Book Glossary Flashcards - Essentials of Geo P1
A type of lava flow that has a
jagged, blocky surface.
aa
A general term for the
loss of ice and snow from a glacier.
Ablation
The grinding and
scraping of a rock surface by the
friction and impact of rock particles
carried by water, wind, or ice.
Abrasion
Very level area of
the deep-ocean floor, usually lying
at the foot of the continental rise
Abyssal plain
A large
wedge-shaped mass of sediment
that accumulates in subduction
zones. Here sediment is scraped
from the subducting oceanic plate
and accreted to the overriding
crustal block.
Accretionary wedge
Usually narrow and consisting of
highly deformed sediments, they
occur where oceanic lithosphere is
being subducted beneath the
margin of a continent.
Active continental margin
The zone above the
permafrost that thaws in summer
and refreezes in winter.
Active layer
Tiny solid and liquid
particles suspended in the
atmosphere.
Aerosols
A smaller earthquake
that follows the main earthquake.
Aftershock
A stream
channel in which the bed and
banks are composed largely of
unconsolidated sediment (alluvium)
that was previously deposited in the
valley
Alluvial channel
A fan-shaped deposit
of sediment formed when a stream’s
slope is abruptly reduced.
Alluvial fan
Unconsolidated
sediment deposited by a stream
Alluvium
A type of convergent boundary in
which a slab of oceanic crust is
subducting beneath a continental
margin.
Andean-type plate margin
Igneous rocks having a
mineral makeup between that of
granite and basalt, after the common
volcanic rock andesite.
Andesitic
The steepest
angle at which loose material
remains stationary without sliding
downslope.
Angle of repose
An unconformity in which the older
strata dip at an angle different from
that of the younger beds.
Angular unconformity
A hard, metamorphic
form of coal that burns clean and
hot
Anthracite
A fold in sedimentary
strata that resembles an arch.
Anticline
A texture of
igneous rocks in which the crystals
are too small for individual minerals
to be distinguished with the
unaided eye.
Aphanitic texture
Rock or sediment
through which groundwater moves
easily.
Aquifer
An impermeable bed
that hinders or prevents
groundwater movement.
Aquitard
The first eon of
Precambrian time; the eon
preceding the Proterozoic. It
extends between 4.5 and 2.5 billion
years ago.
Archean eon
A narrow, knifelike ridge
separating two adjacent glaciated
valleys
Arête
A feldspar-rich sandstone.
Arkose
A well in which the
water rises above the level where it
was initially encountered
Artesian well
A subdivision of
the mantle situated below the
lithosphere. This zone of weak
material exists below a depth of
about 100 kilometers and in some
regions extends as deep as 700
kilometers. The rock within this
zone is easily deformed.
Asthenosphere
The gaseous portion
of a planet; the planet’s envelope of
air. One of the traditional
subdivisions of Earth’s physical
environment
Atmosphere
A continuous or broken ring
of coral reef surrounding a central
lagoon.
Atoll
The smallest particle that
exists as an element.
Atom
A mass unit
equal to exactly one-twelfth the
mass of a carbon-12 atom
Atomic mass unit
The number of
protons in the nucleus of an atom
Atomic number
The average of the
atomic masses of isotopes of a given
element.
Atomic weight
A zone or halo of contact
metamorphism found in the host
rock surrounding an igneous
intrusion
Aureole
A poorly drained
area on a floodplain, resulting when
natural levees are present.
Back swamp
The inner portion of
the shore, lying landward of the
high-tide shoreline. It is usually dry,
being affected by waves only during
storms.
Backshore
An apron of sediment
along a mountain front created by
the coalescence of alluvial fans
Bajada
Finely
layered iron- and silica-rich (chert)
layers deposited mainly during the
Precambrian
Banded iron formations
Common term for sand and
gravel deposits in a stream channel.
-Bar
-Channel
-Alluvium
Bar
A solitary sand
dune shaped like a crescent with its
tips pointed downwind
Barchan dune
Dunes forming scalloped rows of sand
oriented at right angles to the wind.
This form is intermediate between
isolated barchans and extensive
waves of transverse dunes.
Barchanoid dunes
A low, elongated
ridge of sand that parallels the coast.
Barrier island
A mechanism of glacial
movement in which the ice mass
slides over the surface below
Basal slip
An aphanitic igneous rock
of mafic composition.
Basalt
Term used to describe
igneous rocks that contain abundant
dark (ferromagnesian) minerals and
about 50 percent silica.
Basaltic
The level below which
a stream cannot erode
Base level
A circular downfolded
structure.
Basin
A large mass of igneous
rock that formed when magma was
emplaced at depth, crystallized, and
was subsequently exposed by
erosion.
Batholith
A sandbar that
completely crosses a bay, sealing it
off from the main body of water
Baymouth bar
An accumulation of
sediment found along the landward
margin of the ocean or a lake
Beach
The transport of
sediment in a zigzag pattern along a
beach. It is caused by the uprush of water from obliquely breaking
waves.
Beach drift
The wet, sloping
surface that extends from the berm
to the shoreline
Beach face
Large quantities of sand are added to the
beach system to offset losses caused
by wave erosion. By building
beaches seaward, beach quality and
storm protection are both improved.
Beach nourishment
Sediment rolled along
the bottom of a stream by moving
water, or particles rubbed along the
ground surface by wind.
Bed load
A nearly flat
surface separating two beds of
sedimentary rock. Each bedding
plane marks the end of one deposit
and the beginning of another having
different characteristics.
Bedding plane
A general term for the
rock that underlies soil or other
unconsolidated surface materials.
Bedrock
A zone in
which water is held as a film on the
surface of soil particles and may be
used by plants or withdrawn by
evaporation. The uppermost
subdivision of the zone of aeration
Belt of soil moisture
The dry, gently sloping zone
on the backshore of a beach at the
foot of the coastal cliffs or dunes
Berm
Describing a type of
chemical sediment that forms when
material dissolved in water is
precipitated by water-dwelling
organisms. Shells are common
examples.
Biochemical
Seafloor
sediments consisting of material of
marine-organic origin.
Biogenous sediment
The most
common form of coal, often called
soft, black coal.
Bituminous coal
Lava having a surface
of angular blocks associated with
material having andesitic and
rhyolitic compositions.
Block lava
A depression excavated by wind in
easily eroded materials.
Blowout (deflation hollow)
A seismic wave that
travels through Earth’s interior
Body wave
A layer of fine sediment deposited beyond the
advancing edge of a delta and then
buried by continuous delta growth.
Bottomset bed
A concept proposed by N. L. Bowen
that illustrates the relationship
between magma and the minerals
crystallizing from it during the
formation of igneous rock.
Bowen’s reaction series
A stream consisting of numerous intertwining
channels.
Braided stream
A structure protecting a nearshore area from
breaking waves.
Breakwater
A sedimentary rock
composed of angular fragments that
were lithified.
Breccia
Deformation
that involves the fracturing of rock.
Associated with rocks near the
surface.
Brittle deformation
Lowgrade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata.
- Zeolite Facies
- Diagenesis
- Burial Metamorphism
Burial metamorphism
A large depression
typically caused by collapse of the
summit area of a volcano following
a violent eruption.
Caldera
A hard layer, rich in
calcium carbonate, that forms
beneath the B horizon in soils of arid
regions.
Caliche
Wastage of a glacier that
occurs when large pieces of ice
break off into water.
Calving
A necessary part of
an oil trap, the _____ is
impermeable and hence keeps
upwardly mobile oil and gas from
escaping at the surface.
Cap rock
The total amount of
sediment a stream is able to
transport
Capacity
A relatively
narrow zone at the base of the zone
of aeration. Here water rises from
the water table in tiny threadlike
openings between grains of soil or
sediment
Capillary fringe
The concept that
Earth was shaped by catastrophic
events of a short-term nature.
Catastrophism
A naturally formed
underground chamber or series of
chambers most commonly
produced by solution activity in
limestone.
Cavern
One way in which
sedimentary rocks are lithified. As
material precipitates from water that
percolates through the sediment,
open spaces are filled and particles
are joined into a solid mass.
Cementation
A time span on the
geologic time scale beginning about
65.5 million years ago following the
Mesozoic era.
Cenozoic era
A strong attractive force that exists between
atoms in a substance. It involves the
transfer or sharing of electrons that
allows each atom to attain a full
valence shell.
Chemical bond
Sedimentary rock consisting of
material that was precipitated from
water by either inorganic or organic
means.
Chemical sedimentary rock
The processes by which the internal
structure of a mineral is altered by
the removal and/or addition of
elements.
Chemical weathering
A rather small
volcano built primarily of pyroclastics
ejected from a single vent.
Cinder cone
An amphitheater-shaped
basin at the head of a glaciated
valley produced by frost wedging
and plucking.
Cirque
A sedimentary rock
texture consisting of broken
fragments of preexisting rock.
Clastic
The tendency of a
mineral to break along planes of
weak bonding.
Cleavage
Because the atmosphere is a
complex interactive physical system,
several different outcomes may
result when one of the system’s
elements is altered. These various
possibilities are called _________
Climate feedback mechanism
The exchanges of
energy and moisture occurring
among the atmosphere,
hydrosphere, geosphere, biosphere,
and cryosphere.
Climate system
A strip of land that
extends inland from the coastline
as far as ocean-related features can
be found.
Coast
The coast’s seaward
edge; the landward limit of the effect
of the highest storm waves on the
shore.
Coastline
A pass between mountain
valleys where the headwalls of two
cirques intersect.
Col
A phenomenon of light by
which otherwise identical objects
may be differentiated.
Color
A feature found in caves
that is formed when a stalactite and
stalagmite join.
-Column
-spleothoems
-travertine deposits
Column
A pattern of
cracks that forms during cooling of
molten rock to generate columns
Columnar joints
A type of
lithification in which the weight of
overlying material compresses more
deeply buried sediment. It is most
important in fine-grained
sedimentary rocks such as shale
Compaction
A measure of the
largest particle a stream can transport;
a factor dependent on velocity.
Competence
A volcano
composed of both lava flows and
pyroclastic material.
Composite Cone
Mountains in which great horizontal
forces have shortened and
thickened the crust. Most major
mountain belts are of this type.
Compressional Mountains
A term used to
describe intrusive igneous masses
that form parallel to the bedding of
the surrounding rock.
Concordant
A pipelike opening
through which magma moves
toward Earth’s surface. It terminates
at a surface opening called a vent.
Conduit
An aquifer that
has impermeable layers (aquitards)
both above and below.
Confined
A coneshaped
depression immediately
surrounding a well.
Cone of depression
Rock layers
that were deposited without
interruption.
Conformable layers
A sedimentary
rock consisting of rounded,
gravel-size particles.
Conglomerate
Changes in rock caused by the heat
of a nearby magma body.
Contact Metamorphism
A hypothesis,credited largely to Alfred Wegener,
that suggested all present continents
once existed as a single
supercontinent.
Continental Drift
A linear zone
along which continental lithosphere
stretches and pulls apart. Its creation
may mark the beginning of a new
ocean basin.
Continental rift
The gently
sloping surface at the base of the
continental slope.
Continental Rise
The gently
sloping submerged portion of the
continental margin, extending from
the shoreline to the continental
slope
Continental shelf
The steep
gradient that leads to the deepocean
floor and marks the seaward
edge of the continental shelf.
Continental slope
Mountains formed in part by
igneous activity associated with the
subduction of oceanic lithosphere
beneath a continent. Examples
include the Andes and the
Cascades.
Continental volcanic arc
A boundary in which two plates move
together, resulting in oceanic
lithosphere being thrust beneath an
overriding plate, eventually to be
reabsorbed into the mantle.
Convergent plate boundary
Located beneath the mantle,
it is Earth’s innermost layer. The
core is divided into an outer core
and an inner core.
Core
Establishing the
equivalence of rocks of similar age
in different areas.
Correlation
A chemical bond produced by the sharing of
electrons.
Covalent bond
The depression at the
summit of a volcano, or that which
is produced by a meteorite impact
Crater
That part of the continental
crust that has attained stability; that
is, it has not been affected by
significant tectonic activity during the
Phanerozoic eon. It consists of the
shield and stable platform.
Craton
The slow downhill
movement of soil and regolith.
Creep
A deep crack in the
brittle surface of a glacier.
Crevasse
Structure in which
relatively thin layers are inclined at
an angle to the main bedding.
Formed by currents of wind or water.
Cross-bedding
A principle of
relative dating. A rock or fault is
younger than any rock (or fault)
through which it cuts.
Cross-cutting
The very thin, outermost
layer of Earth
Crust
An orderly arrangement
of atoms
Crystal
The formation
and growth of a crystalline solid
from a liquid or gas
Crystallization
The temperature
above which a material loses its
magnetization.
Curie point
The area of active
erosion on the outside of a meander.
Cut bank
A short channel segment
created when a river erodes through
the narrow neck of land between
meanders.
Cutoff
Silicate minerals
containing ions of iron and/or
magnesium in their structure. They
are dark in color and have a higher
specific gravity than
nonferromagnesian silicates.
Dark silicate
An isotope resulting from radioactive decay.
Daughter product
A relatively rapid
type of mass wasting that involves a
flow of soil and regolith containing a
large amount of water; also called
mudflows.
Debris flow
Melting that occurs as rock ascends due to a
drop in confining pressure
Decompression melting
An earthquake focus at a depth of more
than 300 kilometers.
Deep-focus earthquake
The portion of
seafloor that lies between the
continental margin and the oceanic
ridge system. This region comprises
almost 30 percent of Earth’s surface.
Deep-ocean basin
The lifting and removal
of loose material by wind.
Deflation
General term for
the processes of folding, faulting,
shearing, compression, or extension
of rocks as the result of various
natural forces
Deformation
An accumulation of
sediment formed where a stream
enters a lake or ocean
Delta
A stream system that resembles the
pattern of a branching tree.
Dendritic drainage pattern
The weight per unit
volume of a particular material.
Density
One of the two types of
dry climate; the drier of the dry
climates.
Desert
A layer of coarse pebbles and gravel created when wind removes the finer
material.
Desert pavement
A low-angle
fault that represents a major
boundary between unfaulted rocks
below that exhibit ductile
deformation and rocks above that
exhibit brittle deformation via
faulting.
Detachment fault
Rocks that form from the accumulation of
materials that originate and are
transported as solid particles derived
from both mechanical and chemical
weathering.
Detrital sedimentary rocks
A collective term for
all the chemical, physical, and
biological changes that take place
after sediments are deposited and
during and after lithification.
Diagenesis
A tabular-shaped intrusive
igneous feature that cuts through
the surrounding rock.
Dike
The angle at which a rock
layer is inclined from the horizontal.
The direction of dip is at a right
angle to the strike.
Dip
A fault in which
the movement is parallel to the dip
of the fault.
Dip-slip fault
The quantity of water in a stream that passes a given point
in a given period of time.
Discharge
A type of unconformity in which the beds
above and below are parallel
Disconformity
A sudden change
with depth in one or more of the
physical properties of the material
making up Earth’s interior
Discontinuity
The boundary between two dissimilar
materials in Earth’s interior as
determined by the behavior of
seismic waves.
A term used to
describe plutons that cut across
existing rock structures, such as
bedding planes.
Discordant
Any economic mineral deposit in which
the desired mineral occurs as
scattered particles in the rock but in
sufficient quantity to make the
deposit an ore.
Disseminated deposit
The portion of a
stream’s load carried in solution.
Dissolved load
A section of a stream
that leaves the main flow.
Distributary
A tide characterized
by a single high and low water
height each tidal day.
Diurnal tide
A boundary in which two plates move
apart, resulting in upwelling of
material from the mantle to create
new seafloor.
Divergent plate boundary
An imaginary line that
separates the drainage of two
streams; often found along a ridge.
Divide
A roughly circular,
upfolded structure.
Dome
The land area
that contributes water to a stream.
Drainage basin
The difference in
height between the bottom of a cone
of depression and the original height
of the water table.
Drawdown
A streamlined
asymmetrical hill composed of
glacial till. The steep side of the hill
faces the direction from which the
ice advanced.
Drumlin
A climate in which
the yearly precipitation is less than
the potential loss of water by
evaporation.
Dry Climate
A type of
solid-state flow that produces a
change in the size and shape of a
rock body without fracturing.
Occurs at depths where temperatures and confining
pressures are high.
Ductile deformation
A hill or ridge of
wind-deposited sand.
Dune
The downslope
movement of water-saturated,
clay-rich sediment, most
characteristic of humid regions
Earthflow
The vibration of
Earth produced by the rapid release
of energy.
Earthquake
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.
Echo sounder
Nonpermanent deformation in
which rock returns to its original
shape when the stress is released.
Elastic deformation
The sudden
release of stored strain in rocks that
results in movement along a fault
Elastic rebound
The washing out of
fine soil components from the A
horizon by downward-percolating
water.
Eluviation
A coast where
land formerly below the sea level
has been exposed by either crustal
uplift or a drop in sea level or both.
Emergent coast
A ridge of till
marking a former position of the
front of the glacier.
End moraine
Spherically shaped
negatively charged zones that
surround the nucleus of an atom
Energy levels
The largest time unit on the
geologic time scale, next in order of
magnitude above era.
Eon
The location on Earth’s
surface that lies directly above the
focus of an earthquake.
Epicenter
A unit of the geological
time scale that is a subdivision of a
period.
Epoch
A major division on the
geologic time scale; are divided
into shorter units called periods.
Eras
The incorporation and
transportation of material by a
mobile agent, such as water, wind,
or ice.
Erosion
Buoyant plumes of hot ash-laden gases that
can extend thousands of meters into
the atmosphere
Eruption column
Sinuous ridge composed
largely of sand gravel deposited
by a stream flowing in a tunnel
beneath a glacier near its
terminus.
Esker
A partially enclosed
coastal water body that is connected
to the ocean. Salinity here is
measurably reduced by the
freshwater flow of rivers.
Estuary
Organisms whose
genetic material is enclosed in a
nucleus. Plants, animals, and fungi
are eukaryotes.
Eukaryotes
A sedimentary rock
formed of material deposited from
solution by evaporation of water
Evaporite
The combined effect of evaporation and
transpiration.
Evapotranspiration
Large, dome-shaped structure, usually
composed of granite, formed by
sheeting.
Exfoliation dome
A permanent stream that traverses a desert and
has its source in well-watered areas
outside the desert.
Exotic stream
Process such as weathering, mass wasting, or
erosion that is powered by the Sun
and transforms solid rock into
sediment.
External process
Igneous activity that
occurs at Earth’s surface.
Extrusive
A zone of scattered clouds
and calm averaging about 20
kilometers in diameter at the center
of a hurricane.
Eye
A doughnut-shaped area
of intense cumulonimbus
(thunderstorm) development and
very strong winds that surrounds
the eye of a hurricane.
Eye wall
A type of movement
common to mass-wasting processes
that refers to the free falling of
detached individual pieces of any
size.
Fall
A break in a rock mass
along which movement has
occurred.
Fault
Slow, gradual
displacement along a fault that
occurs relatively smoothly and with
little noticeable seismic activity.
Fault creep
A cliff created by
movement along a fault. It
represents the exposed surface of
the fault prior to modification by
weathering and erosion.
Fault scarp
A mountain formed by the
displacement of rock along a fault.
Fault-block mountain
A term derived from
feldspar and silica (quartz). It is a
term used to describe granitic
igneous rocks.
Felsic
The distance that the wind
has traveled across the open water.
Fetch
A steep-sided inlet of the
sea formed when a glacial trough
was partially submerged.
Fjord
A crack in rock along
which there is a distinct separation.
Fissure
An eruption in
which lava is extruded from narrow
fractures or cracks in the crust.
Fissure eruption
The overflow of a stream
channel that occurs when discharge
exceeds the channel’s capacity. The
most common and destructive
geologic hazard.
Flood
Flows of basaltic
lava that issue from numerous
cracks or fissures and commonly
cover extensive areas to thicknesses
of hundreds of meters.
Flood basalts
The flat, low-lying
portion of a stream valley subject to
periodic inundation.
Floodplain
A type of movement
common to mass-wasting processes
in which water-saturated material
moves downslope as a viscous fluid.
Flow
The absorption of
ultraviolet light, which is reemitted
as visible light.
Fluorescence
The zone
within Earth where rock
displacement produces an
earthquake.
Focus (earthquake)
A bent layer or series of
layers that were originally horizontal
and subsequently deformed.
Fold
A texture of
metamorphic rocks that gives the
rock a layered appearance.
Foliated
A term for a linear
arrangement of textural features
often exhibited by metamorphic
rocks.
Folation
An inclined bed
deposited along the front of a delta.
Foreset bed
Small earthquakes
that often precede a major
earthquake.
Foreshocks
That portion of the
shore lying between the normal
high- and low-water marks; the
intertidal zone.
Foreshore
The remains or traces of
organisms preserved from the
geologic past.
Fossil
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 fuel
Fossil organisms succeed one another in a
definite and determinable order, and
any time period can be recognized
by its fossil content.
Fossil succession
The
process that separates magma into
components having varied
compositions and melting points.
Fractional crystallization
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.
Fracture (mineral)
Any break or
rupture in rock along which no
appreciable movement has taken
place.
Fracture (rock)
Linear zone of
irregular topography on the
deep-ocean floor; it follows
transform faults and their inactive
extensions.
Fracture zone
The mechanical
breakup of rock caused by the
expansion of freezing water in
cracks and crevices.
Frost wedging
A vent in a volcanic
area from which fumes or gases
escape.
Fumarole
Streams that gain
water from the inflow of
groundwater through the
streambed.
Gaining stream
The science that
examines Earth, its form and
composition, and the changes
it has undergone and is
undergoing.
Geology
The solid Earth; one
of Earth’s four basic spheres.
Geosphere
Natural steam used for power generation.
Geothermal energy
The gradual increase in temperature
with depth in the crust. The average
is 30 °C per kilometer in the
upper crust.
Geothermal gradient
A fountain of hot water
ejected periodically from the
ground.
Geyser
The balance, or
lack of balance, between
accumulation at the upper end
of a glacier and loss at the
other end.
Glacial budget
An all-embracing
term for sediments of glacial origin,
no matter how, where, or in what
shape they were deposited.
Glacial drift
An ice-transported boulder that was not
derived from the bedrock near its
present site.
Glacial erratic
Scratches and
grooves on bedrock caused by
glacial abrasion.
Glacial striations
A mountain valley
that has been widened, deepened,
and straightened by a glacier.
Glacial trough
A thick mass of ice
originating on land from the
compaction and recrystallization of
snow. The ice shows evidence of
past or present flow.
Glacier
Natural glass
produced when molten lava cools
too rapidly to permit crystallization.
Volcanic glass is a solid composed of
unordered atoms.
Volcanic Glass
A term used to
describe the texture of certain
igneous rocks, such as obsidian, that
contain no crystals.
Glassy texture
The texture
displayed by the metamorphic rock
gneiss in which dark and light
silicate minerals have separated,
giving the rock a banded
appearance.
Gneissic texture
The southern
portion of Pangaea consisting of
South America, Africa, Australia,
India, and Antarctica.
Gondwanaland
A valley formed by the
downward displacement of a
fault-bounded block.
Graben
A sediment layer
characterized by a decrease in
sediment size from bottom to top.
Graded bed
A stream that has
the correct channel characteristics to
maintain the exact velocity required
to transport the material supplied
to it.
Graded stream
The slope of a stream;
generally measured in feet per mile.
Gradient
Igneous rocks composed
mainly of light-colored silicates
(quartz and feldspar) are said to
have this composition.
Granitic
The gradual subsidence of mountains
caused by lateral spreading of weak
material located deep within these
structures.
Gravitational collapse
Carbon dioxide and water vapor in a planet’s
atmosphere absorb and reradiate
infrared wavelengths, effectively
trapping solar energy and raising the
temperature.
Greenhouse effect
A short wall built at a right
angle to the seashore to trap moving
sand.
Groin
An undulating layer of till deposited as the ice front retreats
- Tillites
- Ground Moraine
- Cirque
Ground moraine
The matrix of smaller crystals within an igneous rock that has porphyritic texture.
Groundmass
Water in the zone of saturation
Groundwater
A submerged flat-topped seamount.
-Guyot
-Ridge
-Abbysal plain
Guyot
The common or characteristic shape of a crystal or aggregate of crystals.
-Form
-Habit
-Crystal
Habit
An informal term that refers to the earliest interval(eon) of Earth history—before the oldest known rocks.
Hadeon Eon
A tilted fault block in which the higher side is associated with mountainous topography and the lower side is a basin that fills with sediment
-Triangular Facets
-Orogenic Belts
-Half Graben
Half-Graben
The time required for
one half of the atoms of a radioactive
substance to decay.
Half-life
A tributary valley that enters a glacial trough at a considerable height above the floor of the trough.
-Hanging Valley
-Waterfall
-Drumlin
Hanging valley
A mineral’s resistance to
scratching and abrasion.
Hardness
The vertical distance
between the recharge and discharge
points of a water table. Also, the
source area or beginning of a valley
-Draw down
-Gradient
-Head
Head
The extension
upslope of the head of a valley due
to erosion
Headward erosion
A major division of geology that deals with
the origin of Earth and its
development through time. Usually
involves the study of fossils and
their sequence in rock beds.
Historical geology
A narrow, sharp-crested
ridge formed by the upturned edge
of a steeply dipping bed of resistant
rock.
Hogback
A pyramidlike peak formed
by glacial action in three or more
cirques surrounding a mountain
summit
Horn
An elongated, uplifted
block of crust bounded by faults
Horst
A proposed
concentration of heat in the mantle
capable of introducing magma that
in turn extrudes onto Earth’s
surface. The intraplate volcanism
that produced the Hawaiian Islands
is one example
Hot Spot
A chain of
volcanic structures produced as a
lithospheric plate moves over a
mantle plume.
Hot Spot Track
A spring in which the
water is 6° to 9 °C (10 °C to 15 °F)
warmer than the mean annual air
temperature of its locality.
Hot spring
Organic matter in soil
produced by the decomposition of
plants and animals.
Humus
A factor relating to groundwater flow; it is a
coefficient that takes into account
the permeability of the aquifer and
the viscosity of the fluid.
Hydraulic conductivity
The slope of
the water table. It is determined by
finding the height difference
between the two points on the
water table and dividing by the
horizontal distance between the
two points.
Hydraulic gradient
Seafloor sediments consisting of minerals
that crystallize from seawater. The
principal example is manganese
nodules.
Hydrogenous sediment
The unending
circulation of Earth’s water supply.
The cycle is powered by energy
from the Sun and is characterized by
continuous exchanges of water
among the oceans, the atmosphere,
and the continents.
Hydrologic cycle
A chemicalweathering
process in which
minerals are altered by chemically
reacting with water and acids.
Hydrolysis
The water portion
of our planet; one of the traditional
subdivisions of Earth’s physical
environment.
Hydrosphere
Chemical alterations that occur as
hot, ion-rich water circulates
through fractures in rock.
Hydrothermal metamorphism
The hot, watery solution that escapes from a mass of magma during the latter stages of crystallization.
Hydrothermal solution
A tentative explanation that is then tested to
determine if it is valid.
Hypothesis
A mass of glacial ice
covering a high upland or plateau
and spreading out radially
Ice Cap
A very large, thick mass
of glacial ice flowing outward in all
directions from one or more
accumulation centers
Ice Sheet
An accumulation of stratified drift
deposited in contact with a
supporting mass of ice.
Ice-contact deposit
A rock formed by
the crystallization of molten magma.
Igneous rock
A soil lacking horizons.
Immature Soil
Metamorphism that occurs when
meteorites strike Earth’s surface
Impact metamorphism
Meandering
channel that flows in a steep,
narrow valley. These meanders form
either when an area is uplifted or
when base level drops.
Incised meander
A piece of one rock
unit contained within another;
inclusions are used in relative
dating. The rock mass adjacent to
the one containing the inclusion
must have been there first in order
to provide the fragment.
Inclusion
A fossil that is
associated with a particular span of
geologic time
Index fossil
A mineral that is a
good indicator of the metamorphic
environment in which it formed.
Used to distinguish different zones
of regional metamorphism.
Index mineral
The movement of
surface water into rock or soil
through crack and pore spaces.
Infiltration
The maximum rate at which soil can
absorb water.
Infiltration capacity
The solid, innermost
layer of Earth, about 1216
kilometers (754 miles) in radius.
Inner core
An isolated mountain
remnant characteristic of the late
stage of erosion in a mountainous
region
Inselberg
measure of the degree of earthquake
shaking at a given locale based on
the amount of damage.
Intensity (earthquake)
A common boundary
where different parts of a system
interact.
interface
discontinuous pattern of
intermittent streams that do not
flow to the ocean
Interior drainage
Compositional category for igneous rocks found
near the middle of Bowen’s reaction
series, mainly amphibole and the
intermediate plagioclase feldspars.
Intermediate
earthquake focus at a depth of
between 60 and 300 kilometers
Intermediate focus
process such as mountain building or volcanism
that derives its energy from Earth’s
interior and elevates Earth’s surface.
Internal process
Igneous activity that occurs within a tectonic
plate away from plate boundaries.
Intraplate volcanism
Igneous rock that
formed below Earth’s surface
Intrusive rock
An atom or molecule that
possesses an electrical charge
Ion
A chemical bond
between two oppositely charged
ions formed by the transfer of
valence electrons from one atom to
another.
Ionic Bond
The concept that Earth’s
crust is floating in gravitational
balance upon the material of the
mantle.
Isostasy
fracture in rock along
which there has been no movement.
joint
A steep-sided hill,
composed of sand and gravel,
originating when sediment collected
in openings in stagnant glacial ice
kame
A narrow,
terracelike mass of stratified drift
deposited between a glacier and an
adjacent valley wall.
kame terrace
A topography consisting of
numerous depressions called
sinkholes.
karst
Depressions created
when blocks of ice become lodged
in glacial deposits and subsequently
melt.
kettle holes
A massive, concordant
igneous body intruded between
preexisting strata
laccolith
Mudflows on the slopes of
volcanoes that result when unstable
layers of ash and debris become
saturated and flow downslope,
usually following stream channels.
lahar
The movement of
water particles in straight-line paths
that are parallel to the channel. The
water particles move downstream
without mixing.
Laminar flow
A ridge of till
along the sides of a valley glacier
composed primarily of debris that
fell to the glacier from the valley
walls.
Lateral moraine
A red, highly leached soil
type found in the tropics and rich in
oxides of iron and aluminum.
Laterite
The northern portion of
Pangaea consisting of North
America and Eurasia.
Laurasia
Magma that reaches Earth’s
surface.
Lava
A bulbous mass
associated with an old-age
volcano, produced when thick lava
is slowly squeezed from the vent.
Lava domes may act as plugs to
deflect subsequent gaseous
eruptions.
Lava dome
Tunnel in hardened lava that acts as a horizontal conduit for lava flowing from a volcanic vent. Lava tubes allow fluid lavas to advance great distances.
Lava tube
In any undeformed sequence of sedimentary rocks or surface-deposited igneous materials, each layer is older than the one above it and younger than the one below.
Law of superposition
The depletion of soluble materials from the upper soil by downward-percolating water.
Leaching
Silicate minerals that lack iron and/or magnesium. They are generally lighter in color and have lower specific gravities than dark silicates.
Light silicate
The process, generally by cementation and/or compaction, of converting sediments to solid rock.
Lithification
The rigid outer layer of Earth, including the crust and upper mantle.
Lithosphere
A coherent unit of Earth’s rigid outer layer that includes the crust and upper mantle.
Lithospheric plate
See Temporary (local) base level.
Local (temporary) base level
Deposits of windblown silt, lacking visible layers, generally buff colored, and capable of maintaining a nearly vertical cliff.
Loess
Long ridges of sand oriented parallel to the prevailing wind; these dunes form where sand supplies are limited.
Longitudinal dunes
A cross section of a stream channel along its descending course from the head to the mouth.
Longitudinal profile
A nearshore current that flows parallel to the shore.
Longshore current
Streams that lose water to the groundwater system by outflow through the streambed.
Losing stream
The part of the mantle that extends from a depth of 660 kilometers (410 miles) to the top of the core, at a depth of 2900 kilometers (1800 miles).
Lower mantle
The appearance or quality of light reflected from the surface of a mineral.
Luster
Because basaltic rocks contain a high percentage of ferromagnesian minerals, they are also called mafic (from magnesium and ferrum, the Latin name for iron).
Mafic
A body of molten rock found at depth, including any dissolved gases and crystals.
Magma
A change in Earth’s magnetic field from normal to reverse or vice versa.
Magnetic reversal
The detailed history of Earth’s magnetic reversals developed by establishing the magnetic polarity of lava flows of known age.
Magnetic time scale
A sensitive instrument used to measure the intensity of Earth’s magnetic field at various points.
Magnetometer
The total amount of energy released during an earthquake.
Magnitude (earthquake)
A type of hydrogenous sediment scattered on the ocean floor, consisting mainly of manganese and iron, and usually containing small amounts of copper, nickel, and cobalt.
Manganese nodules
The 2885-kilometer (1789-mile) thick layer of Earth located below the crust.
Mantle
A mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core–mantle boundary.
Mantle plume
The sum of the number of neutrons and protons in the nucleus of an atom.
Mass number
The downslope movement of rock, regolith, and soil under the direct influence of gravity.
Mass wasting
An igneous pluton that is not tabular in shape.
Massive
A looplike bend in the course of a stream.
Meander
A floodplain feature created when an oxbow lake becomes filled with sediment.
Meander scar
The physical disintegration of rock, resulting in smaller fragments.
Mechanical weathering
A ridge of till formed when lateral moraines from two coalescing valley glaciers join.
Medial moraine
The liquid portion of magma excluding the solid crystals.
Melt
A time span on the geologic time scale between the Paleozoic and Cenozoic eras—from about 251 million to 65.5 million years ago.
Mesozoic era
A chemical bond present in all metals that may be characterized as an extreme type of electron sharing in which the electrons move freely from atom to atom.
Metallic bond
Rock formed by the alteration of preexisting rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids.
Metamorphic rock
The changes in mineral composition and texture of a rock subjected to high temperature and pressure within Earth.
Metamorphism
A significant change in the chemical composition of a rock, usually by the addition or removal of ions in solution.
Metasomatism
Relatively small fragments of continental crust that may lie above sea level, such as the island of Madagascar, or be submerged, as exemplified by the Campbell Plateau located on the seafloor near New Zealand.
Microcontinents
See Oceanic ridge.
Mid-ocean ridge
A rock exhibiting both igneous and metamorphic rock characteristics. Such rocks may form when light-colored silicate minerals melt and then crystallize, while the dark silicate minerals remain solid.
Migmatite
A naturally occurring, inorganic crystalline material with a unique chemical structure.
Mineral
All discovered and undiscovered deposits of a useful mineral that can be extracted now or at some time in the future.
Mineral resource
A 12-point scale developed to evaluate earthquake intensity based on the amount of damage to various structures.
Modified Mercalli intensity scale
The boundary separating the crust and the mantle, discernible by an increase in seismic velocity.
Mohorovičić discontinuity (Moho)
A series of 10 minerals used as a standard in determining hardness.
Mohs scale
A more precise measure of earthquake magnitude than the Richter scale, it is derived from the amount of displacement that occurs along a fault zone.
Moment magnitude
A one-limbed flexure in strata. The strata are usually flat-lying or very gently dipping on both sides of the monocline.
Monocline
The point downstream where a river empties into another stream or water body.
Mouth
A feature in some sedimentary rocks that forms when wet mud dries out, shrinks, and cracks.
Mud crack
See Debris flow.
Mudflow
The elevated landforms composed of alluvium that parallel some streams and act to confine their waters, except during flood stage.
Natural levees
The lowest tidal range, occurring near the times of the first and third quarters of the Moon.
Neap tide
The zone of a beach that extends from the low-tide shoreline seaward to where waves break at low tide.
Nearshore zone
A model for the origin of the solar system that assumes a rotating nebula of dust and gases that contracted to produce the Sun and planets.
Nebular theory
As used in climate change, any effect that is opposite of the initial change and tends to offset it.
Negative feedback mechanism
A subatomic particle found in the nucleus of an atom. The neutron is electrically neutral, with a mass approximately equal to that of a proton.
Neutron
A term for the texture of sedimentary rocks in which the minerals form a pattern of interlocking crystals.
Nonclastic
An unconformity in which older metamorphic or intrusive igneous rocks are overlain by younger sedimentary strata.
Nonconformity
See Light silicate.
Nonferromagnesian silicate
Metamorphic rocks that do not exhibit foliation.
Nonfoliated texture
Mineral resource that is not a fuel or processed for the metals it contains.
Nonmetallic mineral resource
Resource that forms or accumulates over such long time spans that it must be considered as fixed in total quantity.
Nonrenewable resource
A fault in which the rock above the fault plane has moved down relative to the rock below.
Normal fault
A magnetic field the same as that which presently exists.
Normal polarity
The small, heavy core of an atom that contains all of its positive charge and most of its mass.
Nucleus
Incandescent volcanic debris that is buoyed up by hot gases and moves downslope in an avalanche fashion.
Nuée ardente
Date that specifies the actual number of years that have passed since an event occurred.
Numerical date
An extensive region on the ocean floor composed of thick accumulations of pillow basalts and other mafic rocks that in some cases exceed 30 kilometers in thickness.
Oceanic plateau
A continuous mountainous ridge on the floor of all the major ocean basins and varying in width from 500 to 5000 kilometers (300 to 3000 miles). The rifts at the crests of these ridges represent divergent plate boundaries.
Oceanic ridge
Atoms combine in order that each may have the electron arrangement of a noble gas; that is, the outer energy level contains eight electrons.
Octet rule
The relatively flat submerged zone that extends from the breaker line to the edge of the continental shelf.
Offshore zone
A geologic structure that allows for significant amounts of oil and gas to accumulate.
Oil trap
Usually a useful metallic mineral that can be mined at a profit. The term is also applied to certain nonmetallic minerals such as fluorite and sulfur.
Ore
Sedimentary rock composed of organic carbon from the remains of plants that died and accumulated on the floor of a swamp. Coal is the primary example.
Organic sedimentary rock
Layers of sediment are generally deposited in a horizontal or nearly horizontal position.
Original horizontality
The processes that collectively result in the formation of mountains.
Orogenesis
A layer beneath the mantle about 2270 kilometers (1410 miles) thick that has the properties of a liquid.
Outer core
The release of gases dissolved in molten rock.
Outgassing
A tongue of ice normally flowing rapidly outward from an ice cap or ice sheet, usually through mountainous terrain to the sea.
Outlet glacier
A relatively flat, gently sloping plain consisting of materials deposited by meltwater streams in front of the margin of an ice sheet.
Outwash plain
A curved lake produced when a stream cuts off a meander.
Oxbow lake
The removal of one or more electrons from an atom or ion. So named because elements commonly combine with oxygen.
Oxidation
A method of deciphering past temperatures based on the precise measurement of the ratio between two isotopes of oxygen, 16O and 18O. Analysis is commonly made of seafloor sediments and cores of glacial ice.
Oxygen isotope analysis
The fastest earthquake wave; travels by compression and expansion of the medium.
P wave
A lava flow with a smooth-to-ropy surface.
Pahoehoe
The study of ancient climates; the study of climate and climate change prior to the period of instrumental records using proxy data.
Paleoclimatology
The natural remnant magnetism in rock bodies. The permanent magnetization acquired by rock that can be used to determine the location of the magnetic poles and the latitude of the rock at the time it became magnetized.
Paleomagnetism
The systematic study of fossils and the history of life on Earth.
Paleontology
A time span on the geologic time scale between the Proterozoic and Mesozoic eras–from about 542 million to 251 million years ago.
Paleozoic era
The proposed supercontinent that 200 million years ago began to break apart and form the present landmasses.
Pangaea
A sand dune similar in shape to a barchan dune except that its tips point into the wind. These dunes often form along coasts that have strong onshore winds, abundant sand, and vegetation that partly covers the sand.
Parabolic dune
Theory that is held with a very high degree of confidence and is comprehensive in scope.
Paradigm
A volcanic cone that forms on the flank of a larger volcano.
Parasitic cone
The material upon which a soil develops.
Parent material
The rock from which a metamorphic rock formed.
Parent rock
The process by which most igneous rocks melt. Because individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results.
Partial melting
A margin that consists of a continental shelf, continental slope, and continental rise. They are not associated with plate boundaries and therefore experience little volcanism and few earthquakes.
Passive continental margin
A chain of small lakes in a glacial trough that occupy basins created by glacial erosion.
Pater noster lakes
A very coarse-grained igneous rock (typically granite) commonly found as a dike associated with a large mass of plutonic rock that has smaller crystals. Crystallization in a water-rich environment is believed to be responsible for the very large crystals.
Pegmatite
A texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in diameter.
Pegmatitic texture
A localized zone of saturation above the main water table created by an impermeable layer (aquitard).
Perched water table
An igneous rock of ultramafic composition thought to be abundant in the upper mantle.
Peridotite
A basic unit of the geologic calendar that is a subdivision of an era. Periods may be divided into smaller units called epochs.
Period
The tabular arrangement of the elements according to atomic number.
Periodic table
Any permanently frozen subsoil. Usually found in the subarctic and arctic regions.
Permafrost
A measure of a material’s ability to transmit water.
Permeability
An igneous rock texture in which the crystals are roughly equal in size and large enough so that individual minerals can be identified with the unaided eye.
Phaneritic texture
That part of geologic time represented by rocks containing abundant fossil evidence. The eon extending from the end of the Proterozoic eon (about 540 million years ago) to the present.
Phanerozoic eon
Conspicuously large crystals in a porphyry that are embedded in a matrix of finer-grained crystals (the groundmass).
Phenocryst
A major division of geology that examines the materials of Earth and seeks to understand the processes and forces acting upon Earth’s surface from below.
Physical geology
A glacier that forms when one or more valley glaciers emerge from the confining walls of mountain valleys and spread out to create a broad sheet in the lowlands at the base of the mountains.
Piedmont glacier
Basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows.
Pillow lava
A vertical conduit through which magmatic materials have passed.
Pipe
Deposit formed when heavy minerals are mechanically concentrated by currents, most commonly streams and waves. Placers are sources of gold, tin, platinum, diamonds, and other valuable minerals.
Placer
A solid celestial body that accumulated during the first stages of planetary formation. Planetesimals aggregated into increasingly larger bodies, ultimately forming the planets.
Planetesimal
Permanent deformation that results in a change in size and shape through folding or flowing.
Plastic deformation
A type of glacial movement that occurs within the glacier, below a depth of approximately 50 meters, in which the ice is not fractured.
Plastic flow
The theory that proposes Earth’s outer shell consists of individual plates, which interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself.
Plate tectonics
The flat central area of an undrained desert basin.
Playa
A temporary lake in a playa.
Playa lake
An epoch of the Quaternary period beginning about 1.8 million years ago and ending about 10,000 years ago. Best known as a time of extensive continental ice sheets.
Pleistocene epoch
The process by which pieces of bedrock are lifted out of place by a glacier.
Plucking
A structure that results from the emplacement and crystallization of magma beneath Earth’s surface.
Pluton
A lake formed during a period of increased rainfall. For example, this occurred in many non-glaciated areas during periods of ice advance elsewhere.
Pluvial lake
A crescent-shaped accumulation of sand and gravel deposited on the inside of a meander.
Point bar
As the result of paleomagnetic studies in the 1950s, researchers proposed that either the magnetic poles migrated greatly through time or the continents gradually shifted their positions.
Polar wandering hypothesis
The process of linking the same molecules together to form a chain or three-dimensional structure.
Polymerization
Two or more minerals having the same chemical composition but different crystalline structures, exemplified by the diamond and graphite forms of carbon.
Polymorphs
The volume of open spaces in rock or soil.
Porosity
An igneous rock texture characterized by two distinctively different crystal sizes. The larger crystals are called phenocrysts, and the matrix of smaller crystals is termed the groundmass.
Porphyritic texture
A texture of metamorphic rocks in which particularly large grains (porphyroblasts) are surrounded by a fine-grained matrix of other minerals.
Porphyroblastic texture
An igneous rock with a porphyritic texture.
Porphyry
As used in climate change, any effect that acts to reinforce the initial change.
Positive-feedback mechanism
A depression formed in a stream channel by the abrasive action of the water’s sediment load.
Pothole
All geologic time prior to the Paleozoic era.
Precambrian
Fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content.
Principle of fossil succession
Layers of sediment are generally deposited in a horizontal or nearly horizontal position.
Principle of original horizontality
The eon following the Archean and preceding the Phanerozoic. It extends between 2.5 billion and 542 million years ago.
Proterozoic eon
A positively charged subatomic particle found in the nucleus of an atom.
Proton
A developing planetary body that grows by the accumulation of planetesimals.
Protoplanet
Data gathered from natural recorders of climate variability such as tree rings, ice
cores, pollen, and ocean-floor
sediments.
Proxy data
A highly heated mixture, largely of ash and pumice fragments, traveling down the flanks of a volcano or along the surface of the ground.
Pyroclastic flow
The volcanic rock ejected during an eruption. Pyroclastics include ash, bombs, and blocks.
Pyroclastic material
An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent eruption.
Pyroclastic texture
The removal of loosened blocks from the bed of a channel during times of high flow rates.
Quarrying
A system of streams running in all directions away from a central elevated structure, such as a volcano.
Radial drainage pattern
The spontaneous decay of certain unstable atomic nuclei.
Radioactivity
The radioactive isotope of carbon produced continuously in the atmosphere and used in dating events as far back as 75,000 years.
Radiocarbon (carbon-14)
The procedure of calculating the absolute ages of rocks and minerals containing certain radioactive isotopes.
Radiometric dating
A dry area on the lee side of a mountain range; many middle-latitude deserts are of this type.
Rainshadow desert
A part of a stream channel in which the water suddenly begins flowing more swiftly and turbulently because of an abrupt steepening of the gradient.
Rapids
An end moraine formed as the ice front stagnated during glacial retreat.
Recessional moraine
A drainage pattern that develops on jointed or fractured bedrock and is characterized by numerous right-angle bends.
Rectangular pattern
A change in direction of waves as they enter shallow water. The portion of the wave in shallow water is slowed, which causes the wave to bend and align with the underwater contours.
Refraction
Metamorphism associated with large-scale mountain building.
Regional metamorphism
The layer of rock and mineral fragments that nearly everywhere covers Earth’s land surface.
Regolith
Rocks are placed in their proper sequence or order; only the chronological order of events is determined.
Relative dating
A resource that is virtually inexhaustible or that can be replenished over relatively short time spans.
Renewable resource
Already identified deposits from which minerals can be extracted profitably.
Reserve
The porous, permeable portion of an oil trap that yields oil and gas.
Reservoir rock
Soil developed directly from the weathering of the bedrock below.
Residual soil
A fault in which the material above the fault plane moves up in relation to the material below.
Reverse fault
A magnetic field opposite to that which presently exists.
Reverse polarity
A scale of earthquake magnitude based on the motion of a seismograph.
Richter scale
A mechanism that may contribute to plate motion. It involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity.
Ridge push
A region of Earth’s crust along which divergence (separation) is taking place.
Rift
A strong, narrow surface or near-surface current of short duration and high speed that moves seaward through the breaker zone at nearly a right angle to the shore.
Rip current
Small waves of sand that develop on the surface of a sediment layer by the action of moving water or air.
Ripple marks
A general term for a stream that carries a substantial amount of water and has numerous tributaries.
River
An asymmetrical knob of bedrock formed when glacial abrasion smoothes the gentle slope facing the advancing ice sheet and plucking steepens the opposite side as the ice overrides the knob.
Roche moutonnée
A consolidated mixture of minerals.
Rock
The very rapid downslope movement of rock and debris. These rapid movements may be aided by a layer of air trapped beneath the debris, and they have been known to reach speeds in excess of 200 kilometers per hour.
Rock avalanche
The tendency of rock to split along parallel, closely spaced surfaces. These surfaces are often highly inclined to the bedding planes in the rock.
Rock cleavage
A model that illustrates the origin of the three basic rock types and the interrelatedness of Earth’s materials and processes.
Rock cycle
Ground-up rock produced by the grinding effect of a glacier.
Rock flour
The rapid slide of a mass of rock downslope along planes of weakness.
Rockslide
Water that flows over the land rather than infiltrating into the ground.
Runoff
An earthquake wave, slower than a P wave, that travels only in solids.
S wave
A white crust on the ground produced when water evaporates and leaves its dissolved materials behind.
Salt flat
Transportation of sediment through a series of leaps or bounces.
Saltation
A type of foliation characteristic of coarser-grained metamorphic rocks. Such rocks have a parallel arrangement of platy minerals such as the micas.
Schistosity
Hardened lava that has retained the vesicles produced by escaping gases.
Scoria
See Cinder cone.
Scoria cone
An arch formed by wave erosion when caves on opposite sides of a headland unite.
Sea arch
An isolated mass of rock standing just offshore, produced by wave erosion of a headland.
Sea stack
The hypothesis first proposed in the 1960s by Harry Hess, suggesting that new oceanic crust is produced at the crests of mid-ocean ridges, which are the sites of divergence.
Seafloor spreading
An isolated volcanic peak that rises at least 1000 meters (3300 feet) above the deep-ocean floor.
Seamount
