Glossary
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fault
A fracture on which one body of rock slides past another.
fault-block mountains
An outdated term for a narrow, elongate range of mountains that develops in a continental-rift setting as normal faulting drops down blocks of crust, or tilts blocks.
fault breccia
Fragmented rock in which angular fragments were formed by brittle fault movement; fault breccia occurs along a fault.
fault creep
Gradual movement along a fault that occurs in the absence of an earthquake.
fault gouge
Pulverized rock consisting of fine powder that lies along fault surfaces; gouge forms by crushing and grinding.
faulting
Slip events along a fault.
fault scarp
A small step on the ground surface where one side of a fault has moved vertically with respect to the other.
fault system
A grouping of numerous related faults.
fault trace (or line)
The intersection between a fault and the ground surface.
Ferrel cell
The name given to the middle-latitude convection cells in the atmosphere.
fetch
The distance across a body of water along which a wind blows to build waves.
fine-grained
A textural term for rock consisting of many fine grains or clasts.
firn
Compacted granular ice (derived from snow) that forms where snow is deeply buried; if buried more deeply, firn turns into glacial ice.
fission track
A line of damage formed in the crystal lattice of a mineral by the ejection of an atomic particle during the decay of a radioactive isotope.
fissure
A conduit in a magma chamber in the shape of a long crack through which magma rises and erupts at the surface.
fjord
A deep, glacially carved, U-shaped valley flooded by rising sea level.
flank eruption
An eruption that occurs when a secondary chimney, or fissure, breaks through the flank of a volcano.
flash flood
A flood that occurs during unusually intense rainfall or as the result of a dam collapse, during which the floodwaters rise very fast.
flexing
The process of folding in which a succession of rock layers bends and slip occurs between the layers.
flocculation
The clumping together of clay suspended in river water into bunches that are large enough to settle out.
flood
An event during which the volume of water in a stream becomes so great that it covers areas outside the stream’s normal channel.
flood basalt
Vast sheets of basalt that spread from a volcanic vent over an extensive surface of land; they may form where a rift develops above a continental hot spot, and lava is particularly hot and has low viscosity.
floodplain
The flat land on either side of a stream that becomes covered with water during a flood.
floodplain flood
A flood during which a floodplain is submerged.
flood stage
The stage when water reaches the top of a stream channel.
flood tide
The rising tide.
floodway
A mapped region likely to be flooded, in which people avoid constructing buildings.
flow fold
A fold that forms when the rock is so soft that it behaves like weak plastic.
flowstone
A sheet of limestone that forms along the wall of a cave when groundwater flows along the surface of the wall.
fluvial deposit
Sediment deposited in a stream channel, along a stream bank, or on a floodplain.
flux
Flow.
focus
The location where a fault slips during an earthquake (hypocenter).
fog
A cloud that forms at ground level.
fold
A bend or wrinkle of rock layers or foliation; folds form as a consequence of ductile deformation.
fold axis
An imaginary line that, when moved parallel to itself, can trace out the shape of a folded surface.
fold-thrust belt
An assemblage of folds and related thrust faults that develop above a detachment fault.
foliation
Layering formed as a consequence of the alignment of mineral grains, or of compositional
banding in a metamorphic rock.
footwall
The rock mass that lies below the fault plane
foraminifera
Microscopic plankton with calcitic shells, components of some limestones.
force
= mass x acceleration. In other words, a force, when applied to a mass, causes the mass to change its velocity (accelerate or decelerate).
foreland sedimentary basin
A basin located under the plains adjacent to a mountain front, which develops as the weight of the mountains pushes the crust down, creating a depression that traps sediment.
foreshocks
The series of smaller earthquakes that precede a major earthquake.
foreshore zone
The zone of beach regularly covered and uncovered by rising and falling tides.
formation
Stratigraphic formation.
fossil
The remnant, or trace, of an ancient living organism that has been preserved in rock or sediment.
fossil assemblage
A group of fossil species found in a specific sequence of sedimentary rock.
fossil correlation
A determination of the stratigraphic relation between two sedimentary rock units, reached by studying fossils.
fossil fuel
An energy resource such as oil or coal that comes from organisms that lived long ago, and thus stores solar energy that reached the Earth then.
fossiliferous limestone
Limestone consisting of abundant fossil shells and shell fragments.
fossilization
The process of forming a fossil.
fractional crystallization
The process by which a magma becomes progressively more silicic as it cools, because early-formed crystals settle out.
fracture zone
A narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to a mid-ocean ridge, and the actively slipping part of a fracture zone is a transform fault.
fresh rock
Rock whose mineral grains have their original composition and shape.
friction
Resistance to sliding on a surface.
fringing reef
A coral reef that forms directly along the coast.
front
The boundary between two air masses.
frost wedging
The process in which water trapped in a joint freezes, forces the joint open, and may cause the joint to grow.
fuel rod
A metal tube that holds the nuclear fuel in a nuclear reactor.
Fujita scale
A scale that distinguishes among tornadoes based on wind speed, path dimensions, and possible damage.