Earthflow – Detachment of soil and broken rock and its subsequent downslope movement at slow or moderate rates in a stream.
Earthquake – 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 – Part of the tide cycle during which the water level is falling.
Echo-Sounder – Oceanographic instrument that emits sound pulses into the water and measures its depth by the time elapsed before they return.
Ecliptic – Plane that contains the Earth’s orbit around the Sun.
Eclogite – Extremely high-pressure metamorphic rock containing garnet and pyroxene.
Ecology – 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.
Effective Porosity – Amount of interconnected pore space through which fluids can pass. Effective porosity is usually less than total porosity because some dead-end pores may be occupied by static fluid.
Elastic Limit – Maximum stress that can be applied to a body without resulting in permanent strain.
Elastic Moduli – Elastic moduli or Elastic Constants specify the stress- strain properties of isotropic materials in which stress is proportional to strain. They include bulk and shear moduli.
Elastic Rebound Theory – Theory of fault movement and earthquake generation that holds that faults remain locked while strain energy accumulates in the country rock, and then suddenly slip and release this energy.
Electric Field – Vector field describing the force on a unit electrical ge [newtons/coulomb = volts/meter].
Electrical Logs – Provide information on porosity, hydraulic conductivity, and fluid content of formations drilled in fluid-filled boreholes. This record is based on the dielectric properties of the aquifer materials measured by geophysical devices lowered down boreholes or wells.
Electrode – Piece of metallic material that acts as an electric contact with a non-metal. In chemistry, it refers to an instrument designed to measure an electrical response that is proportional to the condition being assessed.
Electromagnetic-Casing Inspection Log – Effects of eddy currents on a magnetic field are used to provide a record of the thickness of the casing wall.
Electromagnetic Method – Method which measures magnetic and/or electric fields associated with subsurface currents.
Electron – Negatively charged particle with negligible mass orbiting around the nucleus of an atom.
Electron Volt – Energy acquired by an electron passing through a potential difference of one volt (eV); used for measuring the energy of nuclear radiation and particles, usually expressed as million electron volts (MeV).
Electrowinning – Electrochemical process in which a metal dissolved within an electrolyte is plated onto an electrode. Used to recover metals such as cobalt, copper, gold and nickel from solution in the leaching of ores, concentrates, precipitates and matte.
Elevation – Vertical height of one point on the Earth above a given datum plane, usually sea level.
Elliptical Orbit – Orbit with the shape of a geometrical ellipse. All orbits are elliptical or hyperbolic, with the Sun occupying one focus.
Enargite – Rare copper mineral that is related to the rare mineral wurtzite. Wurtzite is a zinc sulfide with a formula of ZnS. In enargite 75% of the zinc atoms are replaced by copper and 25% of the zinc atoms are replaced by arsenic, and produce the formula Cu3AsS4.
Enriched – Containing higher than normal amounts.
EIA – Environmental Impact Assessment Report.
Environmental Impact Study – Written report, compiled prior to a production decision that examines the effects proposed mining activities will have on the natural surroundings.
Eocene Epoch – An epoch from 54.8 to 33.9 million years ago comprised of four Ages: the Ypresian, Lutetian, Bartonian, and Priabonian Ages.
Eolian – Pertaining to or deposited by wind.
Eon – Primary division of geologic time lasting over 500 million years, four of which have been defined: Hadean, Archean, Proterozoic, and Phanerozoic. Eons are divided into Eras, which are in turn divided into Periods, Epochs and Ages.
Epeirogeny – Uplift or depression of the Earth’s crust, affecting large areas of land or ocean bottom.
Epicenter – Point on the Earth’s surface directly above the incident of an Earthquake.
Epidote – Greenish-yellow mineral consisting of calcium, aluminum, iron and silica. Common in metamorphic rocks, especially as a coating on joint surfaces.
Epigenetic – Processes that act after formation of a rock unit.
Epithermal – Hydrothermal deposit formed close to surface at low temperature and pressure.
Epithermal Neutron – Neutron source emits fast neutrons that are slowed by moderation to an energy level just above thermal equilibrium, where they are available for capture. Most modern neutron probes can measure epithermal neutrons, because they are less affected by chemical composition than thermal neutrons.
Epoch – Division of geologic time lasting tens of millions of years. Epochs are subdivisions of geologic periods, often chosen to correspond to a stratigraphic series. They are used for a division of time corresponding to a paleomagnetic interval.
Equipotential Map – Plot in which points of equal hydraulic head are connected.
Era – Division of geologic time of several hundred million years duration. An era is smaller than an eon and longer than a period. The commonly recognized eras of the Phanerozoic Eon are the Paleozoic, Mesozoic, and Cenozoic eras.
Erosion – Processes that break up or wear down rocks or unconsolidated sediment and moves them from one place to another; the forces of erosion include water, ice, wind and gravity. They are commonly moved downhill or downwind.
Erratic – A large boulder carried by glacial ice to an area removed from its point of origin. It is left behind when the ice melts.
Escarpment – Steep or vertical cliff, either above or below sea level.
Esker – Narrow ridge of glacial sediment deposited by a stream flowing in and under a melting glacier or ice sheet.
Estuary – Area where fresh water comes into contact with seawater, usually in a partly enclosed coastal body of water. A mix of fresh and salt water where the current of a stream meets the tidal waters.
Eugeosyncline – Seaward part of a geosyncline; characterized by clastic sediments and volcanism.
Eustatic Change – Sea level changes that affect the whole Earth.
Eutrophication – Superabundance of algal life in a body of water; caused by an unusual influx of nitrate, phosphate, or other nutrients.
Evaporite – Chemical sedimentary rock consisting of minerals precipitated by evaporating waters, especially salt and gypsum.
Exfoliation – Physical weathering process in which sheets of rock are fractured and detached from an outcrop.
Exobiology – Study of life outside the Earth.
Exploration – Prospecting, sampling, mapping, diamond drilling and other work involved in searching for ore.
Exploration Information – Geological, geophysical, geochemical, sampling, drilling, trenching, analytical testing, assaying, mineralogical, and metallurgical and other similar information concerning a particular property that is derived from activities undertaken to locate, investigate, define or delineate a mineral prospect or mineral deposit.
Extinction Angle – Angle between a crystallographic direction, such as a face or cleavage plane, and the direction in which all light is blocked by a pair of crossed polarizers
Extrusive – Rocks that form on the surface from molten lava. The opposite of an intrusive.
Extrusive Rock – Rock formed from magma that has erupted explosively or has flowed onto the earth’s surface from a volcano.