Glossary beginning with R

Volcano Term Definitions


The vertical difference between the summit of a mountain and the adjacent valley or plain.

Renewed Volcanism State

Refers to a state in the evolution of a typical Hawaiian volcano during which --after a long period of quiescence--lava and tephra erupt intermittently. Erosion and reef building continue.


The interval of time between volcanic eruptions.


An extrusive rock intermediate in composition between dacite and rhyolite.


Volcanic rock (or lava) that characteristically is light in color, contains 69% silica or more, and is rich in potassium and sodium.

Rift System

The oceanic ridges formed where tectonic plates are separating and a new crust is being created; also, their on-land counterparts such as the East African Rift.

Rift Zone

A zone of volcanic features associated with underlying dikes. The location of the rift is marked by cracks, faults, and vents.

Ring of Fire

The regions of mountain-building earthquakes and volcanoes which surround the Pacific Ocean.