Glossary of Terms: E

Earth Albedo

Is the reflectivity of the Earth's atmosphere and surface combined. Measurements indicate that the average Earth albedo is approximately 30%.

 

Earthflow

A rapid type of downslope mass movement that involves soil and other loose sediments. Usually triggered by water saturation from rainfall.

 

Earthquake

Is a sudden motion or trembling in the Earth. The motion is caused by the quick release of slowly accumulated energy in the form of seismic waves. Most earthquakes are produced along faults, tectonic plate boundaries, or along the mid-oceanic ridges.

 

Earthquake Focus

Point of stress release in an earthquake.

 

Earth Revolution

Refers to the orbit of the Earth around the Sun. This celestial motion takes 365 1/4 days to complete one cycle. Further, the Earth's orbit around the Sun is not circular, but elliptical.

 

Earth Rotation

Refers to the spinning of the Earth on its polar axis.

 

Earth Sciences Tradition

Academic tradition in modern Geography that investigates natural phenomena from a spatial perspective.

 

Easterly Wave

Atmospheric disturbance in the tropical trade winds. Occasionally these systems intensify into hurricanes.

 

Easting

First measurement of a grid reference used to specific the location of a point on a rectangular coordinate system. The distance measured eastward from the origin of a rectangular coordinate system.

 

Ebb Tide

Time during the tidal period when the tide is falling. Compare with flood tide.

 

Eccentricity

Geometric shape of the Earth's orbit. This shape varies from being elliptical to almost circular.

 

Ecological Diversity

See ecosystem diversity.

 

Ecological Niche

Is all of the physical, chemical and biological conditions required by a species for survival, growth and reproduction. Two further abstractions of this concept are the fundamental niche and the realized niche.

 

Ecology

The study of the factors that influence the distribution and abundance of species.

 

Ecosphere

See biosphere.

 

Ecosystem

An ecosystem is a system where populations of species group together into communities and interact with each other and the abiotic environment.

 

Ecosystem Diversity

The variety of unique biological communities found on the Earth. A component of biodiversity. Also see genetic diversity and species diversity.

 

Ecotone

Boundary zone between two unique community types.

 

Eddy

A localized chaotic movement of air or liquid in a generally uniform larger flow.

 

Eddy Diffusion

Mixing of the atmosphere by chaotic air currents.

 

Edge Wave

A wave of water that moves parallel to the shore. This wave is usually a secondary wave of complex formation.

 

Effusive Eruption

Volcanic eruption where low-viscosity basaltic magma is released. This type of eruption is not explosive and tends to form shield volcanoes.

 

Elastic Deformation

Change in the shape of a material as the result of the force of compression or expansion. Upon release of the force, the material returns to its original shape. Also called plastic deformation.

 

Elastic Limit

Maximum level of elastic deformation of a material without rupture.

 

Elastic Rebound Theory

Theory that describes how earthquakes arise from the horizontal movement of adjacent tectonic plates along a linear strike-slip fault. This theory suggests that the two plates moving in opposite directions become locked for some period of time because of friction. However, the accumulating stress overcomes the friction and causes the plate to suddenly move over a short time period which generates an earthquake.

 

Elastic Wave

An energy wave that causes elastic deformation in a material without its structure and shape being deformed.

 

Electrical Energy

Energy produced from the force between two objects having the physical property of electrical charge.

 

Electromagnetic Energy

Energy stored in electromagnetic waves or radiation. Energy is released when the waves are absorbed by a surface. Any object with a temperature above absolute zero (-273° Celsius) emits this type of energy. The intensity of energy released is a function of the temperature of the radiating surface. The higher the temperature the greater the quantity of energy released.

 

Electromagnetic Radiation (Waves)

Emission of energy in the form of electromagnetic waves. All objects above the temperature of absolute zero (-273.15° Celsius) radiate energy to their surrounding environment. The amount of electromagnetic radiation emitted by a body is proportionally related to its temperature.

 

Electromagnetic Spectrum

See spectrum.

 

Electron

A sub-particle of an atom that contains a negative atomic charge.

 

Element

A molecule composed of one type of atom. Chemists have recognized or created 112 different types of elements. See the following WWW link for the chemical description of these different elements. Two or more different elements form a compound.

 

El Niño

Name given to the occasional development of warm ocean surface waters along the coast of Ecuador and Peru. When this warming occurs the tropical Pacific trade winds weaken and the usual upwelling of cold, nutrient rich deep ocean water off the coast of Ecuador and Peru is reduced. The El Niño normally occurs around Christmas and lasts usually for a few weeks to a few months. Sometimes an extremely warm event can develop that lasts for much longer time periods.

 

Eluviation

Movement of humus, chemical substances, and mineral particles from the upper layers of a soil to lower layers by the downward movement of water through the soil profile. Compare with illuviation.

 

Emigration

Migration of an organism out of an area for the purpose of changing its residence permanently. Compare with immigration.

 

Emissivity

The ratio of total radiative output from a body per unit time per unit area at a specific temperature and wavelength to that of a black body under the same environmental conditions.

 

Endangered Species

A species found in nature that has so few surviving individuals that the it could soon become extinct in all or most of its natural range. Also see threatened species.

 

Endogenic

Refers to a system that is internal to the Earth.

 

Energy

Is defined as the capacity for doing work. Energy can exist the following forms: radiation; kinetic energy; potential energy; chemical energy; atomic energy; electromagnetic energy; electrical energy; and heat energy.

 

Energy Flux

The rate of energy flow from, into, or through a substance.

 

Entisols

Soil order (type) of the United States Natural Resources Conservation Service Soil Classification System. Soil of recent development with no or poorly developed soil horizons.

 

Entrainment

One of three distinct processes involved in erosion. More specifically, it is the process of particle lifting by an agent of erosion.

 

Entropy

Entropy is the measure of the disorder or randomness of energy and matter in a system.

 

Environment

(1) Abiotic and biotic factors that influence the life of an organism.

(2) Abiotic and biotic factors that influence the function of some nonliving natural system.

 

Environmental Gradient

Spatial gradient where abiotic and biotic factors vary.

 

Environmental Lapse Rate (ELR)

The rate of air temperature increase or decrease with altitude. The average ELR in the troposphere is an air temperature decrease of 6.5° Celsius per 1000 meters rise in elevation.

 

Environmental Science

Field of knowledge that studies how humans and other species interact with one another and with the nonliving environment. It is both a physical and social science that integrates knowledge from a wide range of disciplines, including physics, chemistry, biology, geology, geography, economics, political science, sociology, psychology, and philosophy.

 

Environmental System

A system where life interacts with the various abiotic components found in the atmosphere, hydrosphere, and lithosphere.

 

Enzyme

Are types of proteins that are used to facilitate and regulate chemical reactions within cells.

 

Eolian

Geomorphic process involving wind. Alternative spelling aeolian.

 

Eolian Landform

Is a landform formed from the erosion or deposition of weathered surface materials by wind. This includes landforms with some of the following geomorphic features: sand dunes, deflation hollows, and desert pavement. Alternative spelling aeolian landform.

 

Eon

Longest geologic time unit.

 

Epicenter

Surface location of an earthquake's focus.

 

Epiphyte

Type of vegetation that gets its physical support from the branches of other plants. Commonly found in the tropical forests.

 

Epoch

Geologic time unit that is shorter than a period.

 

Equator

Location on the Earth that has a latitude of 0°.

 

Equilibrium

Equilibrium describes the average condition of a system, as measured through one of its elements or attributes, over a specific period of time.

 

Equinox

Two days during the year when the declination of the Sun is at the equator. The September equinox occurs on September 22 or 23. The March equinox occurs on March 20 or 21. On these days, all locations on our planet (except the poles) experience equal (12 hour) day and night.

 

Era

Geologic time unit that is shorter than an eon but longer than a period.

 

Erg Desert

A region in a desert where sand is very abundant.

 

Erosion

The removal of weathered sediment or rocks by the forces of wind, water, and ice.

 

Erosional Landform

Is a landform formed from the removal of weathered and eroded surface materials by wind, water, glaciers, and gravity. This includes landforms with some of the following geomorphic features: river valleys, glacial valleys, and coastal cliffs.

 

Erratic

A large rock boulder that has been transported by glaciers away from its origin and deposited in a region of dissimilar rock.

 

Esker

Long twisting ridges of sand and gravel found on the Earth's surface. Created when the deposits of subsurface glacial streams are placed on the ground after glacial melting.

 

Establishment

Subsequent growth and/or reproduction of a colonized species in a new territory.

 

Estimator

An estimator is any value calculated from the sample data For example, the sample mean is an estimator of the population mean.

 

Estuary

Somewhat enclosed coastal area at the mouth of a river where nutrient rich fresh water meets with salty ocean water.

 

Eukaryota

All the organisms with a eukaryote cell type. This group includes animals, plants, fungi, and protists.

 

Eukaryote

Organisms whose cells have a membrane-bound nucleus and many specialized structures located within their cell boundary. In these organisms, genetic material is organized into chromosomes that reside in the nucleus.

 

Eustacy

Variations in sea-level that are related to changes in the volume of seawater in the oceans.

 

Eutrophication

Physical, chemical and biological changes in a water body as a result of the input nitrogen and phosphorus.

 

Eutrophic Lake

Lake that has an excessive supply of nutrients, mostly in the form of nitrates and phosphates. Also see mesotrophic lake and oligotrophic lake.

 

Evaporation

Evaporation can be defined as the process by which liquid water is converted into a gaseous state. Evaporation can only occur when water is available. It also requires that the humidity of the atmosphere be less than the evaporating surface (at 100% relative humidity there is no more evaporation). The evaporation process requires large amounts of energy. For example, the evaporation of one gram of water at a temperature of 100° Celsius requires 540 calories of heat energy (600 calories at 0° Celsius).

 

Evaporation Fog

A type of fog produced from the advection of cold air over warm water or warm or moist land. This type of fog is sometimes called steam fog or sea smoke.

 

Evaporation Pan

Meteorological instrument that is used to measure evaporation rates.

 

Evaporite

Type of sedimentary rock that is formed from the concentration of dissolved salts through evaporation.

 

Evapotranspiration

Combined loss of water to the atmosphere via the processes of evaporation and transpiration.

 

Evergreen Vegetation

Vegetation that keeps a majority of their leaves or needles throughout the year. Also see deciduous vegetation and succulent vegetation.

 

Evolution

Is a process by which species come to possess genetic adaptations to their environment. Its mechanism is natural selection. It also requires genetic mutations.

 

Exfoliation Dome

A physical weathering feature associated with granite that is the result of the erosion of overburden material and pressure-release. With the release of pressure, layers of rock break off in sheets or shells leaving a dome-like bedrock feature.

 

Exogenic

Refers to a system that is external to the Earth.

 

Exosphere

The outermost zone in the Earth's atmosphere. This layer has an altitude greater than 480 kilometers and is primarily composed of hydrogen and helium gas.

 

Exotic Stream

A stream that has a course that begins in a humid climate and end in an arid climate. Because of reductions in precipitation and and increases in evaporation, the discharge of these streams deceases downslope. Examples of such streams are the Nile and Colorado Rivers.

 

Experiment

A controlled investigation designed to evaluate the outcomes of causal manipulations on some system of interest.

 

Exploitation

Form of competition where the indirect effects of the two or more species or individuals reduce the supply of the limiting resource or resources needed for survival.

 

Explosive Eruption

Volcanic eruption where high-viscosity granite-rich magma causes an explosion of ash and pyroclastic material. This type of eruption is common to composite and caldera volcanoes.

 

Extinction

Disappearance of a species from all or part of their geographic range. Also see background extinction and mass extinction.

 

Extrusive Igneous Rock

Igneous rock that forms on the surface of the Earth. Also called volcanic igneous rock.

 

Eye

Area in the center of a hurricane that is devoid of clouds.

 

 

Citation: Pidwirny, M. (2006). "Glossary of Terms: E". Fundamentals of Physical Geography, 2nd Edition. Date Viewed. http://www.physicalgeography.net/physgeoglos/e.html