Book Glossary Flashcards - Essentials of Geo P1
1
Q
A type of lava flow that has a
jagged, blocky surface.
A
aa
2
Q
A general term for the
loss of ice and snow from a glacier.
A
Ablation
3
Q
The grinding and
scraping of a rock surface by the
friction and impact of rock particles
carried by water, wind, or ice.
A
Abrasion
4
Q
Very level area of
the deep-ocean floor, usually lying
at the foot of the continental rise
A
Abyssal plain
5
Q
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.
A
Accretionary wedge
6
Q
Usually narrow and consisting of
highly deformed sediments, they
occur where oceanic lithosphere is
being subducted beneath the
margin of a continent.
A
Active continental margin
7
Q
The zone above the
permafrost that thaws in summer
and refreezes in winter.
A
Active layer
8
Q
Tiny solid and liquid
particles suspended in the
atmosphere.
A
Aerosols
9
Q
A smaller earthquake
that follows the main earthquake.
A
Aftershock
10
Q
A stream
channel in which the bed and
banks are composed largely of
unconsolidated sediment (alluvium)
that was previously deposited in the
valley
A
Alluvial channel
11
Q
A fan-shaped deposit
of sediment formed when a stream’s
slope is abruptly reduced.
A
Alluvial fan
12
Q
Unconsolidated
sediment deposited by a stream
A
Alluvium
13
Q
A type of convergent boundary in
which a slab of oceanic crust is
subducting beneath a continental
margin.
A
Andean-type plate margin
14
Q
Igneous rocks having a
mineral makeup between that of
granite and basalt, after the common
volcanic rock andesite.
A
Andesitic
15
Q
The steepest
angle at which loose material
remains stationary without sliding
downslope.
A
Angle of repose
16
Q
An unconformity in which the older
strata dip at an angle different from
that of the younger beds.
A
Angular unconformity
17
Q
A hard, metamorphic
form of coal that burns clean and
hot
A
Anthracite
18
Q
A fold in sedimentary
strata that resembles an arch.
A
Anticline
19
Q
A texture of
igneous rocks in which the crystals
are too small for individual minerals
to be distinguished with the
unaided eye.
A
Aphanitic texture
20
Q
Rock or sediment
through which groundwater moves
easily.
A
Aquifer
21
Q
An impermeable bed
that hinders or prevents
groundwater movement.
A
Aquitard
22
Q
The first eon of
Precambrian time; the eon
preceding the Proterozoic. It
extends between 4.5 and 2.5 billion
years ago.
A
Archean eon
23
Q
A narrow, knifelike ridge
separating two adjacent glaciated
valleys
A
Arête
24
Q
A feldspar-rich sandstone.
A
Arkose
25
A well in which the
water rises above the level where it
was initially encountered
Artesian well
26
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
27
The gaseous portion
of a planet; the planet’s envelope of
air. One of the traditional
subdivisions of Earth’s physical
environment
Atmosphere
28
A continuous or broken ring
of coral reef surrounding a central
lagoon.
Atoll
29
The smallest particle that
exists as an element.
Atom
30
A mass unit
equal to exactly one-twelfth the
mass of a carbon-12 atom
Atomic mass unit
31
The number of
protons in the nucleus of an atom
Atomic number
32
The average of the
atomic masses of isotopes of a given
element.
Atomic weight
33
A zone or halo of contact
metamorphism found in the host
rock surrounding an igneous
intrusion
Aureole
34
A poorly drained
area on a floodplain, resulting when
natural levees are present.
Back swamp
35
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
36
An apron of sediment
along a mountain front created by
the coalescence of alluvial fans
Bajada
37
Finely
layered iron- and silica-rich (chert)
layers deposited mainly during the
Precambrian
Banded iron formations
38
Common term for sand and
gravel deposits in a stream channel.
-Bar
-Channel
-Alluvium
Bar
39
A solitary sand
dune shaped like a crescent with its
tips pointed downwind
Barchan dune
40
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
41
A low, elongated
ridge of sand that parallels the coast.
Barrier island
42
A mechanism of glacial
movement in which the ice mass
slides over the surface below
Basal slip
43
An aphanitic igneous rock
of mafic composition.
Basalt
44
Term used to describe
igneous rocks that contain abundant
dark (ferromagnesian) minerals and
about 50 percent silica.
Basaltic
45
The level below which
a stream cannot erode
Base level
46
A circular downfolded
structure.
Basin
47
A large mass of igneous
rock that formed when magma was
emplaced at depth, crystallized, and
was subsequently exposed by
erosion.
Batholith
48
A sandbar that
completely crosses a bay, sealing it
off from the main body of water
Baymouth bar
49
An accumulation of
sediment found along the landward
margin of the ocean or a lake
Beach
50
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
51
The wet, sloping
surface that extends from the berm
to the shoreline
Beach face
52
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
53
Sediment rolled along
the bottom of a stream by moving
water, or particles rubbed along the
ground surface by wind.
Bed load
54
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
55
A general term for the
rock that underlies soil or other
unconsolidated surface materials.
Bedrock
56
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
57
The dry, gently sloping zone
on the backshore of a beach at the
foot of the coastal cliffs or dunes
Berm
58
Describing a type of
chemical sediment that forms when
material dissolved in water is
precipitated by water-dwelling
organisms. Shells are common
examples.
Biochemical
59
Seafloor
sediments consisting of material of
marine-organic origin.
Biogenous sediment
60
The most
common form of coal, often called
soft, black coal.
Bituminous coal
61
Lava having a surface
of angular blocks associated with
material having andesitic and
rhyolitic compositions.
Block lava
62
A depression excavated by wind in
easily eroded materials.
Blowout (deflation hollow)
63
A seismic wave that
travels through Earth’s interior
Body wave
64
A layer of fine sediment deposited beyond the
advancing edge of a delta and then
buried by continuous delta growth.
Bottomset bed
65
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
66
A stream consisting of numerous intertwining
channels.
Braided stream
67
A structure protecting a nearshore area from
breaking waves.
Breakwater
68
A sedimentary rock
composed of angular fragments that
were lithified.
Breccia
69
Deformation
that involves the fracturing of rock.
Associated with rocks near the
surface.
Brittle deformation
70
Lowgrade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata.
- Zeolite Facies
- Diagenesis
- Burial Metamorphism
Burial metamorphism
71
A large depression
typically caused by collapse of the
summit area of a volcano following
a violent eruption.
Caldera
72
A hard layer, rich in
calcium carbonate, that forms
beneath the B horizon in soils of arid
regions.
Caliche
73
Wastage of a glacier that
occurs when large pieces of ice
break off into water.
Calving
74
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
75
The total amount of
sediment a stream is able to
transport
Capacity
76
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
77
The concept that
Earth was shaped by catastrophic
events of a short-term nature.
Catastrophism
78
A naturally formed
underground chamber or series of
chambers most commonly
produced by solution activity in
limestone.
Cavern
79
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
80
A time span on the
geologic time scale beginning about
65.5 million years ago following the
Mesozoic era.
Cenozoic era
81
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
82
Sedimentary rock consisting of
material that was precipitated from
water by either inorganic or organic
means.
Chemical sedimentary rock
83
The processes by which the internal
structure of a mineral is altered by
the removal and/or addition of
elements.
Chemical weathering
84
A rather small
volcano built primarily of pyroclastics
ejected from a single vent.
Cinder cone
85
An amphitheater-shaped
basin at the head of a glaciated
valley produced by frost wedging
and plucking.
Cirque
86
A sedimentary rock
texture consisting of broken
fragments of preexisting rock.
Clastic
87
The tendency of a
mineral to break along planes of
weak bonding.
Cleavage
88
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
89
The exchanges of
energy and moisture occurring
among the atmosphere,
hydrosphere, geosphere, biosphere,
and cryosphere.
Climate system
90
A strip of land that
extends inland from the coastline
as far as ocean-related features can
be found.
Coast
91
The coast’s seaward
edge; the landward limit of the effect
of the highest storm waves on the
shore.
Coastline
92
A pass between mountain
valleys where the headwalls of two
cirques intersect.
Col
93
A phenomenon of light by
which otherwise identical objects
may be differentiated.
Color
94
A feature found in caves
that is formed when a stalactite and
stalagmite join.
-Column
-spleothoems
-travertine deposits
Column
95
A pattern of
cracks that forms during cooling of
molten rock to generate columns
Columnar joints
96
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
97
A measure of the
largest particle a stream can transport;
a factor dependent on velocity.
Competence
98
A volcano
composed of both lava flows and
pyroclastic material.
Composite Cone
99
Mountains in which great horizontal
forces have shortened and
thickened the crust. Most major
mountain belts are of this type.
Compressional Mountains
100
A term used to
describe intrusive igneous masses
that form parallel to the bedding of
the surrounding rock.
Concordant
101
A pipelike opening
through which magma moves
toward Earth’s surface. It terminates
at a surface opening called a vent.
Conduit
102
An aquifer that
has impermeable layers (aquitards)
both above and below.
Confined
103
A coneshaped
depression immediately
surrounding a well.
Cone of depression
104
Rock layers
that were deposited without
interruption.
Conformable layers
105
A sedimentary
rock consisting of rounded,
gravel-size particles.
Conglomerate
106
Changes in rock caused by the heat
of a nearby magma body.
Contact Metamorphism
107
A hypothesis,credited largely to Alfred Wegener,
that suggested all present continents
once existed as a single
supercontinent.
Continental Drift
108
A linear zone
along which continental lithosphere
stretches and pulls apart. Its creation
may mark the beginning of a new
ocean basin.
Continental rift
109
The gently
sloping surface at the base of the
continental slope.
Continental Rise
110
The gently
sloping submerged portion of the
continental margin, extending from
the shoreline to the continental
slope
Continental shelf
111
The steep
gradient that leads to the deepocean
floor and marks the seaward
edge of the continental shelf.
Continental slope
112
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
113
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
114
Located beneath the mantle,
it is Earth’s innermost layer. The
core is divided into an outer core
and an inner core.
Core
115
Establishing the
equivalence of rocks of similar age
in different areas.
Correlation
116
A chemical bond produced by the sharing of
electrons.
Covalent bond
117
The depression at the
summit of a volcano, or that which
is produced by a meteorite impact
Crater
118
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
119
The slow downhill
movement of soil and regolith.
Creep
120
A deep crack in the
brittle surface of a glacier.
Crevasse
121
Structure in which
relatively thin layers are inclined at
an angle to the main bedding.
Formed by currents of wind or water.
Cross-bedding
122
A principle of
relative dating. A rock or fault is
younger than any rock (or fault)
through which it cuts.
Cross-cutting
123
The very thin, outermost
layer of Earth
Crust
124
An orderly arrangement
of atoms
Crystal
125
The formation
and growth of a crystalline solid
from a liquid or gas
Crystallization
126
The temperature
above which a material loses its
magnetization.
Curie point
127
The area of active
erosion on the outside of a meander.
Cut bank
128
A short channel segment
created when a river erodes through
the narrow neck of land between
meanders.
Cutoff
129
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
130
An isotope resulting from radioactive decay.
Daughter product
131
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
132
Melting that occurs as rock ascends due to a
drop in confining pressure
Decompression melting
133
An earthquake focus at a depth of more
than 300 kilometers.
Deep-focus earthquake
134
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
135
The lifting and removal
of loose material by wind.
Deflation
136
General term for
the processes of folding, faulting,
shearing, compression, or extension
of rocks as the result of various
natural forces
Deformation
137
An accumulation of
sediment formed where a stream
enters a lake or ocean
Delta
138
A stream system that resembles the
pattern of a branching tree.
Dendritic drainage pattern
139
The weight per unit
volume of a particular material.
Density
140
One of the two types of
dry climate; the drier of the dry
climates.
Desert
141
A layer of coarse pebbles and gravel created when wind removes the finer
material.
Desert pavement
142
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
143
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
144
A collective term for
all the chemical, physical, and
biological changes that take place
after sediments are deposited and
during and after lithification.
Diagenesis
145
A tabular-shaped intrusive
igneous feature that cuts through
the surrounding rock.
Dike
146
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
147
A fault in which
the movement is parallel to the dip
of the fault.
Dip-slip fault
148
The quantity of water in a stream that passes a given point
in a given period of time.
Discharge
149
A type of unconformity in which the beds
above and below are parallel
Disconformity
150
A sudden change
with depth in one or more of the
physical properties of the material
making up Earth’s interior
Discontinuity
151
The boundary between two dissimilar
materials in Earth’s interior as
determined by the behavior of
seismic waves.
152
A term used to
describe plutons that cut across
existing rock structures, such as
bedding planes.
Discordant
153
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
154
The portion of a
stream’s load carried in solution.
Dissolved load
155
A section of a stream
that leaves the main flow.
Distributary
156
A tide characterized
by a single high and low water
height each tidal day.
Diurnal tide
157
A boundary in which two plates move
apart, resulting in upwelling of
material from the mantle to create
new seafloor.
Divergent plate boundary
158
An imaginary line that
separates the drainage of two
streams; often found along a ridge.
Divide
159
A roughly circular,
upfolded structure.
Dome
160
The land area
that contributes water to a stream.
Drainage basin
161
The difference in
height between the bottom of a cone
of depression and the original height
of the water table.
Drawdown
162
A streamlined
asymmetrical hill composed of
glacial till. The steep side of the hill
faces the direction from which the
ice advanced.
Drumlin
163
A climate in which
the yearly precipitation is less than
the potential loss of water by
evaporation.
Dry Climate
164
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
165
A hill or ridge of
wind-deposited sand.
Dune
166
The downslope
movement of water-saturated,
clay-rich sediment, most
characteristic of humid regions
Earthflow
167
The vibration of
Earth produced by the rapid release
of energy.
Earthquake
168
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
169
Nonpermanent deformation in
which rock returns to its original
shape when the stress is released.
Elastic deformation
170
The sudden
release of stored strain in rocks that
results in movement along a fault
Elastic rebound
171
The washing out of
fine soil components from the A
horizon by downward-percolating
water.
Eluviation
172
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
173
A ridge of till
marking a former position of the
front of the glacier.
End moraine
174
Spherically shaped
negatively charged zones that
surround the nucleus of an atom
Energy levels
175
The largest time unit on the
geologic time scale, next in order of
magnitude above era.
Eon
176
The location on Earth’s
surface that lies directly above the
focus of an earthquake.
Epicenter
177
A unit of the geological
time scale that is a subdivision of a
period.
Epoch
178
A major division on the
geologic time scale; are divided
into shorter units called periods.
Eras
179
The incorporation and
transportation of material by a
mobile agent, such as water, wind,
or ice.
Erosion
180
Buoyant plumes of hot ash-laden gases that
can extend thousands of meters into
the atmosphere
Eruption column
181
Sinuous ridge composed
largely of sand gravel deposited
by a stream flowing in a tunnel
beneath a glacier near its
terminus.
Esker
182
A partially enclosed
coastal water body that is connected
to the ocean. Salinity here is
measurably reduced by the
freshwater flow of rivers.
Estuary
183
Organisms whose
genetic material is enclosed in a
nucleus. Plants, animals, and fungi
are eukaryotes.
Eukaryotes
184
A sedimentary rock
formed of material deposited from
solution by evaporation of water
Evaporite
185
The combined effect of evaporation and
transpiration.
Evapotranspiration
186
Large, dome-shaped structure, usually
composed of granite, formed by
sheeting.
Exfoliation dome
187
A permanent stream that traverses a desert and
has its source in well-watered areas
outside the desert.
Exotic stream
188
Process such as weathering, mass wasting, or
erosion that is powered by the Sun
and transforms solid rock into
sediment.
External process
189
Igneous activity that
occurs at Earth’s surface.
Extrusive
190
A zone of scattered clouds
and calm averaging about 20
kilometers in diameter at the center
of a hurricane.
Eye
191
A doughnut-shaped area
of intense cumulonimbus
(thunderstorm) development and
very strong winds that surrounds
the eye of a hurricane.
Eye wall
192
A type of movement
common to mass-wasting processes
that refers to the free falling of
detached individual pieces of any
size.
Fall
193
A break in a rock mass
along which movement has
occurred.
Fault
194
Slow, gradual
displacement along a fault that
occurs relatively smoothly and with
little noticeable seismic activity.
Fault creep
195
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
196
A mountain formed by the
displacement of rock along a fault.
Fault-block mountain
197
A term derived from
feldspar and silica (quartz). It is a
term used to describe granitic
igneous rocks.
Felsic
198
The distance that the wind
has traveled across the open water.
Fetch
199
A steep-sided inlet of the
sea formed when a glacial trough
was partially submerged.
Fjord
200
A crack in rock along
which there is a distinct separation.
Fissure
201
An eruption in
which lava is extruded from narrow
fractures or cracks in the crust.
Fissure eruption
202
The overflow of a stream
channel that occurs when discharge
exceeds the channel’s capacity. The
most common and destructive
geologic hazard.
Flood
203
Flows of basaltic
lava that issue from numerous
cracks or fissures and commonly
cover extensive areas to thicknesses
of hundreds of meters.
Flood basalts
204
The flat, low-lying
portion of a stream valley subject to
periodic inundation.
Floodplain
205
A type of movement
common to mass-wasting processes
in which water-saturated material
moves downslope as a viscous fluid.
Flow
206
The absorption of
ultraviolet light, which is reemitted
as visible light.
Fluorescence
207
The zone
within Earth where rock
displacement produces an
earthquake.
Focus (earthquake)
208
A bent layer or series of
layers that were originally horizontal
and subsequently deformed.
Fold
209
A texture of
metamorphic rocks that gives the
rock a layered appearance.
Foliated
210
A term for a linear
arrangement of textural features
often exhibited by metamorphic
rocks.
Folation
211
An inclined bed
deposited along the front of a delta.
Foreset bed
212
Small earthquakes
that often precede a major
earthquake.
Foreshocks
213
That portion of the
shore lying between the normal
high- and low-water marks; the
intertidal zone.
Foreshore
214
The remains or traces of
organisms preserved from the
geologic past.
Fossil
215
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
216
Fossil organisms succeed one another in a
definite and determinable order, and
any time period can be recognized
by its fossil content.
Fossil succession
217
The
process that separates magma into
components having varied
compositions and melting points.
Fractional crystallization
218
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)
219
Any break or
rupture in rock along which no
appreciable movement has taken
place.
Fracture (rock)
220
Linear zone of
irregular topography on the
deep-ocean floor; it follows
transform faults and their inactive
extensions.
Fracture zone
221
The mechanical
breakup of rock caused by the
expansion of freezing water in
cracks and crevices.
Frost wedging
222
A vent in a volcanic
area from which fumes or gases
escape.
Fumarole
223
Streams that gain
water from the inflow of
groundwater through the
streambed.
Gaining stream
224
The science that
examines Earth, its form and
composition, and the changes
it has undergone and is
undergoing.
Geology
225
The solid Earth; one
of Earth’s four basic spheres.
Geosphere
226
Natural steam used for power generation.
Geothermal energy
227
The gradual increase in temperature
with depth in the crust. The average
is 30 °C per kilometer in the
upper crust.
Geothermal gradient
228
A fountain of hot water
ejected periodically from the
ground.
Geyser
229
The balance, or
lack of balance, between
accumulation at the upper end
of a glacier and loss at the
other end.
Glacial budget
230
An all-embracing
term for sediments of glacial origin,
no matter how, where, or in what
shape they were deposited.
Glacial drift
231
An ice-transported boulder that was not
derived from the bedrock near its
present site.
Glacial erratic
232
Scratches and
grooves on bedrock caused by
glacial abrasion.
Glacial striations
233
A mountain valley
that has been widened, deepened,
and straightened by a glacier.
Glacial trough
234
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
235
Natural glass
produced when molten lava cools
too rapidly to permit crystallization.
Volcanic glass is a solid composed of
unordered atoms.
Volcanic Glass
236
A term used to
describe the texture of certain
igneous rocks, such as obsidian, that
contain no crystals.
Glassy texture
237
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
238
The southern
portion of Pangaea consisting of
South America, Africa, Australia,
India, and Antarctica.
Gondwanaland
239
A valley formed by the
downward displacement of a
fault-bounded block.
Graben
240
A sediment layer
characterized by a decrease in
sediment size from bottom to top.
Graded bed
241
A stream that has
the correct channel characteristics to
maintain the exact velocity required
to transport the material supplied
to it.
Graded stream
242
The slope of a stream;
generally measured in feet per mile.
Gradient
243
Igneous rocks composed
mainly of light-colored silicates
(quartz and feldspar) are said to
have this composition.
Granitic
244
The gradual subsidence of mountains
caused by lateral spreading of weak
material located deep within these
structures.
Gravitational collapse
245
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
246
A short wall built at a right
angle to the seashore to trap moving
sand.
Groin
247
An undulating layer of till deposited as the ice front retreats
- Tillites
- Ground Moraine
- Cirque
Ground moraine
248
The **matrix** of smaller crystals within an igneous rock that has porphyritic texture.
Groundmass
249
Water in the **zone of saturation**
Groundwater
250
A submerged flat-topped seamount.
-Guyot
-Ridge
-Abbysal plain
Guyot
251
The common or characteristic shape of a crystal or aggregate of crystals.
-Form
-Habit
-Crystal
Habit
252
An informal term that refers to the **earliest interval(eon)** of Earth history—before the oldest known rocks.
Hadeon Eon
253
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
254
The time required for
one half of the atoms of a radioactive
substance to decay.
Half-life
255
A tributary valley that enters a glacial trough at a considerable height above the floor of the trough.
-Hanging Valley
-Waterfall
-Drumlin
Hanging valley
256
A mineral’s resistance to
scratching and abrasion.
Hardness
257
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
258
The extension
upslope of the head of a valley due
to erosion
Headward erosion
259
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
260
A narrow, sharp-crested
ridge formed by the upturned edge
of a steeply dipping bed of resistant
rock.
Hogback
261
A pyramidlike peak formed
by glacial action in three or more
cirques surrounding a mountain
summit
Horn
262
An elongated, uplifted
block of crust bounded by faults
Horst
263
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
264
A chain of
volcanic structures produced as a
lithospheric plate moves over a
mantle plume.
Hot Spot Track
265
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
266
Organic matter in soil
produced by the decomposition of
plants and animals.
Humus
267
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
268
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
269
Seafloor sediments consisting of minerals
that crystallize from seawater. The
principal example is manganese
nodules.
Hydrogenous sediment
270
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
271
A chemicalweathering
process in which
minerals are altered by chemically
reacting with water and acids.
Hydrolysis
272
The water portion
of our planet; one of the traditional
subdivisions of Earth’s physical
environment.
Hydrosphere
273
Chemical alterations that occur as
hot, ion-rich water circulates
through fractures in rock.
Hydrothermal metamorphism
274
The hot, watery solution that escapes from a mass of magma during the latter stages of crystallization.
Hydrothermal solution
275
A tentative explanation that is then tested to
determine if it is valid.
Hypothesis
276
A mass of glacial ice
covering a high upland or plateau
and spreading out radially
Ice Cap
277
A very large, thick mass
of glacial ice flowing outward in all
directions from one or more
accumulation centers
Ice Sheet
278
An accumulation of stratified drift
deposited in contact with a
supporting mass of ice.
Ice-contact deposit
279
A rock formed by
the crystallization of molten magma.
Igneous rock
280
A soil lacking horizons.
Immature Soil
281
Metamorphism that occurs when
meteorites strike Earth’s surface
Impact metamorphism
282
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
283
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
284
A fossil that is
associated with a particular span of
geologic time
Index fossil
285
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
286
The movement of
surface water into rock or soil
through crack and pore spaces.
Infiltration
287
The maximum rate at which soil can
absorb water.
Infiltration capacity
288
The solid, innermost
layer of Earth, about 1216
kilometers (754 miles) in radius.
Inner core
289
An isolated mountain
remnant characteristic of the late
stage of erosion in a mountainous
region
Inselberg
290
measure of the degree of earthquake
shaking at a given locale based on
the amount of damage.
Intensity (earthquake)
291
A common boundary
where different parts of a system
interact.
interface
292
discontinuous pattern of
intermittent streams that do not
flow to the ocean
Interior drainage
293
Compositional category for igneous rocks found
near the middle of Bowen’s reaction
series, mainly amphibole and the
intermediate plagioclase feldspars.
Intermediate
294
earthquake focus at a depth of
between 60 and 300 kilometers
Intermediate focus
295
process such as mountain building or volcanism
that derives its energy from Earth’s
interior and elevates Earth’s surface.
Internal process
296
Igneous activity that occurs within a tectonic
plate away from plate boundaries.
Intraplate volcanism
297
Igneous rock that
formed below Earth’s surface
Intrusive rock
298
An atom or molecule that
possesses an electrical charge
Ion
299
A chemical bond
between two oppositely charged
ions formed by the transfer of
valence electrons from one atom to
another.
Ionic Bond
300
The concept that Earth’s
crust is floating in gravitational
balance upon the material of the
mantle.
Isostasy
301
fracture in rock along
which there has been no movement.
joint
302
A steep-sided hill,
composed of sand and gravel,
originating when sediment collected
in openings in stagnant glacial ice
kame
303
A narrow,
terracelike mass of stratified drift
deposited between a glacier and an
adjacent valley wall.
kame terrace
304
A topography consisting of
numerous depressions called
sinkholes.
karst
305
Depressions created
when blocks of ice become lodged
in glacial deposits and subsequently
melt.
kettle holes
306
A massive, concordant
igneous body intruded between
preexisting strata
laccolith
307
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
308
The movement of
water particles in straight-line paths
that are parallel to the channel. The
water particles move downstream
without mixing.
Laminar flow
309
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
310
A red, highly leached soil
type found in the tropics and rich in
oxides of iron and aluminum.
Laterite
311
The northern portion of
Pangaea consisting of North
America and Eurasia.
Laurasia
312
Magma that reaches Earth’s
surface.
Lava
313
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
314
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
315
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
316
The depletion of soluble materials from the upper soil by downward-percolating water.
Leaching
317
Silicate minerals that lack iron and/or magnesium. They are generally lighter in color and have lower specific gravities than dark silicates.
Light silicate
318
The process, generally by cementation and/or compaction, of converting sediments to solid rock.
Lithification
319
The rigid outer layer of Earth, including the crust and upper mantle.
Lithosphere
320
A coherent unit of Earth’s rigid outer layer that includes the crust and upper mantle.
Lithospheric plate
321
See Temporary (local) base level.
Local (temporary) base level
322
Deposits of windblown silt, lacking visible layers, generally buff colored, and capable of maintaining a nearly vertical cliff.
Loess
323
Long ridges of sand oriented parallel to the prevailing wind; these dunes form where sand supplies are limited.
Longitudinal dunes
324
A cross section of a stream channel along its descending course from the head to the mouth.
Longitudinal profile
325
A nearshore current that flows parallel to the shore.
Longshore current
326
Streams that lose water to the groundwater system by outflow through the streambed.
Losing stream
327
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
328
The appearance or quality of light reflected from the surface of a mineral.
Luster
329
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
330
A body of molten rock found at depth, including any dissolved gases and crystals.
Magma
331
A change in Earth’s magnetic field from normal to reverse or vice versa.
Magnetic reversal
332
The detailed history of Earth’s magnetic reversals developed by establishing the magnetic polarity of lava flows of known age.
Magnetic time scale
333
A sensitive instrument used to measure the intensity of Earth’s magnetic field at various points.
Magnetometer
334
The total amount of energy released during an earthquake.
Magnitude (earthquake)
335
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
336
The 2885-kilometer (1789-mile) thick layer of Earth located below the crust.
Mantle
337
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
338
The sum of the number of neutrons and protons in the nucleus of an atom.
Mass number
339
The downslope movement of rock, regolith, and soil under the direct influence of gravity.
Mass wasting
340
An igneous pluton that is not tabular in shape.
Massive
341
A looplike bend in the course of a stream.
Meander
342
A floodplain feature created when an oxbow lake becomes filled with sediment.
Meander scar
343
The physical disintegration of rock, resulting in smaller fragments.
Mechanical weathering
344
A ridge of till formed when lateral moraines from two coalescing valley glaciers join.
Medial moraine
345
The liquid portion of magma excluding the solid crystals.
Melt
346
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
347
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
348
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
349
The changes in mineral composition and texture of a rock subjected to high temperature and pressure within Earth.
Metamorphism
350
A significant change in the chemical composition of a rock, usually by the addition or removal of ions in solution.
Metasomatism
351
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
352
See Oceanic ridge.
Mid-ocean ridge
353
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
354
A naturally occurring, inorganic crystalline material with a unique chemical structure.
Mineral
355
All discovered and undiscovered deposits of a useful mineral that can be extracted now or at some time in the future.
Mineral resource
356
A 12-point scale developed to evaluate earthquake intensity based on the amount of damage to various structures.
Modified Mercalli intensity scale
357
The boundary separating the crust and the mantle, discernible by an increase in seismic velocity.
Mohorovičić discontinuity (Moho)
358
A series of 10 minerals used as a standard in determining hardness.
Mohs scale
359
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
360
A one-limbed flexure in strata. The strata are usually flat-lying or very gently dipping on both sides of the monocline.
Monocline
361
The point downstream where a river empties into another stream or water body.
Mouth
362
A feature in some sedimentary rocks that forms when wet mud dries out, shrinks, and cracks.
Mud crack
363
See Debris flow.
Mudflow
364
The elevated landforms composed of alluvium that parallel some streams and act to confine their waters, except during flood stage.
Natural levees
365
The lowest tidal range, occurring near the times of the first and third quarters of the Moon.
Neap tide
366
The zone of a beach that extends from the low-tide shoreline seaward to where waves break at low tide.
Nearshore zone
367
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
368
As used in climate change, any effect that is opposite of the initial change and tends to offset it.
Negative feedback mechanism
369
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
370
A term for the texture of sedimentary rocks in which the minerals form a pattern of interlocking crystals.
Nonclastic
371
An unconformity in which older metamorphic or intrusive igneous rocks are overlain by younger sedimentary strata.
Nonconformity
372
See Light silicate.
Nonferromagnesian silicate
373
Metamorphic rocks that do not exhibit foliation.
Nonfoliated texture
374
Mineral resource that is not a fuel or processed for the metals it contains.
Nonmetallic mineral resource
375
Resource that forms or accumulates over such long time spans that it must be considered as fixed in total quantity.
Nonrenewable resource
376
A fault in which the rock above the fault plane has moved down relative to the rock below.
Normal fault
377
A magnetic field the same as that which presently exists.
Normal polarity
378
The small, heavy core of an atom that contains all of its positive charge and most of its mass.
Nucleus
379
Incandescent volcanic debris that is buoyed up by hot gases and moves downslope in an avalanche fashion.
Nuée ardente
380
Date that specifies the actual number of years that have passed since an event occurred.
Numerical date
381
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
382
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
383
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
384
The relatively flat submerged zone that extends from the breaker line to the edge of the continental shelf.
Offshore zone
385
A geologic structure that allows for significant amounts of oil and gas to accumulate.
Oil trap
386
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
387
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
388
Layers of sediment are generally deposited in a horizontal or nearly horizontal position.
Original horizontality
389
The processes that collectively result in the formation of mountains.
Orogenesis
390
A layer beneath the mantle about 2270 kilometers (1410 miles) thick that has the properties of a liquid.
Outer core
391
The release of gases dissolved in molten rock.
Outgassing
392
A tongue of ice normally flowing rapidly outward from an ice cap or ice sheet, usually through mountainous terrain to the sea.
Outlet glacier
393
A relatively flat, gently sloping plain consisting of materials deposited by meltwater streams in front of the margin of an ice sheet.
Outwash plain
394
A curved lake produced when a stream cuts off a meander.
Oxbow lake
395
The removal of one or more electrons from an atom or ion. So named because elements commonly combine with oxygen.
Oxidation
396
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
397
The fastest earthquake wave; travels by compression and expansion of the medium.
P wave
398
A lava flow with a smooth-to-ropy surface.
Pahoehoe
399
The study of ancient climates; the study of climate and climate change prior to the period of instrumental records using proxy data.
Paleoclimatology
400
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
401
The systematic study of fossils and the history of life on Earth.
Paleontology
402
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
403
The proposed supercontinent that 200 million years ago began to break apart and form the present landmasses.
Pangaea
404
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
405
Theory that is held with a very high degree of confidence and is comprehensive in scope.
Paradigm
406
A volcanic cone that forms on the flank of a larger volcano.
Parasitic cone
407
The material upon which a soil develops.
Parent material
408
The rock from which a metamorphic rock formed.
Parent rock
409
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
410
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
411
A chain of small lakes in a glacial trough that occupy basins created by glacial erosion.
Pater noster lakes
412
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
413
A texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in diameter.
Pegmatitic texture
414
A localized zone of saturation above the main water table created by an impermeable layer (aquitard).
Perched water table
415
An igneous rock of ultramafic composition thought to be abundant in the upper mantle.
Peridotite
416
A basic unit of the geologic calendar that is a subdivision of an era. Periods may be divided into smaller units called epochs.
Period
417
The tabular arrangement of the elements according to atomic number.
Periodic table
418
Any permanently frozen subsoil. Usually found in the subarctic and arctic regions.
Permafrost
419
A measure of a material’s ability to transmit water.
Permeability
420
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
421
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
422
Conspicuously large crystals in a porphyry that are embedded in a matrix of finer-grained crystals (the groundmass).
Phenocryst
423
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
424
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
425
Basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows.
Pillow lava
426
A vertical conduit through which magmatic materials have passed.
Pipe
427
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
428
A solid celestial body that accumulated during the first stages of planetary formation. Planetesimals aggregated into increasingly larger bodies, ultimately forming the planets.
Planetesimal
429
Permanent deformation that results in a change in size and shape through folding or flowing.
Plastic deformation
430
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
431
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
432
The flat central area of an undrained desert basin.
Playa
433
A temporary lake in a playa.
Playa lake
434
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
435
The process by which pieces of bedrock are lifted out of place by a glacier.
Plucking
436
A structure that results from the emplacement and crystallization of magma beneath Earth’s surface.
Pluton
437
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
438
A crescent-shaped accumulation of sand and gravel deposited on the inside of a meander.
Point bar
439
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
440
The process of linking the same molecules together to form a chain or three-dimensional structure.
Polymerization
441
Two or more minerals having the same chemical composition but different crystalline structures, exemplified by the diamond and graphite forms of carbon.
Polymorphs
442
The volume of open spaces in rock or soil.
Porosity
443
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
444
A texture of metamorphic rocks in which particularly large grains (porphyroblasts) are surrounded by a fine-grained matrix of other minerals.
Porphyroblastic texture
445
An igneous rock with a porphyritic texture.
Porphyry
446
As used in climate change, any effect that acts to reinforce the initial change.
Positive-feedback mechanism
447
A depression formed in a stream channel by the abrasive action of the water’s sediment load.
Pothole
448
All geologic time prior to the Paleozoic era.
Precambrian
449
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
450
Layers of sediment are generally deposited in a horizontal or nearly horizontal position.
Principle of original horizontality
451
The eon following the Archean and preceding the Phanerozoic. It extends between 2.5 billion and 542 million years ago.
Proterozoic eon
452
A positively charged subatomic particle found in the nucleus of an atom.
Proton
453
A developing planetary body that grows by the accumulation of planetesimals.
Protoplanet
454
Data gathered from natural recorders of climate variability such as tree rings, ice
cores, pollen, and ocean-floor
sediments.
Proxy data
455
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
456
The volcanic rock ejected during an eruption. Pyroclastics include ash, bombs, and blocks.
Pyroclastic material
457
An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent eruption.
Pyroclastic texture
458
The removal of loosened blocks from the bed of a channel during times of high flow rates.
Quarrying
459
A system of streams running in all directions away from a central elevated structure, such as a volcano.
Radial drainage pattern
460
The spontaneous decay of certain unstable atomic nuclei.
Radioactivity
461
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)
462
The procedure of calculating the absolute ages of rocks and minerals containing certain radioactive isotopes.
Radiometric dating
463
A dry area on the lee side of a mountain range; many middle-latitude deserts are of this type.
Rainshadow desert
464
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
465
An end moraine formed as the ice front stagnated during glacial retreat.
Recessional moraine
466
A drainage pattern that develops on jointed or fractured bedrock and is characterized by numerous right-angle bends.
Rectangular pattern
467
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
468
Metamorphism associated with large-scale mountain building.
Regional metamorphism
469
The layer of rock and mineral fragments that nearly everywhere covers Earth’s land surface.
Regolith
470
Rocks are placed in their proper sequence or order; only the chronological order of events is determined.
Relative dating
471
A resource that is virtually inexhaustible or that can be replenished over relatively short time spans.
Renewable resource
472
Already identified deposits from which minerals can be extracted profitably.
Reserve
473
The porous, permeable portion of an oil trap that yields oil and gas.
Reservoir rock
474
Soil developed directly from the weathering of the bedrock below.
Residual soil
475
A fault in which the material above the fault plane moves up in relation to the material below.
Reverse fault
476
A magnetic field opposite to that which presently exists.
Reverse polarity
477
A scale of earthquake magnitude based on the motion of a seismograph.
Richter scale
478
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
479
A region of Earth’s crust along which divergence (separation) is taking place.
Rift
480
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
481
Small waves of sand that develop on the surface of a sediment layer by the action of moving water or air.
Ripple marks
482
A general term for a stream that carries a substantial amount of water and has numerous tributaries.
River
483
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
484
A consolidated mixture of minerals.
Rock
485
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
486
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
487
A model that illustrates the origin of the three basic rock types and the interrelatedness of Earth’s materials and processes.
Rock cycle
488
Ground-up rock produced by the grinding effect of a glacier.
Rock flour
489
The rapid slide of a mass of rock downslope along planes of weakness.
Rockslide
490
Water that flows over the land rather than infiltrating into the ground.
Runoff
491
An earthquake wave, slower than a P wave, that travels only in solids.
S wave
492
A white crust on the ground produced when water evaporates and leaves its dissolved materials behind.
Salt flat
493
Transportation of sediment through a series of leaps or bounces.
Saltation
494
A type of foliation characteristic of coarser-grained metamorphic rocks. Such rocks have a parallel arrangement of platy minerals such as the micas.
Schistosity
495
Hardened lava that has retained the vesicles produced by escaping gases.
Scoria
496
See Cinder cone.
Scoria cone
497
An arch formed by wave erosion when caves on opposite sides of a headland unite.
Sea arch
498
An isolated mass of rock standing just offshore, produced by wave erosion of a headland.
Sea stack
499
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
500
An isolated volcanic peak that rises at least 1000 meters (3300 feet) above the deep-ocean floor.
Seamount
