temperatures and confining
pressures are high.
Dune A hill or ridge of
wind-deposited sand.
Earthflow The downslope
movement of water-saturated,
clay-rich sediment, most
characteristic of humid regions.
Earthquake The vibration of
Earth produced by the rapid release
of energy.
Echo sounder An instrument
used to determine the depth of
water by measuring the time
interval between emission of a
sound signal and the return of its
echo from the bottom.
Elastic deformation
Nonpermanent deformation in
which rock returns to its original
shape when the stress is released.
Elastic rebound The sudden
release of stored strain in rocks that
results in movement along a fault.
Electron A negatively charged
subatomic particle that has a
negligible mass and is found outside
the atom’ s nucleus.
Element A substance that cannot
be decomposed into simpler
substances by ordinary chemical or
physical means.
Eluviation The washing out of
fine soil components from the A
horizon by downward-percolating
water.
Emergent coast A coast where
land formerly below the sea level
has been exposed by either crustal
uplift or a drop in sea level or both.
End moraine A ridge of till
marking a former position of the
front of the glacier.
Energy levels Spherically shaped
negatively charged zones that
surround the nucleus of an atom.
Eon The largest time unit on the
geologic time scale, next in order of
magnitude above era.
Epicenter The location on Earth’ s
surface that lies directly above the
focus of an earthquake.
Epoch A unit of the geological
time scale that is a subdivision of a
period.
Era A major division on the
geologic time scale; eras are divided
into shorter units called periods.
Erosion The incorporation and
transportation of material by a
mobile agent, such as water, wind,
or ice.
Eruption column Buoyant
plumes of hot ash-laden gases that
can extend thousands of meters into
the atmosphere.
Esker Sinuous ridge composed
largely of sand gravel deposited
by a stream flowing in a tunnel
beneath a glacier near its
terminus.
Estuary A partially enclosed
coastal water body that is connected
to the ocean. Salinity here is
measurably reduced by the
freshwater flow of rivers.
Eukaryotes Organisms whose
genetic material is enclosed in a
nucleus. Plants, animals, and fungi
are eukaryotes.
Evaporite A sedimentary rock
formed of material deposited from
solution by evaporation of water.
Evapotranspiration The
combined effect of evaporation and
transpiration.
Exfoliation dome Large,
dome-shaped structure, usually
composed of granite, formed by
sheeting.
Exotic stream A permanent
stream that traverses a desert and
has its source in well-watered areas
outside the desert.
External process Process such as
weathering, mass wasting, or
erosion that is powered by the Sun
and transforms solid rock into
sediment.
Extrusive Igneous activity that
occurs at Earth’ s surface.
Eye A zone of scattered clouds
and calm averaging about 20
kilometers in diameter at the center
of a hurricane.
Eye wall A doughnut-shaped area
of intense cumulonimbus
(thunderstorm) development and
very strong winds that surrounds
the eye of a hurricane.
Fall A type of movement
common to mass-wasting processes
that refers to the free falling of
detached individual pieces of any
size.
Fault A break in a rock mass
along which movement has
occurred.
Fault creep Slow, gradual
displacement along a fault that
occurs relatively smoothly and with
little noticeable seismic activity.
Fault scarp A cliff created by
movement along a fault. It
represents the exposed surface of
the fault prior to modification by
weathering and erosion.
Fault-block mountain A
mountain formed by the
displacement of rock along a fault.
Felsic A term derived from
feldspar and silica (quartz). It is a
term used to describe granitic
igneous rocks.
Ferromagnesian silicate See
Dark silicate.
Fetch The distance that the wind
has traveled across the open water.
Fine-grained texture See
Aphanitic texture.
Fiord A steep-sided inlet of the
sea formed when a glacial trough
was partially submerged.
Fissure A crack in rock along
which there is a distinct separation.
Fissure eruption An eruption in
which lava is extruded from narrow
fractures or cracks in the crust.
Flood The overflow of a stream
channel that occurs when discharge
exceeds the channel’ s capacity. The
most common and destructive
geologic hazard.
Flood basalts Flows of basaltic
lava that issue from numerous
cracks or fissures and commonly
cover extensive areas to thicknesses
of hundreds of meters.
Floodplain The flat, low-lying
portion of a stream valley subject to
periodic inundation.
Flow A type of movement
common to mass-wasting processes
in which water-saturated material
moves downslope as a viscous fluid.
Fluorescence The absorption of
ultraviolet light, which is reemitted
as visible light.
Focus (earthquake) The zone
within Earth where rock
displacement produces an
earthquake.
Fold A bent layer or series of
layers that were originally horizontal
and subsequently deformed.
Foliated A texture of
metamorphic rocks that gives the
rock a layered appearance.
Foliation A term for a linear
arrangement of textural features
often exhibited by metamorphic
rocks.
Foreset bed An inclined bed
deposited along the front of a delta.
Foreshocks Small earthquakes
that often precede a major
earthquake.
Foreshore That portion of the
shore lying between the normal
high- and low-water marks; the
intertidal zone.
Fossil The remains or traces of
organisms preserved from the
geologic past.
Fossil fuel General term for any
hydrocarbon that may be used as a
fuel, including coal, oil, natural gas,
bitumen from tar sands, and shale
oil.
Fossil magnetism See
Paleomagnetism.
Fossil succession Fossil
organisms succeed one another in a
definite and determinable order, and
any time period can be recognized
by its fossil content.
Fractional crystallization The
process that separates magma into
components having varied
compositions and melting points.
Fracture (mineral) One of the
basic physical properties of
minerals. It relates to the breakage
of minerals when there are no
planes of weakness in the
crystalline structure. Examples
include conchoidal, irregular, and
splintery.
Fracture (rock) Any break or
rupture in rock along which no
appreciable movement has taken
place.
Fracture zone Linear zone of
irregular topography on the
deep-ocean floor; it follows
transform faults and their inactive
extensions.
Fragmental texture See
Pyroclastic texture.
Frost wedging The mechanical
breakup of rock caused by the
expansion of freezing water in
cracks and crevices.
Fumarole A vent in a volcanic
area from which fumes or gases
escape.
Gaining stream Streams that gain
water from the inflow of
groundwater through the
streambed.
GLOSSARY
536
pressures are high.
Dune A hill or ridge of
wind-deposited sand.
Earthflow The downslope
movement of water-saturated,
clay-rich sediment, most
characteristic of humid regions.
Earthquake The vibration of
Earth produced by the rapid release
of energy.
Echo sounder An instrument
used to determine the depth of
water by measuring the time
interval between emission of a
sound signal and the return of its
echo from the bottom.
Elastic deformation
Nonpermanent deformation in
which rock returns to its original
shape when the stress is released.
Elastic rebound The sudden
release of stored strain in rocks that
results in movement along a fault.
Electron A negatively charged
subatomic particle that has a
negligible mass and is found outside
the atom’ s nucleus.
Element A substance that cannot
be decomposed into simpler
substances by ordinary chemical or
physical means.
Eluviation The washing out of
fine soil components from the A
horizon by downward-percolating
water.
Emergent coast A coast where
land formerly below the sea level
has been exposed by either crustal
uplift or a drop in sea level or both.
End moraine A ridge of till
marking a former position of the
front of the glacier.
Energy levels Spherically shaped
negatively charged zones that
surround the nucleus of an atom.
Eon The largest time unit on the
geologic time scale, next in order of
magnitude above era.
Epicenter The location on Earth’ s
surface that lies directly above the
focus of an earthquake.
Epoch A unit of the geological
time scale that is a subdivision of a
period.
Era A major division on the
geologic time scale; eras are divided
into shorter units called periods.
Erosion The incorporation and
transportation of material by a
mobile agent, such as water, wind,
or ice.
Eruption column Buoyant
plumes of hot ash-laden gases that
can extend thousands of meters into
the atmosphere.
Esker Sinuous ridge composed
largely of sand gravel deposited
by a stream flowing in a tunnel
beneath a glacier near its
terminus.
Estuary A partially enclosed
coastal water body that is connected
to the ocean. Salinity here is
measurably reduced by the
freshwater flow of rivers.
Eukaryotes Organisms whose
genetic material is enclosed in a
nucleus. Plants, animals, and fungi
are eukaryotes.
Evaporite A sedimentary rock
formed of material deposited from
solution by evaporation of water.
Evapotranspiration The
combined effect of evaporation and
transpiration.
Exfoliation dome Large,
dome-shaped structure, usually
composed of granite, formed by
sheeting.
Exotic stream A permanent
stream that traverses a desert and
has its source in well-watered areas
outside the desert.
External process Process such as
weathering, mass wasting, or
erosion that is powered by the Sun
and transforms solid rock into
sediment.
Extrusive Igneous activity that
occurs at Earth’ s surface.
Eye A zone of scattered clouds
and calm averaging about 20
kilometers in diameter at the center
of a hurricane.
Eye wall A doughnut-shaped area
of intense cumulonimbus
(thunderstorm) development and
very strong winds that surrounds
the eye of a hurricane.
Fall A type of movement
common to mass-wasting processes
that refers to the free falling of
detached individual pieces of any
size.
Fault A break in a rock mass
along which movement has
occurred.
Fault creep Slow, gradual
displacement along a fault that
occurs relatively smoothly and with
little noticeable seismic activity.
Fault scarp A cliff created by
movement along a fault. It
represents the exposed surface of
the fault prior to modification by
weathering and erosion.
Fault-block mountain A
mountain formed by the
displacement of rock along a fault.
Felsic A term derived from
feldspar and silica (quartz). It is a
term used to describe granitic
igneous rocks.
Ferromagnesian silicate See
Dark silicate.
Fetch The distance that the wind
has traveled across the open water.
Fine-grained texture See
Aphanitic texture.
Fiord A steep-sided inlet of the
sea formed when a glacial trough
was partially submerged.
Fissure A crack in rock along
which there is a distinct separation.
Fissure eruption An eruption in
which lava is extruded from narrow
fractures or cracks in the crust.
Flood The overflow of a stream
channel that occurs when discharge
exceeds the channel’ s capacity. The
most common and destructive
geologic hazard.
Flood basalts Flows of basaltic
lava that issue from numerous
cracks or fissures and commonly
cover extensive areas to thicknesses
of hundreds of meters.
Floodplain The flat, low-lying
portion of a stream valley subject to
periodic inundation.
Flow A type of movement
common to mass-wasting processes
in which water-saturated material
moves downslope as a viscous fluid.
Fluorescence The absorption of
ultraviolet light, which is reemitted
as visible light.
Focus (earthquake) The zone
within Earth where rock
displacement produces an
earthquake.
Fold A bent layer or series of
layers that were originally horizontal
and subsequently deformed.
Foliated A texture of
metamorphic rocks that gives the
rock a layered appearance.
Foliation A term for a linear
arrangement of textural features
often exhibited by metamorphic
rocks.
Foreset bed An inclined bed
deposited along the front of a delta.
Foreshocks Small earthquakes
that often precede a major
earthquake.
Foreshore That portion of the
shore lying between the normal
high- and low-water marks; the
intertidal zone.
Fossil The remains or traces of
organisms preserved from the
geologic past.
Fossil fuel General term for any
hydrocarbon that may be used as a
fuel, including coal, oil, natural gas,
bitumen from tar sands, and shale
oil.
Fossil magnetism See
Paleomagnetism.
Fossil succession Fossil
organisms succeed one another in a
definite and determinable order, and
any time period can be recognized
by its fossil content.
Fractional crystallization The
process that separates magma into
components having varied
compositions and melting points.
Fracture (mineral) One of the
basic physical properties of
minerals. It relates to the breakage
of minerals when there are no
planes of weakness in the
crystalline structure. Examples
include conchoidal, irregular, and
splintery.
Fracture (rock) Any break or
rupture in rock along which no
appreciable movement has taken
place.
Fracture zone Linear zone of
irregular topography on the
deep-ocean floor; it follows
transform faults and their inactive
extensions.
Fragmental texture See
Pyroclastic texture.
Frost wedging The mechanical
breakup of rock caused by the
expansion of freezing water in
cracks and crevices.
Fumarole A vent in a volcanic
area from which fumes or gases
escape.
Gaining stream Streams that gain
water from the inflow of
groundwater through the
streambed.
GLOSSARY
536