Choose a letter:

a   b   c   d   e   f   g   h   i   j   k   l   m   n   o   p   q   r   s   t   u   v   w   x   y   z

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 inshore.
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.
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.
base metals	Metals that are mined but not considered precious. Examples include copper, lead, zinc, and tin.
basement	Older igneous and metamorphic rocks making up the Earth’s crust beneath sedimentary cover.
basement uplift	Uplift of basement rock by faults that penetrate deep into the continental crust.
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.
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 steeply concave part of the foreshore zone formed where the swash of the waves actively scours the sand.
bed load	Large particles, such as sand, pebbles, or cobbles, that bounce or roll along a stream bed.
bedding	Layering or stratification in sedimentary rocks.
bedrock	Rock still attached to the Earth’s crust.
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	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.
bituminous coal	Dull, black intermediate-rank coal formed at temperatures between 100° and 200°C.
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.
black-lung disease	Lung disease contracted by miners from the inhalation of too much coal dust.
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.
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 that explodes in the atmosphere.
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	The depth above which materials are rigid and break easily and below which materials behave 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-size, flat-topped hill in an arid region.