A fracture or a zone of fractures along which the rock on one side has been displaced relative to the rock on the other side.
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Glossary
Fault
Feldspar
A group of widespread aluminum-silicate minerals containing oxides of sodium, calcium, or potassium, which constitute 60 percent of the rocks of the Earth’s crust. Feldspar minerals occur as components of most rock types, especially igneous and metamorphic rocks.
Felsic
An igneous or metamorphic rock having abundant light-colored minerals (chiefly feldspar and quartz) in its composition; also, said of those minerals.
Fill
Soil, rock fragments, and other materials put in place by humans. Distinguished from naturally occurring, sedimentary fill.
Floodplain
The area of land between the stream channel and hillslopes where flood waters spread during periods of high flow. Floodplains can have different designations based on flood frequency – the “100-year floodplain” is the area having a 1% chance of flooding in any year.
Flow
A type of slope movement in which the water content in the displaced mass is sufficient for the material to liquefy and behave as a viscous fluid.
Fold
A product of deformation resulting in a curve or bend of a planar structure, such as rock strata, bedding planes, foliation, or cleavage.
Foot Slope
The lower, gentle slope of a hillside below a steep rock face or escarpment, including lower slopes of diminishing steepness; used here to generally designate the lower third of a hillslope.
Formation
A body of rock identified by its unique lithologic characteristics and stratigraphic position recognized as a stratigraphic unit for purposes of geologic mapping.
Fracture
A general term for any break in a rock, whether or not it causes displacement, due to mechanical failure by stress (usually a planar joint or fault surface).