Glossary
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backscattered light
Atmospheric scattered sunlight that returns back to space.
backshore zone
The zone of beach that extends from a small step cut by high-tide swash to the front of the dunes or cliffs that lie farther in shore.
backswamp
The low marshy region between the bluffs and the natural levees of a floodplain.
backwash
The gravity-driven flow of water back down the slope of a beach.
badlands
Lands that are dry, unvegetated, and dissected by dendritic patterns of gullies with sharp-crested ridges between.
bajada
An elongate wedge of sediment formed by the overlap of several alluvial fans emerging from adjacent valleys.
Baltica
A Paleozoic continent that included crust that is now part of today’s Europe.
banded-iron formation (BIF)
Iron-rich sedimentary layers consisting of alternating gray beds of iron oxide and red beds of iron-rich chert.
bar
(1) A sheet or elongate lens or mound of alluvium; (2) a unit of air-pressure measurement approximately equal to 1 atm.
barchan dune
A crescent-shaped dune whose tips point downwind.
barrier island
An offshore sand bar that rises above the mean high-water level, forming an island.
barrier reef
A coral reef that develops offshore, separated from the coast by a lagoon.
basal sliding
The phenomenon in which meltwater accumulates at the base of a glacier, so that the mass of the glacier slides on a layer of water or on a slurry of water and sediment.
basalt
A fine-grained mafic igneous rock.
base level
The lowest elevation a stream channel’s floor can reach at a given locality.
basement
Older igneous and metamorphic rocks making up the Earth’s crust beneath sedimentary cover.
basement uplift
Uplift of basement faults that penetrate deep into the continental crust.
base metals
Metals that are mined but not considered precious, such as copper, lead, zinc, or tin.
basin
A fold or depression shaped like a right-side-up bowl.
Basin and Range Province
A broad, Cenozoic continental rift that has affected a portion of the western United States in Nevada, Utah, and Arizona; in this province, tilted fault blocks form ranges, and alluvium-filled valleys are basins.
batholith
A vast composite, intrusive, igneous rock body up to several hundred km long and 100 km wide, formed by the intrusion of numerous plutons in the same region.
bathymetric map
A map illustrating the shape of the ocean floor.
bathymetric profile
A cross section showing ocean depth plotted against location.
bathymetry
Variation in depth.
bauxite
A residual mineral deposit rich in aluminum.
baymouth bar
A sandspit that grows across the opening of a bay.
beach drift
The gradual migration of sand along a beach.
beach erosion
The removal of beach sand caused by wave action and longshore currents.
beach face
A steep concave part of the foreshore zone formed where the swash of the waves actively scours the sand.
bed (or stratum)
a layer of sediment or sedimentary rock with a recognizable top and bottom.
bedding
Layering or stratification in sedimentary rocks.
bed load
Large particles, such as sand, pebbles, or cobbles, that bounce or roll along a stream bed.
bedrock
Rock still attached to the Earth’s crust.
bed surface markings
features such as ripple marks, mud cracks or fossils that appear on the surface of a bed as a consequence of events that happen during deposition or soon after, while the sediment layer remains soft.
Bergeron process
Precipitation involving the growth of ice crystals in a cloud at the expense of water droplets.
berm
A horizontal or landward-sloping terrace in the backshore zone of a beach that receives sediment during a storm.
big bang theory
A cataclysmic explosion that scientists suggest represents the formation of the Universe; before this event, all matter and all energy were packed into one volumeless point.
biochemical sedimentary rock
Sedimentary rock formed from material (such as shells) produced by living organisms.
biodiversity
The number of different species that exist at a given time.
biogeochemical cycle
The exchange of chemicals between living and nonliving reservoirs in the Earth system.
bioremediation
The injection of oxygen and nutrients into a contaminated aquifer to foster the growth of bacteria that will ingest or break down contaminants.
biosphere
The region of the Earth and atmosphere inhabited by life; this region stretches from a few km below the Earth’s surface to a few km above.
bioturbation
The mixing of sediment by burrowing animals such as clams and worms.
bird's foot delta
A delta that consists of many elongate lobes that extend into the sea.
bituminous coal
Dull black coal formed at temperatures between 100° and 200°C.
black-lung disease
Lung disease contracted by miners from the inhalation of too much coal dust.
black smoker
The cloud of suspended minerals formed where hot water spews out of a vent along a mid-ocean ridge; the dissolved sulfide components of the hot water instantly precipitate when the water mixes with seawater and cools.
blind fault
A fault that does not intersect the ground surface.
blocking temperature
The temperature below which isotopes in a mineral are no longer free to move, so the radiometric clock starts.
blowout
A deep, bowl-like depression scoured out of desert terrain by a turbulent vortex of wind.
blue shift
The phenomenon in which a source of light moving toward you appears to have a higher frequency.
bluff
A long cliff (escarpment) that borders a flood plain.
body waves
Seismic waves that pass through the interior of the Earth.
bog
A wetland dominated by moss and shrubs.
bolide
A solid extraterrestrial object such as a meteorite, comet, or asteroid.
bornhardt
An inselberg with a loaf geometry, like that of Uluru (Ayers Rock) in central Australia.
Bowen’s reaction series
The sequence in which different silicate minerals crystallize during the progressive cooling of a melt.
braided stream
A sediment-choked stream consisting of entwined subchannels.
breaker
A water wave in which water at the top of the wave curves over the base of the wave.
breakwater
An offshore wall, built parallel or at an angle to the beach, that prevents the full force of waves from reaching a harbor.
breccia
Coarse sedimentary rock consisting of angular fragments; or rock broken into angular fragments by faulting.
breeder reactor
A nuclear reactor that produces its own fuel.
brine
Water that is not fresh but is less salty than seawater; brine may be found in estuaries.
brittle deformation
The cracking and fracturing of a material subjected to stress.
brittle-ductile transition (brittle-plastic transition)
The depth above which materials behave brittlely and below which materials behave ductilely (plastically); this transition typically lies between a depth of 10 and 15 km in continental crustal rock, and 60 m deep in glacial ice.
buoyancy
The upward force acting on a less dense object immersed or floating in denser material.
butte
A medium-sized, flat-topped hill in an arid region.