OREGON STATE UNIVERSITY

Glossary beginning with F

Volcano Term Definitions

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Fault

A crack or fracture in the earth's surface. Movement along the fault can cause earthquakes or--in the process of mountain-building--can release underlying magma and permit it to rise to the surface.

Fault Scarp

A steep slope or cliff formed directly by movement along a fault and representing the exposed surface of the fault before modification by erosion and weathering.

Felsic

An igneous rock having abundant light-colored minerals.

Fire fountain

A rhythmic vertical fountainlike eruption of lava.

Fissures

Elongated fractures or cracks on the slopes of a volcano. Fissure eruptions typically produce liquid flows, but pyroclastics may also be ejected.

Flank Eruption

An eruption from the side of a volcano (in contrast to a summit eruption.)

Fluvial

Produced by the action of of flowing water.

Formation

A body of rock identified by lithic characteristics and stratigraphic position and is mappable at the earth's surface or traceable in the subsurface.

Fracture

The manner of breaking due to intense folding or faulting.

Fumarole

A vent or opening through which issue steam, hydrogen sulfide, or other gases. The craters of many dormant volcanoes contain active fumaroles.