greater than 7. Compare with acidic.
Basic Rocks - An igneous rock that is less than 55% silica by composition. Compare this with acid rocks.
Basic Solution - Any water-based solution that is basic (pH greater than 7) or has fewer hydrogen ions (H+) than hydroxide ions (OH-). Also see acidic solution and neutral solution.
Basin - A topographic structure in the landscape whose shape is concave downwards.
Basin Discharge - The total outflow of surface stream flow and subsurface groundwater flow from a drainage basin. In some streams, basin discharge is similar to stream flow because most of the groundwater flows into the stream channel. Basin discharge can be much larger than stream flow in a drainage basin where considerable groundwater flow occurs in an extensive floodplain or where water movement is significant in wetlands outside the stream channel.
Basin Order - A morphometric calculation used in Hortonian analysis to describe the hierarchical value given to a drainage basin based on the quantitative analysis of stream segments in a drainage network.
Basin-and-Range - A term used to describe a landscape found in Nevada and Utah, USA. Characterized by mountains formed from normal faults and numerous basins that often contain lakes.
Batholith - An extremely large mass of subsurface intrusive igneous rock that has its origins in mantle magma. Compare with dyke, sill, laccolith, lopolith, and phacolith.
Bathyal Zone - A vertical zone in the oceans that has a depth of between 1,000 and 4,000 meters (3,300 to 13,100 feet). This zone has no light penetration from the surface and therefore no plant life. Seawater at this depth is about 4°C (39°F), and it generally lacks nutrients. Life is rare in this environment, and the organisms that do exist here have specific adaptations for survival. Also see (in order of depth in a water body) pelagic zone, photic zone, aphotic zone, mesopelagic zone, abyssal zone, hadal zone, demersal zone, and benthic zone.
Bathymetric - Related to the depth of water bodies.
Bathymetry - The scientific study and measurement of the depth of features in water bodies.
Bauxite - A sedimentary rock rich in aluminum hydroxide [Al(OH)3]. This economically valuable ore forms from the weathering of volcanic rocks.
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 existing as a beach at the back of a bay.
Bayou - Term used in the United States to describe an extensive body of water located in an area with little relief that is associated with a stream with low stream flow, a shallow marshy lake, or a wetland.
Beach - The terrestrial interface area 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 Cusp - A crescent-shaped beach deposit that forms because of wave action. Particle size is coarse on the crescent horns and finer in the middle of the feature.
Beach Drift - The lateral movement of sediments on a beach when the angles of swash and backwash differ.
Beach Face - The part of the beach that is influenced and shaped by wave action.
Beach Ridge - A long wave-deposited ridge of sand and sometimes coarser material running parallel to a shoreline. A beach can have multiple beach ridges as a result of successive cyclonic storms of different intensities.
Beach Rock - A sedimentary rock composed of silt, sand, gravel, shells, and coral that has formed along a shoreline. This rock tends to form in the intertidal zone and can vary from being easily breakable to well-cemented.
Beaded Drainage - A drainage pattern that consists of a number of ponds connected by a single length of stream. This pattern is commonly found in areas of permafrost, where ponds form from the localized melting of ground ice.
Beaded Esker - An esker that contains some areas of widening and narrowing in its width along its length.
Bearing - A system that measures direction relative to the four cardinal points of a compass in 90-degree quadrants. Compare with azimuth.
Bearing Capacity - The maximum average load pressure, measured in kilograms per square meter, that a soil can receive before shear failure occurs.
Beaufort Wind Scale - A descriptive system of measuring wind speed. It is accomplished by noting the effect of the wind on the environment. This system was developed in 1806 by Admiral Beaufort of the British Navy.
Bed - (1) Sedimentary structure found in streams that usually represents a layer of deposited sediment. (2) A layer of identifiable deposition in a sedimentary rock. Usually, a centimeter (half an inch) to several meters (6 to 9 feet) thick. Compare with lamina.
Bed Load - A portion of the stream load that is carried along the stream bed without permanent suspension in the flowing water. Also see dissolved load.
Bed Roughness - Normally refers to the frictional roughness of a stream bed. Roughness can be due to several factors, including bed particle size and types of bedforms found in the stream channel.
Bedding Plane - A layer in a series of sedimentary strata that marks a change in the type of deposits.
Bedforms - Depositional and erosional features found on a stream bed because of fluid flow dynamics. These features include ripples, riffles, dunes, antidunes, pools, and bars.
Bedrock - Rock at or near the Earth's surface that is solid and relatively unweathered. Bedrock is found beneath soil and regolith.
Before Present (BP) - A time scale used in Geology and other scientific disciplines that dates events and things relative to the year 1950 CE.
Belt - Term used to describe a belt-shaped zone of vegetation, climate, or geologic terrain.
Bench - A relatively narrow band of flat or gradually sloping terrain embedded in a much steeper slope.
Bench Mark - (1) A standard value used to make comparisons within a system of measurements. (2) A natural or artificial point of reference used in a topographic survey.
Benioff Zone - A zone of seismic activity descending into the upper mantle at a subduction zone that extends from near the Earth's surface to a maximum depth of about 670 kilometers (415 miles).
Benthic Zone - The ecological zone found at the lowest level of a water body, like a lake, sea, or ocean. This zone includes the surface and subsurface sediments. The various organisms found in this zone are known as the benthos. Also see (in order of depth in a water body) pelagic zone, photic zone, aphotic zone, mesopelagic zone, bathyal zone, abyssal zone, hadal zone, and demersal zone.
Benthos - The plant and animal organisms that live on the seafloor or the bottom of a lake. In oceans and seas, the benthos is usually divided into two categories: deep-sea benthos, below 200 meters (655 feet) and the littoral benthos, from 200 meters (655 feet) to the high-water spring tide level.
Bentonite - An impure clay aluminum phyllosilicate mineral that contains a significant amount of montmorillonite clay. Often forms from weathering of volcanic ash.
Berg Wind - A type of Föhn wind.
Bergschrund - A deep crevasse commonly found at the head of an alpine glacier. Develops when the glacial ice pulls away from the mountainside.
Berm - A low hill of sand that forms along coastal beaches.
Bermuda High - High pressure system that develops over the western subtropical North Atlantic. Also called the Azores High.
Bernoulli Effect - Describes what happens to the static pressure exerted on an object relative (at 90°) to the dynamic pressure that occurs when the object travels through a fluid like a gas or liquid. The upward lift associated with an airplane wing is an example of the Bernoulli Effect (however, it is only one of two factors that cause planes to fly). As air passes either side of the wing, it travels at different speeds because of the wing's shape. The curved shape of the wing top causes the air to travel faster than the air below. This increase in speed initiates a lowering of atmospheric pressure and results in a lifting force, causing the plane to fly. Also called the Bernoulli Principle.
Beta Diversity - A measure of species diversity that focuses on the difference in the number of species between smaller subunits located in the broader landscape. Introduced by ecologist R. H. Whittaker. Compare with alpha diversity and gamma diversity.
Beta Particle - An electron emitted from the nucleus of a radioactive isotope. Also see alpha particle and gamma rays.
Biennial Plant - A plant species that completes its life in two growing seasons.
Bifurcation Ratio - A 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.
Big Bang - Theory that suggests that about 13.8 billion years ago, all the matter and energy in the Universe was concentrated into an extremely small area. At this instant, matter, energy, space, and time did not exist. Then suddenly, the Universe began to expand at an incredible rate and matter, energy, space, and time came into being. As the Universe inflated, matter began to coalesce into gas clouds, and then stars and planets. Some scientists believe that this expansion is finite and will one day cease. After this time, the Universe will begin to collapse until a Big Crunch occurs.
Big Crunch - Collapse of the Universe into its original form before the Big Bang. At the end of this process, matter, energy, space, and time will not exist.
Bight - A large-scale, long indent, or open bay along a coastline.
Billabong - An Aboriginal term from Australia that describes a stream with a temporary flow because of variations in precipitation.
Billow Clouds - See wave clouds.
Bimodal Distribution - A common probability distribution displayed by a representative data sample or the whole population of some quantitatively measurable variable. If the values of this distribution are plotted on a graph's horizontal axis and their frequencies on the vertical axis, the resulting pattern shows two distinct peaks. Compare with the normal distribution.
Bioaccumulate - Is the buildup of a substance inside an organism to levels that are much higher than its concentration in the surrounding environment. This condition can occur with substances that are harmful to the organism, like pesticides, heavy metals, and other toxic substances.
Biochemical Oxygen Demand (BOD) - A commonly used measure of organic pollution in water. The measurement of BOD involves quantifying the amount of oxygen [in milligrams (mg)] consumed by microorganisms over 5 days at a temperature of 20°C (68°F) in a liter of water. Pristine water can have a BOD that is less than 1 mg/liter, while untreated sewage can have values between 200 to 600 mg/liter.
Biochore - A collection of similar biotopes.
Biochronology - (1) A time scale used in science-based on changes in the fossil record. (2) The study of the evolution of life as it relates to the geologic time scale. (3) Relative dating of geologic events based on information in a biostratigraphy.
Biocide - A chemical substance or organism that is used to attract, deter, cause reduced growth or reproduction or the death of a living organism. Some biocides are toxic. The following are considered types of biocide: herbicide, insecticide, fungicide, and pesticide. Some other examples of biocides include antibiotics, disinfectants, antiseptics, and preservatives.
Bioclastic - Made from shell fragments or other types of organic remains. In Geology, this term is often used to describe the physical characteristics of a rock.
Bioclimatology - The scientific study of the cause and effect relationships and processes that exist between climate and living organisms, including human beings.
Biocoenosis - Refers to the biological community for a particular habitat that consists of both plants and animals.
Biodegradation - This term refers to microorganisms degrading or altering organic or inorganic chemicals found in the environment through metabolic or enzymic processes.
Biodiversity - A term describing the assortment of living organisms through the combined effect of three different measures: species diversity, genetic variability among individuals within each species (genetic diversity), and the variety of ecosystems (ecosystem diversity). Abbreviation of the term biological diversity.
Biodiversity Hotspot - Is a biogeographic region on the Earth that has levels of genetic diversity, species diversity, and/or ecosystem diversity that are considerably higher than the surrounding areas. These locations are often at risk of losing biodiversity due to human activity. This concept was first described by Norman Myers in 1988. In 2000, Myers and others developed specific criteria for identifying biodiversity hotspots, which were published in the journal Nature. In this publication, twenty-five regions were recognized as biodiversity hotspots. Much more work has been done on this idea since it was first proposed.
Biofacies - (1) Within strata, differences in fossils that occur across the horizontal distribution of the sedimentary rock layer. (2) Collections of living organisms that formed at the same point in time but under different environmental conditions.
Biogenic Sediment - Sediment that forms from the remains of living organisms.
Biogeochemical Cycling - Cycling of a single element, compound, or chemical by various abiotic and biotic processes through the various stores found in the biosphere, lithosphere, hydrosphere, and atmosphere.
Biogeocoenosis - Refers to the biological community that consists of both plants and animals and the interacting physical (abiotic) environment for a particular habitat.
Biogeographic Realm - The classification of the Earth's terrestrial surface into eight regions (realms) where the geographic distribution (biogeography) of plants and animals is unique and overlapping. These regions differ in species composition due to geographic barriers that restrict migration between realms. As a result of geographic isolation, the species common to a realm have a shared evolutionary history. The names of the eight realms are (World Wildlife Fund scheme): Paleoarctic; Nearctic; Afrotropic; Neotropic; Australasian; Indomalaya; Oceania; and Antarctic.
Biogeography- (1) A field of physical geography that studies the spatial pattern of living organisms. (2) The geographic distribution of plants and animals on the Earth.
Biogeomorphology - The geomorphological study of plants and animals as agents in landscape processes and forms.
Bioherm - An ancient coral reef from Earth's geologic past.
Biokarst - A type of karst landform composed of limestone bedrock and dominated by geomorphic features created by biotic processes of plants and animals. These biotic processes can include enhanced solution chemical weathering due to the formation of chelates and erosion through boring, digging, and digestive action.
Biological Amplification - Increase in concentration of toxic fat-soluble chemicals in organisms at successively higher trophic levels of a grazing food chain or food web because of the consumption of organisms at lower trophic levels.
Biological Control - The suppression of pest organism numbers by biological means. Many different techniques have been used to achieve this goal, for example: using insect herbivores to consume weeds, using predators to control pests, and using pathogens and parasites to control pests.
Biological Magnification - Is the increased concentration of substances in the bodies of organisms as one moves up the grazing food chain or through a food web because of consumption. One of the most famous examples of biological magnification involved the insecticide DDT (dichlorodiphenyltrichloroethane) and predatory birds in the United States. Starting in the late 1930s and early 40s, DDT was heavily used in the United States to control many common insect pests. DDT was quite persistent in the environment, and some of it ended up in aquatic systems, where it was incorporated into the bodies of phytoplankton, which were eaten by zooplankton (primary consumers). In phytoplankton and zooplankton, the concentration of DDT in their tissues was about 0.04 ppm. The zooplankton were then consumed by fish (secondary consumers) in large numbers, and the DDT became highly concentrated in the fatty tissues (0.5-2.0 ppm). In turn, the fish were consumed by predatory birds like hawks, peregrine falcons, bald eagles, osprey, and brown pelicans (tertiary consumers). In these birds, DDT concentrations in their tissues reached about 25 ppm. By the 1950s, it became clear that these birds were experiencing significant declines in numbers. This decline was believed to be caused by DDT, which made eggshells too thin for successful hatching. The United States Environmental Protection Agency banned DDT in 1971. Also referred to as biomagnify and biomagnification.
Biological Productivity - Is the amount of biomass or its equivalent (in the form of dry matter, carbon, or energy content) produced for some unit area per interval of time. Consists of two related and overlapping parts: primary productivity and secondary productivity. Also see gross primary productivity, net primary productivity, gross secondary productivity, and net secondary productivity.
Biological Resource - A substance or thing (resource) required by a living organism for its survival and fitness.
Biological Weathering - The disintegration of rock and minerals due to the chemical and/or physical agents of an organism. Compare with physical weathering and chemical weathering.
Bioluminescence - Is the ability of an organism to produce and emit light. Some species of jellyfish can do this.
Biomass - The weight of living tissues is usually measured per unit area over a particular time interval. Biomass can include the dead parts of organisms, such as bark, hair, and nails.
Biome - The largest recognizable assemblage of plants and animals on the Earth. The distribution of biomes is mainly controlled by climate.
Biometeorology - A subfield of meteorology that studies the effects of weather and climate on life, including humans.
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, plants and animals. 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 the ecosphere.
Biostratigraphy - A series of layers in a stratum that can be differentiated from sedimentary layers above and below it by its unique assemblage of fossils.
Biota - Refers to all of the species of organisms found in a given area.
Biotechnology - Is the application of scientific knowledge regarding organisms and biological processes to industry, engineering, or any other practical purpose related to human needs and well-being.
Biotic - (1) Referring to life. (2) An influence caused by living organisms.
Biotic Interaction - Mutual or reciprocal influence between two or more similar organisms or individuals of different species. The major biotic interactions are: competition, mutualism, predation, parasitism, amensalism, and commensalism.
Biotic Isolation - The isolation of one species from other similar, related cohabiting species because hereditary mechanisms do not allow for interbreeding. Compare with geographic isolation.
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 - A rock-forming mineral of the mica group.
Biotope - A small area or habitat of relatively uniform environmental conditions found within a more complex and environmentally variable ecosystem.
Bioturbation - The mixing and displacement of soil or sediments because of the action of organisms. For example, soil mixing due to an animal's burrowing.
Birch Discontinuity - See Repetti Discontinuity.
Bird - A group of warm-blooded vertebrate animals whose bodies are covered with feathers. There are 10,906 different species of birds living on our planet today (according Cornell Lab of Ornithology). The fossil record suggests that birds first evolved on Earth about 160 million years ago. About 120 to 130 species have gone extinct in the last 300 years due to direct and indirect human activities.
Bise (Bize) - A term used in France and Switzerland to describe a cold and often dry winter wind that comes from the north or the northeast.
Bishop's Ring - A diffused reddish-brown halo layer seen circling the Sun after sizeable explosive volcanic eruptions.
Bitumen - See asphalt.
Bituminous - Something that contains or is related to bitumen/asphalt.
Black Body - A body or object that emits electromagnetic radiation, at any temperature, at the maximum possible emission rate per unit surface area. A black body also absorbs all electromagnetic radiation it intercepts.
Black Box System - A system that is understood only in terms of input and output. Nothing is known about the cause-and-effect processing working inside the black box that produces the output.
Black Smoker - A common type of hydrothermal vent found on the ocean floor that emits black smoke. The particular black color occurs because of the presence of sulfides.
Blanket Bog - A large expanse of peat of variable depth that exists not only in hollows but over undulating topography. Blanket bogs are found in the middle to high latitudes all across the Northern Hemisphere, where a cool climate, high rainfall, and low evapotranspiration favor the growth of peat. Also called blanket mire and featherbed bog.
Blind Valley - Refers to a deep, narrow, flat-bottomed stream-eroded valley that suddenly ends. This type of valley commonly forms in karst landscapes when a stream flows over limestone bedrock, cutting a deep valley and then abruptly dropping below-ground into a subterranean cave.
Blizzard - Severe weather condition that occurs in winter and is characterized by strong winds, blowing snow, and cold temperatures. Often caused by an intense mid-latitude cyclone.
Block - A boulder-sized fragment of rock that is very angular in shape. More than 200 millimeters or 7.9 inches in diameter (256 millimeters or 10 inches in the USA).
Block Diagram - An illustration technique used in the sciences to represent a phenomenon in a three-dimensional rectangle where up to three sides can be observed.
Block Faulting - A tectonic process where tensional stresses cause the landscape to fracture and fault into blocks. This process causes some blocks of land to subside while other pieces are pushed up. Produces normal, reverse, graben, and horst faults.
Block Fields - A continuous stretch of angular boulders created by frost action acting on the bedrock. Common in periglacial environments.
Blocking - A meteorological term that refers to the stagnation of atmospheric circulation in the surface westerlies near the polar front. This results in changes in the usual west-to-east migration patterns of mid-latitude cyclones and associated high pressure systems. Blocking causes persistent weather conditions over affected areas for extended periods.
Blocking High - A high pressure system that is nearly stationary or moves slowly relative to the usual west-to-east flow of surface westerlies near the polar front. This condition also restricts the west-to-east migration of mid-latitude cyclones. Also called a blocking anticyclone.
Blood Rain - A rare meteorological event where rain is colored red because of the presence of dust. Blood rain occurs occasionally in Europe when dust from the Sahara is carried into the atmosphere by wind.
Blowhole - A vertical shaft that connects a horizontal sea cave to the ground surface. Seawater from incoming waves or rising tides can be forced through this opening with great force, forming a powerful vertical jet of water.
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 worldwide. These features are smaller than a deflation hollow.
Blue Hole - A roughly circular-submarine sinkhole located in limestone sedimentary deposits found along the coast.
Blue Mud - A sediment deposit found at deep depths in the ocean that is composed of a mixture of clay, silt, and organic matter. Blue mud gets its color from iron sulfide and chemical reduction.
Bluff - A term commonly used to describe a cliff with a steep vertical edge.
Bodden - A term used to describe irregularly shaped inlets found along the Baltic coast of Germany.
Body Wave - A type of seismic wave that travels through the interior of the Earth.
Bog - A low-lying, flooded habitat that consists of waterlogged, spongy ground with deep accumulations of acidic peat. Surface water and groundwater of bogs are usually acidic and nutrient-poor. Often found in association with boreal forest. Vegetation commonly found in these habitats includes various species of sedges and sphagnum moss. Bogs are common in Canada, Russia, and Scandinavia. Compare with fen.
Bog Burst - A sudden release of water and saturated loose peat from a bog. Bog bursts can be triggered by excessive precipitation that causes water and saturated peat to spill over somewhere along the bog's edge.
Boghead Coal - A brown or black colored form of bituminous coal or oil shale. Also called cannel coal.
Bole - Another term commonly used to describe a tree trunk.
Bølling Interstadial - A relatively short interstadial that occurred from 12,000 to 13,000 BP (before present) during the last major glacial advance of the Pleistocene Epoch.
Bolson - Is a closed desert basin surrounded by mountains. Any water entering this basin has no way to drain out.
Bone Bed - A sedimentary rock stratum or other deposit rich in the (fossilized) bones of organisms.
Bora - Term used to describe a katabatic wind in Yugoslavia.
Bore - Is a wave or series of waves associated with an incoming flood tide flowing into a stream or a narrow bay. Bores are uncommon, occurring only in areas of the world that have a large tidal range, usually greater than 6 meters (20 feet).
Boreal Climate - The climate associated with the boreal forest biome. According to the Köppen Climate Classification system, this climate is found under the Moist Mid-Latitude Climates with Cold Winters (D Climate) major climatic type and has the specific designations Dfc, Dwc, and Dsc.
Boreal Forest - High to mid-latitude biome dominated by coniferous forest. Predominant vegetation of this biome is various coniferous tree species, including spruce, fir, pine, and cedars. Also called Taiga.
Borehole - A hole drilled into the Earth's crust for commercial or scientific analysis. The most common purpose of drilling a borehole is to explore resources.
Bottom Water - Usually refers to the bottommost layer of seawater in an ocean. Three important characteristics of ocean bottom water include it has a temperature between 0°C to 3°C, a salinity if 3.5%, and is very dense. Also called deep ocean water.
Bottomset Bed - Horizontal deltaic deposit of alluvial sediment composed of fine silt and clay.
Boulder - Large fragment of rock that is more than 200 millimeters or 7.9 inches in diameter (256 millimeters or 10 inches in the USA and with the Wentworth Scale greater than 0.0039 to 0.0625 millimeters). Compare with clay, silt, sand, gravel, and cobble.
Boulder Clay - Another term used to describe glacial till.
Boulder Train - A linear or fan-shaped deposit of boulders that were glacially transported from an identifiable bedrock source. The presence of these features is often used to determine past glacier movements.
Boundary - A division that separates two measurably different phenomena across space or time.
Boundary Current - A major ocean current that has its pattern of flow influenced by the presence of a continental coastline. There are two types of boundary currents: western boundary currents and eastern boundary currents.
Boundary Layer - A layer of air found immediately above the surface of an object. This layer interacts with the object and the atmosphere above it. This concept can be applied to objects of greatly varying sizes. Meteorologists considered our planet's boundary layer to be a zone about one to two kilometers (0.5 to 1.2 miles) adjacent to the ground surface. The boundary layer of a leaf on a plant may be only a few millimeters (about 0.1 inches) thick.
Boundary Waves - Waves that exist within a water body that are different from the waves seen on its surface. Also called internal waves.
Bowen Ratio - The calculated ratio of sensible heat to latent heat transfer from the Earth's ground surface up into the atmosphere. Mathematical it can be expressed as:
Bowen Ratio = Sensible Heat Flux / Latent Heat Flux
Bowen Reaction Series - A model that explains the origin of the various types of igneous rocks. This model suggests that the presence or absence of particular minerals in igneous rocks depends on the temperature of crystallization and the magma's original chemical composition.
Boyle's Law - Law describing the ideal relationship of a gas between pressure and volume. Expressed by the scientist Robert Boyle in 1662. This law states that, in a closed system, the absolute pressure of a gas is inversely proportional to its volume when the temperature and the amount of gas are held constant.
BP - Abbreviation for before present.
Brackish - An environment that is influenced by seawater and has a salinity of less than 35 parts per thousand (usually caused by the presence of an inflow of freshwater).
Braided Stream - A shallow stream channel that is subdivided into a number of continually shifting smaller channels that are separated by bar deposits.
Brash - (1) An accumulation of fractured rock that has been weathered in place. (2) A mixture of broken rock or ice.
Braunerde - A German term that simply translates to brown earth soil.
Breached Anticline - A deeply eroded anticline where the strata layers become younger as one moves away from the center of rock formation.
Breaker - The quick collapse of an overextended water wave as it approaches the shoreline. The collapse occurs when the wave height-to-wavelength ratio exceeds 1:7. This phenomenon also produces swash.
Breakpoint Bar - Zone of coarse-grained bar deposits found offshore where ocean waves first break.
Breccia - A coarse-grained sedimentary rock composed of cemented angular rock fragments.
Breeze - A low-speed wind. The Beaufort Wind Scale defines five types of breeze: light breeze from 6 to 11 kph (kilometers per hour); gentle breeze from 12 to 19 kph; moderate breeze from 20 to 28 kph; fresh breeze from 29 to 38 kph; and strong breeze from 39 to 49 kph.
Brine - Seawater with a salinity greater than 35 parts per thousand. Brine usually forms in isolated bodies of seawater that experience significant water loss due to evaporation.
British Thermal Unit (Btu) - A measurement unit for heat. It is the amount of energy required to raise the temperature of 1 pound of water by 1° Fahrenheit from 62° to 63°. One Btu is equal to 252 calories and to 1,055 joules.
Bromeliad - Plants of the bromeliad family (Bromeliaceae). These plants grow in a variety of habitats, from the dry deserts of the subtropics to the equatorial tropical rainforests. Many bromeliads grow high up on the branches and trunks of trees in the tropical rainforest. Relative to growth habits and other characteristics, Bromeliaceae is divided into the subfamilies Pitcairnioideae, Tillandsioideae, and Bromelioideae.
Bronze Age - A period in human history defined by the use of bronze, the development of early writing systems, and the early development of urban culture. Dates for the Bronze Age vary by region: Near East, 3300 to 1200 BCE; South Asia, 3000 to 1200 BCE; Europe, 3200 to 600 BCE; and China, 2000 to 700 BCE.
Brown Coal - See lignite.
Brown Earth Soil - Is a soil that commonly develops under deciduous forest in the mid-latitudes. Their red-to-brown color develops because of the translocation of aluminum and iron oxides in the A horizon down to the B horizon. These soils are generally well-drained, have a nutrient-rich litter layer, and support vigorous biological activity. These soils are extensively used for agriculture.
Brückner Cycle - A climate cycle of about 33 to 36 years in length, where a series of seasons with wet and cold weather is followed by a series of dry, hot seasons.
Brunisol Soil - Soil order (type) of the Canadian System of Soil Classification. This soil type is associated with forest vegetation. It is usually poorly developed and immature. The most identifying trait of this soil is the presence of a brown B horizon. For more information on this soil type, see the textbook Canadian System of Soil Classification, 3rd Edition, available online - https://sis.agr.gc.ca/cansis/publications/manuals/1998-cssc-ed3/index.html.
Brunizem - A brown soil that develops under semiarid grassland vegetation in the mid-latitudes. Similar to a mollisol.
Bruun Rule - A model that mathematically predicts how a change in local sea level will change the horizontal position of the shoreline. This model assumes that a beach profile is generally concave upward. Further, a rise in sea level will cause the erosion of sand from the beach face and deposition of these sediments offshore in order to maintain a constant water depth. The Bruun rule is described by the following equation: r = ls/h where r is shoreline change, s is the change in sea level, l is the cross-shore distance, and h is the height of the equilibrium cross-shore profile from beach crest to offshore.
Bubnoff Units (B) - Standard unit of measurement used to quantify erosion rates on slopes or ground surfaces. One Bubnoff unit is equal to 1 millimeter in 1,000 years, or it is equal to 1 m3 of material being removed from an area of 1 square kilometer in 1 year.
Buffer - Is a natural or human-made solution that can keep pH at a nearly constant value even when a small amount of strong acid or base is added to it. Human blood is an example of a natural buffer.
Bulk Density - Is a measure of a soil's mass relative to the volume it occupies. Bulk density is mainly influenced by two factors: soil mineral content and inter-particle compaction. Usually expressed in grams per cubic centimeter after the soil has been dried to a constant weight at 105°C.
Bulk Specific Gravity - Measurement used in soil science to determine the relative density of a soil or sediment. Determined by finding the ratio of the bulk density of a soil to the mass of the same unit volume of water.
Buried Topography - A landscape terrain that has become subsequently buried over by deposited sediments.
Bush Encroachment - (1) The natural transformation of a grass-dominated habitat to a tree and/or shrub-dominated habitat because of plant succession. This change may be due to a reduction in fire disturbance. (2) The transformation of a once cultivated area previously cleared of natural vegetation into a tree and/or shrub-dominated habitat because of plant succession.
Bushveld - Specific name given to a region of savanna vegetation found in South Africa, Botswana, and Zimbabwe. The grassed plain of this habitat is interspersed with dense groups of trees and shrubs. During the winter dry season, the grasses stop growing, turn yellow or brown, and many trees and shrubs drop their leaves. This habitat is home to White Rhino, Black Rhino, Blue Wildebeest, Kudu, Impala, and various antelope species.
Butte - Is an isolated hill on a relatively level plain, with steep sides and a flat top. These landscape features are common in arid to semiarid climates and often represent remnants of a much older land surface that have survived erosion processes due to the presence of a caprock.
Buys Ballot's Law - Describes the spatial relationship between wind direction and atmospheric pressure distribution. In the Northern Hemisphere, it states: for a person who has their back to the wind, the high pressure system would be on their right and the low pressure system on their left. In the Southern Hemisphere, it states: for a person who has their back to the wind, the high pressure system would be on their right and the low pressure system on their left. First stated in 1857 by Dutch meteorologist C.H.D. Buys Ballot.
Bysmalith - An igneous intrusion of rock that is roughly cylindrical and vertically oriented. This geologic feature is forced upward into overlying strata, causing these layers to dome and fracture. Bysmaliths are typically composed of granite or granodiorite rock, and they often form mountains.
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