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.

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.

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.