Supernova An exploding star that
increases its brightness many
thousands of times.
Superposition, law of In any
undeformed sequence of
sedimentary rocks, each bed is older
than the one above and younger
than the one below.
Surf A collective term for
breakers; also the wave activity in
the area between the shoreline and
the outer limit of breakers.
Surface soil The upper portion of
a soil profile consisting of the O and
A horizons.
Surface waves Seismic waves
that travel along the outer layer of
Earth.
Surge A period of rapid glacial
advance; surges are typically
sporadic and short-lived.
Suspended load The fine
sediment carried within the body of
flowing water or air.
Swells Wind-generated waves
that have moved into an area of
weaker winds or calm.
Syncline A linear downfold in
sedimentary strata; the opposite of
anticline.
System A group of interacting or
interdependent parts that form a
complex whole.
Tablemount See Guyot.
Tabular Describing a feature such
as an igneous pluton having two
dimensions that are much longer
than the third.
Talus An accumulation of rock
debris at the base of a cliff.
Tarn A small lake in a cirque.
Tectonic plate See Lithospheric
plate.
Tectonics The study of the
large-scale processes that collectively
deform Earth’ s crust.
Temporary (local) base level
The level of a lake, resistant rock
layer, or any other base level that
stands above sea level.
Tenacity Describes a mineral’ s
toughness or its resistance to
breaking or deforming.
Terminal moraine The end
moraine marking the farthest
advance of a glacier.
Terrace A flat, benchlike structure
produced by a stream that was left
elevated as the stream cut
downward.
Terrane A crustal block bounded
by faults whose geologic history is
distinct from the histories of
adjoining crustal blocks.
Terrigenous sediment Seafloor
sediment derived from terrestrial
weathering and erosion.
Texture The size, shape, and
distribution of the particles that
collectively constitute a rock.
Theory A well-tested and widely
accepted view that explains certain
observable facts.
Thermal metamorphism See
Contact metamorphism.
Thrust fault A low-angle reverse
fault.
Tide Periodic change in the
elevation of the ocean’ s surface.
Till Unsorted sediment deposited
directly by a glacier.
Tillite A rock formed when glacial
till is lithified.
Tombolo A ridge of sand that
connects an island to the mainland
or to another island.
Topset bed An essentially
horizontal sedimentary layer
deposited on top of a delta during
floodstage.
Transform fault A major
strike-slip fault that cuts through the
lithosphere and accommodates
motion between two plates.
Transform fault boundary A
boundary in which two plates slide
past one another without creating or
destroying lithosphere.
Transpiration The release of
water vapor to the atmosphere by
plants.
Transported soil Soils that form
on unconsolidated deposits.
Transverse dunes A series of long
ridges oriented at right angles to the
prevailing wind; these dunes form
where vegetation is sparse and sand
is very plentiful.
Travertine A form of limestone
that is deposited by hot springs or as
a cave deposit.
Trellis drainage A system of
streams in which nearly parallel
tributaries occupy valleys cut in
folded strata.
Trench An elongate depression in
the seafloor produced by bending of
oceanic crust during subduction.
Tsunami The Japanese word for a
seismic sea wave.
Turbidite Turbidity current
deposit characterized by graded
bedding.
Turbidity current A downslope
movement of dense, sediment-laden
water created when sand and mud
on the continental shelf and slope
are dislodged and thrown into
suspension.
Turbulent flow The movement of
water in an erratic fashion often
characterized by swirling,
whirlpool-like eddies. Most
streamflow is of this type.
Ultimate base level Sea level; the
lowest level to which stream erosion
could lower the land.
Ultramafic Compositional
category for igneous rocks made up
almost entirely of ferromagnesian
minerals (mostly olivine and
pyroxene).
Unconformity A surface that
represents a break in the rock
record; caused by erosion or
nondeposition.
Uniformitarianism The concept
that the processes that have shaped
Earth in the geologic past are
essentially the same as those
operating today.
Unsaturated zone The area
above the water table where
openings in soil, sediment, and rock
are not saturated with water but
filled mostly with air.
Valence electron The electrons
involved in the bonding process; the
electrons occupying the highest
principal energy level of an atom.
Valley glacier A glacier confined
to a mountain valley, which in most
instances had previously been a
stream valley.
Valley train A relatively narrow
body of stratified drift deposited on
a valley floor by meltwater streams
that issue from the terminus of a
valley glacier.
Vein deposit A mineral filling a
fracture or fault in a host rock. Such
deposits have a sheetlike, or tabular,
form.
Ventifact A cobble or pebble
polished and shaped by the
sandblasting effect of wind.
Vesicles Spherical or elongated
openings on the outer portion of a
lava flow that were created by
escaping gases.
Vesicular texture A term applied
to aphanitic igneous rocks that
contain many small cavities, called
vesicles.
Viscosity A measure of a fluid’ s
resistance to flow.
Volatiles Gaseous components
of magma dissolved in the
melt. Volatiles will readily
vaporize (form a gas) at surface
pressures.
Volcanic Pertaining to the
activities, structures, or rock types of
a volcano.
Volcanic bomb A streamlined
pyroclastic fragment ejected from a
volcano while the fragment is still
molten.
Volcanic island arc A chain of
volcanic islands generally located a
few hundred kilometers from a
trench where there is active
subduction of one oceanic plate
beneath another.
Volcanic neck An isolated, steepsided, erosional remnant consisting
of lava that once occupied the vent
of a volcano.
Volcano A mountain formed from
lava and/or pyroclastics.
Wash A desert stream course that
is typically dry except for brief
periods immediately following
rainfall.
Water gap A pass through a ridge
or mountain in which a stream
flows.
Water table The upper level of
the saturated zone of groundwater.
Wave-cut cliff A seaward-facing
cliff along a steep shoreline formed
by wave erosion at its base and by
mass wasting.
Wave-cut platform A bench or
shelf along a shore at sea level, cut
by wave erosion.
Wave height The vertical distance
between the trough and crest of a
wave.
Wave length The horizontal
distance separating successive crests
or troughs.
Wave period The time interval
between the passage of successive
crests at a stationary point.
Weathering The disintegration
and decomposition of rock at or
near the surface of the Earth.
Welded tuff A pyroclastic deposit
composed of particles fused
543
GLOSSARY
increases its brightness many
thousands of times.
Superposition, law of In any
undeformed sequence of
sedimentary rocks, each bed is older
than the one above and younger
than the one below.
Surf A collective term for
breakers; also the wave activity in
the area between the shoreline and
the outer limit of breakers.
Surface soil The upper portion of
a soil profile consisting of the O and
A horizons.
Surface waves Seismic waves
that travel along the outer layer of
Earth.
Surge A period of rapid glacial
advance; surges are typically
sporadic and short-lived.
Suspended load The fine
sediment carried within the body of
flowing water or air.
Swells Wind-generated waves
that have moved into an area of
weaker winds or calm.
Syncline A linear downfold in
sedimentary strata; the opposite of
anticline.
System A group of interacting or
interdependent parts that form a
complex whole.
Tablemount See Guyot.
Tabular Describing a feature such
as an igneous pluton having two
dimensions that are much longer
than the third.
Talus An accumulation of rock
debris at the base of a cliff.
Tarn A small lake in a cirque.
Tectonic plate See Lithospheric
plate.
Tectonics The study of the
large-scale processes that collectively
deform Earth’ s crust.
Temporary (local) base level
The level of a lake, resistant rock
layer, or any other base level that
stands above sea level.
Tenacity Describes a mineral’ s
toughness or its resistance to
breaking or deforming.
Terminal moraine The end
moraine marking the farthest
advance of a glacier.
Terrace A flat, benchlike structure
produced by a stream that was left
elevated as the stream cut
downward.
Terrane A crustal block bounded
by faults whose geologic history is
distinct from the histories of
adjoining crustal blocks.
Terrigenous sediment Seafloor
sediment derived from terrestrial
weathering and erosion.
Texture The size, shape, and
distribution of the particles that
collectively constitute a rock.
Theory A well-tested and widely
accepted view that explains certain
observable facts.
Thermal metamorphism See
Contact metamorphism.
Thrust fault A low-angle reverse
fault.
Tide Periodic change in the
elevation of the ocean’ s surface.
Till Unsorted sediment deposited
directly by a glacier.
Tillite A rock formed when glacial
till is lithified.
Tombolo A ridge of sand that
connects an island to the mainland
or to another island.
Topset bed An essentially
horizontal sedimentary layer
deposited on top of a delta during
floodstage.
Transform fault A major
strike-slip fault that cuts through the
lithosphere and accommodates
motion between two plates.
Transform fault boundary A
boundary in which two plates slide
past one another without creating or
destroying lithosphere.
Transpiration The release of
water vapor to the atmosphere by
plants.
Transported soil Soils that form
on unconsolidated deposits.
Transverse dunes A series of long
ridges oriented at right angles to the
prevailing wind; these dunes form
where vegetation is sparse and sand
is very plentiful.
Travertine A form of limestone
that is deposited by hot springs or as
a cave deposit.
Trellis drainage A system of
streams in which nearly parallel
tributaries occupy valleys cut in
folded strata.
Trench An elongate depression in
the seafloor produced by bending of
oceanic crust during subduction.
Tsunami The Japanese word for a
seismic sea wave.
Turbidite Turbidity current
deposit characterized by graded
bedding.
Turbidity current A downslope
movement of dense, sediment-laden
water created when sand and mud
on the continental shelf and slope
are dislodged and thrown into
suspension.
Turbulent flow The movement of
water in an erratic fashion often
characterized by swirling,
whirlpool-like eddies. Most
streamflow is of this type.
Ultimate base level Sea level; the
lowest level to which stream erosion
could lower the land.
Ultramafic Compositional
category for igneous rocks made up
almost entirely of ferromagnesian
minerals (mostly olivine and
pyroxene).
Unconformity A surface that
represents a break in the rock
record; caused by erosion or
nondeposition.
Uniformitarianism The concept
that the processes that have shaped
Earth in the geologic past are
essentially the same as those
operating today.
Unsaturated zone The area
above the water table where
openings in soil, sediment, and rock
are not saturated with water but
filled mostly with air.
Valence electron The electrons
involved in the bonding process; the
electrons occupying the highest
principal energy level of an atom.
Valley glacier A glacier confined
to a mountain valley, which in most
instances had previously been a
stream valley.
Valley train A relatively narrow
body of stratified drift deposited on
a valley floor by meltwater streams
that issue from the terminus of a
valley glacier.
Vein deposit A mineral filling a
fracture or fault in a host rock. Such
deposits have a sheetlike, or tabular,
form.
Ventifact A cobble or pebble
polished and shaped by the
sandblasting effect of wind.
Vesicles Spherical or elongated
openings on the outer portion of a
lava flow that were created by
escaping gases.
Vesicular texture A term applied
to aphanitic igneous rocks that
contain many small cavities, called
vesicles.
Viscosity A measure of a fluid’ s
resistance to flow.
Volatiles Gaseous components
of magma dissolved in the
melt. Volatiles will readily
vaporize (form a gas) at surface
pressures.
Volcanic Pertaining to the
activities, structures, or rock types of
a volcano.
Volcanic bomb A streamlined
pyroclastic fragment ejected from a
volcano while the fragment is still
molten.
Volcanic island arc A chain of
volcanic islands generally located a
few hundred kilometers from a
trench where there is active
subduction of one oceanic plate
beneath another.
Volcanic neck An isolated, steepsided, erosional remnant consisting
of lava that once occupied the vent
of a volcano.
Volcano A mountain formed from
lava and/or pyroclastics.
Wash A desert stream course that
is typically dry except for brief
periods immediately following
rainfall.
Water gap A pass through a ridge
or mountain in which a stream
flows.
Water table The upper level of
the saturated zone of groundwater.
Wave-cut cliff A seaward-facing
cliff along a steep shoreline formed
by wave erosion at its base and by
mass wasting.
Wave-cut platform A bench or
shelf along a shore at sea level, cut
by wave erosion.
Wave height The vertical distance
between the trough and crest of a
wave.
Wave length The horizontal
distance separating successive crests
or troughs.
Wave period The time interval
between the passage of successive
crests at a stationary point.
Weathering The disintegration
and decomposition of rock at or
near the surface of the Earth.
Welded tuff A pyroclastic deposit
composed of particles fused
543
GLOSSARY