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EARTHFLOW: A fluid mass movement of mainly fine-grained material, along with some broken rock, at slow or moderate speeds.

EARTHQUAKE: The violent motion of the ground caused by the passage of seismic waves radiating from a fault along which sudden movement has taken place.

EBB TIDE: The part of the tide cycle during which the water level is falling.

ECLOGITE: An extremely high grade metamorphic rock containing the minerals garnet and pyroxene.

EFFLUENT STREAM: A stream or portion of a stream that receives some water from groundwater discharge because the stream's elevation is below the groundwater table. (Compare Influent stream.)

ELASTIC REBOUND THEORY: A theory of fault movement and earthquake generation holding that faults remain locked while strain energy accumulates in the rock formations on both sides, temporarily deforming them until a sudden slip along the fault releases the energy.

ELECTRON: A negatively charged atomic particle with a negligible mass (9.1 3 10²²⁸ gram) and a charge of 21.6 3 10²¹⁹ coulomb, commonly expressed as 21. The position of an electron about an atomic nucleus is not fixed but is described as a region where an electron is most likely to be found.

ELEVATION: The vertical height of one point on the Earth above a given plane, usually sea level.

EOLIAN: Pertaining to or deposited by wind.

EON: The largest division of geologic time, embracing several eras; for example, the Phanerozoic eon, from 600 million years ago to the present.

EPEIROGENY: Large-scale, primarily vertical, movement of the crust, characteristically so gradual that rocks are little folded and faulted.

EPICENTER: The point on the Earth's surface directly above the focus of an earthquake.

EPOCH: A subdivision of a geologic period, often chosen to correspond to a stratigraphic sequence. Also used for a division of time corresponding to a paleomagnetic interval.

ERA: A division of geologic time including several periods, but smaller than an eon. Commonly recognized eras are Precambrian, Paleozoic, Mesozoic, and Cenozoic.

ERG: Extensive region, or "sea," of composite dunes formed by wind-transported sand and found in major deserts.

EROSION: The set of all processes by which soil and rock are loosened and moved downhill or downwind.

ERRATIC: Rock fragment (especially boulder-sized) carried by a glacier away from the outcrop from which it was derived, often into an area underlain by a rock type different from that of the rock fragment.

ESKER: A glacial deposit of sand and gravel in the form of a continuous, winding ridge, formed from the deposits of a stream flowing beneath the ice.

ESTUARY: A body of water along a coastline, open to the ocean but diluted by fresh water.

EXCLUSIVE ECONOMIC ZONE: The zone from a country's coast to 200 miles offshore in which the country has exclusive rights to mineral deposits.

EXFOLIATION: A physical weathering process in which sheets of rock are fractured and detached from an outcrop.

EXTRUSIVE IGNEOUS ROCK: An igneous rock formed from lava or from other products of volcanic material spewed out onto the surface of the Earth.