OREGON STATE UNIVERSITY

Glossary beginning with D

Volcano Term Definitions

d
Dacite

Volcanic rock (or lava) that characteristically is light in color and contains 62% to 69% silica and moderate a mounts of sodium and potassium.

Debris Flow

A mixture of water-saturated rock debris that flows downslope under the force of gravity (also called lahar or mudflow).

Devonian

A period of time in the Paleozoic Era that covered the time span between 400 and 345 million years.

Diatreme

A breccia filled volcanic pipe that was formed by a gaseous explosion.

Dome

A steep-sided mass of viscous (doughy) lava extruded from a volcanic vent (often circular in plane view) and spiny, rounded, or flat on top. Its surface is often rough and blocky as a result of fragmentation of the cooler, outer crust during growth of the dome.

Dome

Mass of lava, created by many individual flows, that has built a dome-shaped pile of lava.

Dormant

The term is used to describe a volcano which is presently inactive but which may erupt again. Most of the major Cascade volcanoes are believed to be dormant rather than extinct.

Drainage Basin

The area of land drained by a river system.