OREGON STATE UNIVERSITY

Glossary beginning with S

Volcano Term Definitions

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Scoria

A bomb-size (> 64 mm) pyroclast that is irregular in form and generally very vesicular. It is usually heavier, darker, and more crystalline than pumice.

Seamount

A submarine volcano

Shearing

The motion of surfaces sliding past one another.

Shield Volcano

A gently sloping volcano in the shape of a flattened dome and built almost exclusively of lava flows.

Silica

A chemical combination of silicon and oxygen

Sill

A tabular body of intrusive igneous rock, parallel to the layering of the rocks into which it intrudes.

Skylight

An opening formed by a collapse in the roof of a lava tube

Spatter Cone

A low, steep-sided cone of spatter built up on a fissure or vent. It is usually of basaltic material

Spines

Horn-like projections formed upon a lava dome.

Stratovolcano

A volcano composed of both lava flows and pyroclastic material.

Strombolian

A type of volcanic eruption characterized by jetting of clots or fountains of fluid basaltic lava from a central crater

Subduction Zone

The zone of convergence of two tectonic plates, one of which usually overrides the other.

Surge

A ring-shaped cloud of gas and suspended solid debris that moves radially outward at high velocity as a density flow from the base of a vertical eruption column accompanying a volcanic eruption or crater formation.