Settling velocity The speed at
which a particle falls through a still
fluid. The size, shape, and specific
gravity of particles influence settling
velocity.
Shadow zone The zone between
105 and 140 degrees distance from
an earthquake epicenter that direct
waves do not penetrate because of
refraction by Earth’ s core.
Shallow-focus earthquake An
earthquake focus at a depth of less
than 60 kilometers.
Shear Stress that causes two
adjacent parts of a body to slide past
one another.
Sheet flow Runoff moving in
unconfined thin sheets.
Sheeting A mechanical
weathering process characterized by
the splitting off of slablike sheets of
rock.
Shelf break The point at which a
rapid steepening of the gradient
occurs, marking the outer edge of
the continental shelf and the
beginning of the continental slope.
Shield A large, relatively flat
expanse of ancient metamorphic
rock within the stable continental
interior.
Shield volcano A broad, gently
sloping volcano built from fluid
basaltic lavas.
Shock metamorphism
Metamorphic alteration of rock by
high speed impact of an
extraterrestrial body such as a
meteorite.
Shore Seaward of the coast, this
zone extends from the highest level
of wave action during storms to the
lowest tide level.
Shoreline The line that marks the
contact between land and sea; it
migrates up and down as the tide
rises and falls.
Silicate Any one of numerous
minerals that have the siliconoxygen tetrahedron as their basic
structure.
Silicon-oxygen tetrahedron
A structure composed of four
oxygen atoms surrounding a
silicon atom that constitutes the
basic building block of silicate
minerals.
Sill A tabular igneous body that
was intruded parallel to the layering
of preexisting rock.
Sinkhole A depression produced
in a region where soluble rock has
been removed by groundwater.
Slab pull A mechanism that
contributes to plate motion in which
cool, dense oceanic crust sinks into
the mantle and “pulls” the trailing
lithosphere along.
Slaty cleavage The type of
foliation characteristic of slates in
which there is a parallel
arrangement of fine-grained
metamorphic minerals.
Slide A movement common to
mass-wasting processes in which the
material moving downslope remains
fairly coherent and moves along a
well-defined surface.
Slip face The steep, leeward
surface of a sand dune that
maintains a slope of about 34
degrees.
Slump The downward slipping of
a mass of rock or unconsolidated
material moving as a unit along a
curved surface.
Snowfield An area where snow
persists year-round.
Snowline Lower limit of
perennial snow.
Soil A combination of mineral
and organic matter, water, and air;
that portion of the regolith that
supports plant growth.
Soil horizon A layer of soil that
has identifiable characteristics
produced by chemical weathering
and other soil-forming processes.
Soil profile A vertical section
through a soil showing its
succession of horizons and the
underlying parent material.
Soil Taxonomy A soil
classification system consisting of
six hierarchical categories based on
observable soil characteristics. The
system recognizes 12 soil orders.
Solar nebula The cloud of
interstellar gas and/or dust from
which the bodies of our solar system
formed.
Solifluction Slow, downslope
flow of water-saturated materials
common to permafrost areas.
Solum The O, A, and B horizons
in a soil profile; living roots and
other plant and animal life are
largely confined to this zone.
Solution The change of matter
from the solid or gaseous state into
the liquid state by its combination
with a liquid.
Sorting The degree of similarity in
particle size in sediment or
sedimentary rock.
Specific gravity The ratio of a
substance’ s weight to the weight of
an equal volume of water.
Speleothem A collective term for
the dripstone features found in
caverns.
Spheroidal weathering Any
weathering process that tends to
produce a spherical shape from an
initially blocky shape.
Spit An elongated ridge of sand
that projects from the land into the
mouth of an adjacent bay.
Spreading center See Divergent
plate boundary.
Spring A flow of groundwater
that emerges naturally at the ground
surface.
Spring tide The highest tidal
range; occurs near the times of the
new and full moons.
Stable platform That part of the
craton that is mantled by relatively
undeformed sedimentary rocks and
underlain by a basement complex of
igneous and metamorphic rocks.
Stalactite The iciclelike structure
that hangs from the ceiling of a
cavern.
Stalagmite The columnlike form
that grows upward from the floor of
a cavern.
Star dune Isolated hill of sand
that exhibits a complex form and
develops where wind conditions
are variable.
Steppe One of the two types of
dry climate. A marginal and more
humid variant of the desert that
separates the desert from bordering
humid climates.
Stock A pluton similar to but
smaller than a batholith.
Strata Parallel layers of
sedimentary rock.
Stratified drift Sediments
deposited by glacial meltwater.
Stratovolcano See Composite
cone.
Streak The color of a mineral in
powdered form.
Stream A general term to denote
the flow of water within any natural
channel. Thus, a small creek and a
large river are both streams.
Stream valley The channel, valley
floor, and the sloping valley walls of
a stream.
Stress The force per unit area
acting on any surface within a solid.
Striations The multitude of fine
parallel lines found on some
cleavage faces of plagioclase
feldspars but not present on
orthoclase feldspar.
Striations (glacial) Scratches or
grooves in a bedrock surface caused
by the grinding action of a glacier
and its load of sediment.
Strike The compass direction of
the line of intersection created by a
dipping bed or fault and a
horizontal surface. Strike is always
perpendicular to the direction of
dip.
Strike-slip fault A fault along
which the movement is horizontal.
Stromatolite Structures that are
deposited by algae and that consist
of layered mounds or columns of
calcium carbonate.
Subduction The process of
thrusting oceanic lithosphere into
the mantle along a convergent
zone.
Subduction zone A long, narrow
zone where one lithospheric plate
descends beneath another.
Subduction zone metamorphism
High-pressure, low-temperature
metamorphism that occurs where
sediments are carried to great
depths by a subducting plate.
Submarine canyon A seaward
extension of a valley that was cut on
the continental shelf, slope, and rise
by turbidity currents.
Submergent coast A coast whose
form is largely the result of the
partial drowning of a former land
surface due either to a rise of sea
level or subsidence of the crust,
or both.
Subsoil A term applied to the B
horizon of a soil profile.
Supercontinent A huge landmass
that consists of all, or nearly all, of
the existing continents combined
into one.
Supercontinent cycle The idea
that the rifting and dispersal of one
supercontinent is followed by a long
period during which the fragments
gradually reassemble into a new
supercontinent.
GLOSSARY
542
which a particle falls through a still
fluid. The size, shape, and specific
gravity of particles influence settling
velocity.
Shadow zone The zone between
105 and 140 degrees distance from
an earthquake epicenter that direct
waves do not penetrate because of
refraction by Earth’ s core.
Shallow-focus earthquake An
earthquake focus at a depth of less
than 60 kilometers.
Shear Stress that causes two
adjacent parts of a body to slide past
one another.
Sheet flow Runoff moving in
unconfined thin sheets.
Sheeting A mechanical
weathering process characterized by
the splitting off of slablike sheets of
rock.
Shelf break The point at which a
rapid steepening of the gradient
occurs, marking the outer edge of
the continental shelf and the
beginning of the continental slope.
Shield A large, relatively flat
expanse of ancient metamorphic
rock within the stable continental
interior.
Shield volcano A broad, gently
sloping volcano built from fluid
basaltic lavas.
Shock metamorphism
Metamorphic alteration of rock by
high speed impact of an
extraterrestrial body such as a
meteorite.
Shore Seaward of the coast, this
zone extends from the highest level
of wave action during storms to the
lowest tide level.
Shoreline The line that marks the
contact between land and sea; it
migrates up and down as the tide
rises and falls.
Silicate Any one of numerous
minerals that have the siliconoxygen tetrahedron as their basic
structure.
Silicon-oxygen tetrahedron
A structure composed of four
oxygen atoms surrounding a
silicon atom that constitutes the
basic building block of silicate
minerals.
Sill A tabular igneous body that
was intruded parallel to the layering
of preexisting rock.
Sinkhole A depression produced
in a region where soluble rock has
been removed by groundwater.
Slab pull A mechanism that
contributes to plate motion in which
cool, dense oceanic crust sinks into
the mantle and “pulls” the trailing
lithosphere along.
Slaty cleavage The type of
foliation characteristic of slates in
which there is a parallel
arrangement of fine-grained
metamorphic minerals.
Slide A movement common to
mass-wasting processes in which the
material moving downslope remains
fairly coherent and moves along a
well-defined surface.
Slip face The steep, leeward
surface of a sand dune that
maintains a slope of about 34
degrees.
Slump The downward slipping of
a mass of rock or unconsolidated
material moving as a unit along a
curved surface.
Snowfield An area where snow
persists year-round.
Snowline Lower limit of
perennial snow.
Soil A combination of mineral
and organic matter, water, and air;
that portion of the regolith that
supports plant growth.
Soil horizon A layer of soil that
has identifiable characteristics
produced by chemical weathering
and other soil-forming processes.
Soil profile A vertical section
through a soil showing its
succession of horizons and the
underlying parent material.
Soil Taxonomy A soil
classification system consisting of
six hierarchical categories based on
observable soil characteristics. The
system recognizes 12 soil orders.
Solar nebula The cloud of
interstellar gas and/or dust from
which the bodies of our solar system
formed.
Solifluction Slow, downslope
flow of water-saturated materials
common to permafrost areas.
Solum The O, A, and B horizons
in a soil profile; living roots and
other plant and animal life are
largely confined to this zone.
Solution The change of matter
from the solid or gaseous state into
the liquid state by its combination
with a liquid.
Sorting The degree of similarity in
particle size in sediment or
sedimentary rock.
Specific gravity The ratio of a
substance’ s weight to the weight of
an equal volume of water.
Speleothem A collective term for
the dripstone features found in
caverns.
Spheroidal weathering Any
weathering process that tends to
produce a spherical shape from an
initially blocky shape.
Spit An elongated ridge of sand
that projects from the land into the
mouth of an adjacent bay.
Spreading center See Divergent
plate boundary.
Spring A flow of groundwater
that emerges naturally at the ground
surface.
Spring tide The highest tidal
range; occurs near the times of the
new and full moons.
Stable platform That part of the
craton that is mantled by relatively
undeformed sedimentary rocks and
underlain by a basement complex of
igneous and metamorphic rocks.
Stalactite The iciclelike structure
that hangs from the ceiling of a
cavern.
Stalagmite The columnlike form
that grows upward from the floor of
a cavern.
Star dune Isolated hill of sand
that exhibits a complex form and
develops where wind conditions
are variable.
Steppe One of the two types of
dry climate. A marginal and more
humid variant of the desert that
separates the desert from bordering
humid climates.
Stock A pluton similar to but
smaller than a batholith.
Strata Parallel layers of
sedimentary rock.
Stratified drift Sediments
deposited by glacial meltwater.
Stratovolcano See Composite
cone.
Streak The color of a mineral in
powdered form.
Stream A general term to denote
the flow of water within any natural
channel. Thus, a small creek and a
large river are both streams.
Stream valley The channel, valley
floor, and the sloping valley walls of
a stream.
Stress The force per unit area
acting on any surface within a solid.
Striations The multitude of fine
parallel lines found on some
cleavage faces of plagioclase
feldspars but not present on
orthoclase feldspar.
Striations (glacial) Scratches or
grooves in a bedrock surface caused
by the grinding action of a glacier
and its load of sediment.
Strike The compass direction of
the line of intersection created by a
dipping bed or fault and a
horizontal surface. Strike is always
perpendicular to the direction of
dip.
Strike-slip fault A fault along
which the movement is horizontal.
Stromatolite Structures that are
deposited by algae and that consist
of layered mounds or columns of
calcium carbonate.
Subduction The process of
thrusting oceanic lithosphere into
the mantle along a convergent
zone.
Subduction zone A long, narrow
zone where one lithospheric plate
descends beneath another.
Subduction zone metamorphism
High-pressure, low-temperature
metamorphism that occurs where
sediments are carried to great
depths by a subducting plate.
Submarine canyon A seaward
extension of a valley that was cut on
the continental shelf, slope, and rise
by turbidity currents.
Submergent coast A coast whose
form is largely the result of the
partial drowning of a former land
surface due either to a rise of sea
level or subsidence of the crust,
or both.
Subsoil A term applied to the B
horizon of a soil profile.
Supercontinent A huge landmass
that consists of all, or nearly all, of
the existing continents combined
into one.
Supercontinent cycle The idea
that the rifting and dispersal of one
supercontinent is followed by a long
period during which the fragments
gradually reassemble into a new
supercontinent.
GLOSSARY
542