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Geologic Glossary

This glossary contains simplified definitions for technical terms used within this site.
For more complete, technical definitions, click here.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

E

earthquake

A sudden ground motion or vibration of the Earth. Produced by a rapid release of stored-up energy along an active fault.
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eolian

Term describing the process of wind erosion, transport, and deposition, and wind-created deposits and structures such as sand dunes.

Eon

The largest time unit on the geologic time scale.
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ephemeral stream

A stream drainage that is usually dry and fills with water only during brief episodes of rainfall. Many desert streams ephemeral.

epicenter

The point on the Earth's surface located directly above the focus of an earthquake.
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epidote

Family of silicate minerals containing mostly calcium, aluminum, iron and magnesium along with water. Epidote is apple green and generally forms very small, stubby, prismatic crystals. It often occurs in veins or as a green coating on fracture surfaces. Most common in metamorphic rocks, but occasionally forms in igneous plutons that crystallize very deep in the crust.

erosion

Removal of material by water, wind, or ice.
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eruption

Occurs when solid, liquid, or gaseous volcanic materials are ejected into the Earth's atmosphere or surface by volcanic activity. Eruptions may occur as quiet lava flows or violent explosive events.

extension

In geology, the process of stretching the Earth's crust. Usually cracks (faults) form, and some blocks sink, forming sedimentary basins.

extrusive

Igneous rocks that cool and solidify rapidly at or very near the Earth's surface. Also known as volcanic rocks.
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