Geologic Glossary
This glossary contains simplified definitions for technical terms used within this site.
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Eearthquake A sudden ground motion or vibration of the Earth. Produced by a rapid release of stored-up energy along an active fault.
eolianTerm describing the process of wind erosion, transport, and deposition, and wind-created deposits and structures such as sand dunes. EonThe largest time unit on the geologic time scale.
ephemeral streamA stream drainage that is usually dry and fills with water only during brief episodes of rainfall. Many desert streams ephemeral. epicenterThe point on the Earth's surface located directly above the focus of an earthquake.
epidoteFamily 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.
eruptionOccurs 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. extensionIn geology, the process of stretching the Earth's crust. Usually cracks (faults) form, and some blocks sink, forming sedimentary basins. extrusiveIgneous rocks that cool and solidify rapidly at or very near the Earth's surface. Also known as volcanic rocks.
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