Science / Geology Glossary

Dry Wash: An intermittent streambed in an arroyo or canyon that carries water only briefly after a rain.

Dry-Hole: A well drilled in hopes of finding oil or natural gas that fails to make commercial production rates.

Dry-Hole Contribution: A payment made to the owner of an unsuccessful well in exchange for a log of the well and evaluation data.

Dune: A mound or ridge of wind-blown sand. Typically found in deserts and inland from a beach. Many dunes are moved by the wind.

Earthflow: A detached mass of soil that moves downslope over a curved failure surface under the influence of gravity. An earthflow is more complex than a slump: it has a higher moisture content and the . . . View Full Definition

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

Ebb Tide: A tidal current that generally moves seaward and occurs during the part of the tide cycle when sea level is falling.

Echo-Sounder: An oceanographic instrument that emits sound pulses into the water and measures its depth by the time elapsed before they return.

Ecliptic: The plane that contains the Earth's orbit around the Sun.

Eclogite: An extremely high-pressure metamorphic rock containing garnet and pyroxene.

Ecology: The science of the life cycles, populations, and interactions of various biological species as controlled by their physical environment, including also the effect of life forms upon the environment.

Effluent Stream: A stream that gains water from ground water flow. These streams are typical of humid climates where water tables are high. The discharge of an effluent stream can be sustained by ground wate . . . View Full Definition

Elastic Limit: The maximum stress that can be applied to a body without resulting in permanent deformation - the rock reverts to its original shape after the stress is removed. In the case of a fault or a . . . View Full Definition

Elastic Rebound Theory: A theory that explains the earthquake process. In this theory, slowly accumulating elastic strain builds within a rock mass over an extended length of time. This strain is suddenly released . . . View Full Definition

Electron: A subatomic particle with a negative charge and of negligible mass that orbits the nucleus of an atom.

Elevation: The vertical distance between mean sea level and a point or object on, above or below Earth's surface.

Elliptical Orbit: An orbit with the shape of a geometrical ellipse. All orbits are elliptical or hyperbolic, with the Sun occupying one focus.

Eolian: A term used in reference to the wind. Eolian materials or structures are deposited by or created by the wind.

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