OREGON STATE UNIVERSITY

Glossary beginning with M

Volcano Term Definitions

m
Maarsearch for term

A volcanic crater that is produced by an explosion in an area of low relief, is generally more or less circular, and often contains a lake, pond, or marsh.

Maficsearch for term

An igneous composed chiefly of one or more dark-colored minerals.

Magmasearch for term

Molten rock beneath the surface of the earth.

Magma Chambersearch for term

The subterranean cavity containing the gas-rich liquid magma which feeds a volcano.

Magmaticsearch for term

Pertaining to magma.

Magnitudesearch for term

A numerical expression of the amount of energy released by an earthquake, determined by measuring earthquake waves on standardized recording instruments (seismographs.) The number scale for magnitudes is logarithmic rather than arithmetic. Therefore, deflections on a seismograph for a magnitude 5 earthquake, for example, are 10 times greater than those for a magnitude 4 earthquake, 100 times greater than for a magnitude 3 earthquake, and so on.

Mantlesearch for term

The zone of the earth below the crust and above the core.

Matrixsearch for term

The solid matter in which a fossil or crystal is embedded. Also, a binding substance (e.g., cement in concrete).

Miocenesearch for term

An epoch in Earth's history from about 24 to 5 million years ago. Also refers to the rocks that formed in that epoch.

Mohosearch for term

Also called the Mohorovicic discontinuity. The surface or discontinuity that separates the crust from the mantle. The Moho is at a depth of 5-10 km beneath the ocean floor and about 35 km below the continents (but down to 60 km below mountains). Named for Andrija Mohorovicic, a Croatian seismologist.

Monogeneticsearch for term

A volcano built by a single eruption.

Mudflowsearch for term

A flowage of water-saturated earth material possessing a high degree of fluidity during movement. A less-saturated flowing mass is often called a debris flow. A mudflow originating on the flank of a volcano is properly called a lahar.