OREGON STATE UNIVERSITY

Glossary beginning with R

Volcano Term Definitions

r
Reliefsearch for term

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

Renewed Volcanism Statesearch for term

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.

Reposesearch for term

The interval of time between volcanic eruptions.

Rhyodacitesearch for term

An extrusive rock intermediate in composition between dacite and rhyolite.

Rhyolitesearch for term

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

Rift Systemsearch for term

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 Zonesearch for term

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

Ring of Firesearch for term

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