14C method A method for
determining the age in years of organic matter by calculating the amount of
radioactive carbon still remaining, as compared to the stable isotope, 12C.
40K/40Ar method A method used for
the dating of potassium-bearing rocks by using the ratio of radioactive 40K
to its daughter, 40Ar.
aa A Hawaiian term for a lava flow that has
a rough, jagged surface. compare pahoehoe .
ablation As applied to
glacier ice, the process by which ice below the snow line is wasted by
evaporation and melting.
absolute time Geologic time
expressed in years before the present.
abundant metal Iron, aluminum,
magnesium, manganese, and titanium. Ores of the abundant metals only need to be
3 - 5 times as metal-rich as average rock.
abyssal plain Large area of
extremely flat ocean floor lying near a continent and generally over 4 km in
depth.
acceleration The rate at which
velocity changes, either by increasing or decreasing.
accretion The process by
which the terrestrial planets grew, increasing their mass by gradually
accumulating smaller bodies, called planetesimals.
acid mine drainage Water
contamination by sulfuric acid produced by seepage through sulfur-bearing spoil
and tailings from coal and metal mining
acid rain The acidity in
rain due to gases from internal combustion engines and coal- and oil-burning
power plants.
active layer The seasonally
thawed zone above permafrost .
actualism see uniformitarianism .
aftershock An earthquake
that follows and has its epicenter near a larger earthquake.
agate A siliceous rock with alternating
bands of chalcedony and variously colored chert .
alluvial fan Land counterpart
of a delta . An assemblage of sediments marking place
where a stream moves from a steep gradient to a flatter gradient and suddenly
loses transporting power. Typical of arid and semiarid climates but not
confined to them.
alpha decay The process of
radioactive decay in which the nucleus of an atom emits an alpha particle. The
new atom's atomic number is lower by two and its atomic mass number is reduced by four.
alpha particle A particle
consisting of two protons and two neutrons, produced during alpha decay.
Identical to the nucleus of a 4He atom.
alpine glacier see valley glacier .
amygdule A gas cavity (vesicle ) in volcanic rock that has been filled
with mineral matter such as calcite, chalcedony, or quartz.
amygdaloidal A textural term
describing volcanic rocks that contain numerous amygdules.
andesite A fine-grained
volcanic rock of intermediate composition, consisting largely of plagioclase
and one or more mafic minerals.
andesite line The geographic
boundary between rocks of the Pacific Basin, which are basaltic, and those
around the rim of the basin, which are in part andesitic.
angle of incidence The angle at
which a ray of energy approaches a surface.
angle of reflection The angle at
which a reflected ray of energy leaves a surface.
angle of refraction The angle at
which a refracted ray of energy leaves a surface after passing through it.
angle of repose The maximum
angle at which loose material will come to rest when added to a pile of similar
material.
angular unconformity An unconformity in which the beds below the
unconformity dip at a different angle than the beds above it.
anion An ion with a negative electrical charge. That is,
an atom that has gained one or more electrons.
anticline A fold that is
convex upward, or that had such an attitude at some stage of its development. compare
syncline .
aphanitic A textural term
meaning "fine-grained" that applies to igneous rocks.
aquifer A permeable region of rock or
soil through which ground water can move.
aquitard A material of
low permeability that greatly slows the movement of ground water.
arch Forms along a coast as wave
erosion cuts through a headland.
Archean An eon of
geologic time extending from about 3.9 billion years to 2.5 billion years ago.
arête A narrow, saw-toothed mountain
ridge developed by glacier erosion in adjacent cirques .
arkose A sedimentary rock formed by the
cementation of sand-sized grains of feldspar and quartz.
artesian well A well in which
the water in the aquifer is under pressure that raises the water above the
point that the well first encounters it.
assemblage The collection of
minerals that characterize a rock or a facies.
asthenosphere The weak or
"soft" zone in the upper mantle just below the lithosphere , involved in plate movement and
isostatic adjustments. It lies 70 to 100 km below the surface and may extend to
a depth of 400 km. Corresponds to the seismic low-velocity zone .
astronomic theory of glaciation A theory based
on the changing position of the Earth in its orbit around the Sun.
asymmetric rock knob or hill Bedrock forms
with a gentle slope on one side created by glacial abrasion and a steep slope
on the opposite side created by glacial plucking.
atoll A roughly circular reef
with an occasional small, low, coral sand island surrounding a shallow lagoon.
atom A building block of matter, the
smallest particle that has the chemical characteristics of a particular chemical
element. It contains a nucleus of protons and
neutrons surrounded by a cloud of electrons.
atomic mass number The sum of the
number of protons and the number of neutrons in an atom. Approximately equal to
the mass of the atom.
atomic number The number of
protons in an atom, a quantity that determines which element the atom
represents. Example: all atoms of oxygen have 8 protons.
aureole A zone
surrounding an igneous intrusion, in which contact metamorphism has taken place.
authigenesis The process by
which new minerals form in a sediment or sedimentary rock during or after
deposition.
axial plane A geometric plane
that intersects the trough or crest of a fold in such a way that the limbs of
the fold are more or less symmetrically arranged with reference to it.
axis The line formed by the
intersection of the axial plane of a fold with a bedding plane, marking where
the bed shows its maximum curvature.
back-arc basin The region
between an island arc and the continental mainland, commonly
with at least some oceanic crust on its floor.
back swamp A swamp that
forms in the low lying flood plain behind a levee.
backshore Lies between high
tide mark and the foot of the beach dune or the limit of effective wave action.
banded iron formation (BIF) A sedimentary
mineral deposit dominated by iron oxides, carbonates, or silicates that were
deposited chemically from seawater. Most BIFs were formed between 2.5 and 3.5
billion years ago. Their formation is related to the rise of oxygen in the
atmosphere.
bankfull stage A stream
discharge that just fills the stream channel.
bar 1. A mass of sand, gravel, or
alluvium deposited on the bed of a stream, sea, or lake, or at the mouth of a
stream 2. A unit of pressure, approximately equal to atmospheric pressure at
sea level.
barchan A crescent-shaped
sand dune with horns pointing downwind.
barrier beaches or islands Long narrow
beaches separated in many places from the mainland by lagoons.
barrier reef A coral
reef separated from the mainland by a lagoon.
basalt A dark colored extrusive igneous
rock composed chiefly of calcium plagioclase and pyroxene. Extrusive equivalent
of gabbro, underlies the ocean basins and comprises oceanic crust.
base flow Ground water that
enters a stream channel, maintaining stream flow at times when it is not
raining.
base level Of a stream is
the point below which the stream cannot cut. A temporary base level along a stream,
such as a lake may be removed by stream action . Ultimate base level is the
ocean.
basin A synclinal structure, roughly
circular in its outcrop pattern, in which beds dip gently toward the center
from all directions.
batholith A large,
discordant, intrusive body of igneous rock.
bauxite A rock composed
of aluminum hydroxides and impurities in the form of silica, clay, silt, and
iron hydroxides. A residual weathering product, exploited as the primary ore
for aluminum.
bay barrier A beach that cuts
off a bay from the sea.
beach replenishment Rebuilding a
beach by adding sand to it.
beach Temporary accumulations of
sediments that collect between low and high tide marks.
bed load Material in
motion along a stream bed.
bedding A collective term used to signify
presence of beds, or layers, in sedimentary rocks and deposits.
bedding plane Surface
separating layers of sedimentary rocks and deposits. Each bedding plane marks
termination of one deposit and beginning of another of different character, such
as a surface separating a sandstone bed from an overlying mudstone bed. Rock
tends to breaks or separate, readily along bedding planes.
bedrock Any solid rock
exposed at the Earth's surface or overlain by unconsolidated material.
beheaded stream The headwaters
of a stream that have been captured by another stream. compare stream piracy .
berm A small terrace in the backshore
area of the coast with its terrace facing seaward.
beta decay The process of
radioactive decay in which a neutron loses a beta particle, which is physically
identical to an electron. This increases the atomic number of the atom by one by turning the
neutron into a proton. The atom's atomic mass number stays the same because the
total number of protons and neutrons remain the same. The most common form of
radioactive decay.
BIF see banded iron formation
binding energy The energy that
holds the particles in the nucleus of an atom together. It is this energy, when
released, that is used to generate nuclear power.
biogenic sediment Sediments
produced directly by the life processes of plants or animals.
biogenic sedimentary rock A sedimentary
rock composed primarily of biogenic sediments.
bioturbation The turning and
mixing of sediments by organisms.
black smoker A vent on the
seafloor from which hydrothermal fluids are emitted. Upon mixing with seawater
and cooling, the fluids precipitate a cloud of fine-grained sulfide minerals
that resembles a cloud of black smoke.
blind valley A valley in karst that ends abruptly downstream at the point
where its stream disappears underground as a sinking stream.
blowout A an irregular depression excavated
by wind, usually in previously deposited blown sand.
body wave Any seismic wave
that travels through the body of the Earth, rather than along its surface. compare
surface wave.
bond (ionic, covalent, Van der Waals,
metallic) see chemical bond
bottomset bed Layer of fine
sediment deposited in a body of standing water beyond the edge of a growing delta and which is eventually built over by the
advancing delta. Similarly bottomset beds may accumulate in the wind shadow of
a sand dune and be preserved beneath it as the dune advances.
boudinage A structure in
which brittle beds bounded by more ductile ones have been divided into segments
during metamorphism.
boulder train Clusters of erratics from same source, with some
distinctive characteristic that makes their common source easily recognizable.
boundary The tectonic
region in which two plates meet. compare margin.
Bowen's Reaction Series A series of
minerals formed during crystallization of a magma, in which the formation of
minerals alters the composition of the remaining magma. Mafic minerals comprise
a discontinuous series, in which successive minerals form at the expense of
early-formed ones. The plagioclase feldspars form in a continuous series, in
which the composition of plagioclase becomes progressively sodium rich, but the
crystal structure of the mineral does not change.
braided stream A stream with a
complex tangle of converging and diverging channels separated by sand bars or
islands.
branch work cave Cave with
passage ways formed along bedding planes and with an areal pattern similar to
that of surface streams.
breakwater A protective wall
built offshore and usually parallel to the shore.
breccia A clastic rock in
which the gravel-sized particles are angular in shape and make up an
appreciable volume of the rock.
breeder reactor A nuclear reactor
in which 238U or 232Th, which are not easily fissionable, absorb neutrons to
become atoms of 239Pu or 236U, which can later be used as fuels in fission
reactors. Breeder technology is not yet feasible.
brittle Structural
behavior in which a material deforms permanently by fracturing.
brittle limit The stress limit
beyond which a material fractures, rather than behaving in a ductile or elastic
fashion.
burial metamorphism Takes place in an
environment where pressure and temperature are barely more intense than during diagenesis , typically in a deepening sequence of
sediments.
calcarenite A sandstone in which
the sand-sized grains are calcite.
caldera A large, basin-shaped volcanic
depression, more or less circular in form. Typically steep-sided, found at the
summit of a shield volcano .
caliche Gravel, sand, or
desert debris cemented by calcium carbonate, an accumulated product of chemical
weathering in a dry climate. compare claypan, fragipan, hardpan.
calving The breaking away of ice from the
front of the glacier when it ends in a lake or an ocean. Produces icebergs.
cap rock A comparatively
impervious stratum immediately overlying an oil- or gas-bearing rock.
capacity The total amount
of material a stream is able to carry under given conditions.
capillary water Water in the zone of aeration held to soil particles by
surface tension of the water molecules for each other and for the soil
particles.
carbonate conservation depth The water depth
below which the calcium carbonate produced in the ocean is completely
dissolved. There is no calcium carbonate deposition below this level.
carbonate rock A rock
consisting primarily of a carbonate mineral such as calcite or dolomite, the
chief minerals in limestone and dolostone, respectively.
cataclastic metamorphism Takes place in an
environment where intense pressure due to shearing is common, as in a major
fault zone.
cation An ion that has a positive electrical charge. That
is, an atom that has lost one or more electrons.
cave A natural open
space underground, large enough for a person to enter. Most commonly occur by
the dissolution of soluble rocks, generally limestone.
cementation Process by which
a binding, or cementing, agent is precipitated in spaces among individual
particles of a deposit. Common cementing agents are calcite, quartz, and
dolomite.
Cenozoic The current
geologic era, which began 66.4 million years ago and continues to the present.
chain reaction A self-sustaining
nuclear reaction, made possible when neutrons released by fission of some atoms
in a nuclear reactor strike other atoms, causing them to fission as well.
chalcedony A
cryptocrystalline form of quartz, microscopically fibrous with waxy luster. May
be transparent or translucent, and with a uniform tint of white, gray, pale
blue, and, less often, black.
chalk A variety of limestone made up in
part of biochemically derived calcite, in form of skeletons or skeletal
fragments of microscopic oceanic plants and animals mixed with fine-grained
calcite deposits of biochemical or inorganic-chemical origin.
chemical bond The interactions
among the electrons of atoms that hold atoms together to form chemical compounds.
If electrons cluster primarily around one atom of a pair, the bond is ionic .
If they are shared more or less equally, it is covalent . If electrons
move freely between atoms over an extended region, the bond is metallic.
A weak electrostatic bond due to uneven distribution of electrons around atoms
or groups of atoms is a Van der Waals bond.
chemical element A fundamental
substance that cannot be further refined or subdivided by chemical means. All atoms of a chemical element have the same number
of protons.
chemical remanent magnetism Acquired as
magnetic minerals form and align themselves to the global magnetic field during
diagenesis of a sedimentary deposit.
chemical sediment Sediment formed
by chemical precipitation from water. Example: halite precipitated as the
result of the evaporation of sea water.
chemical sedimentary rock A sedimentary
rock made up of chemical sediments. Example: rock salt.
chemical weathering see decomposition
chert A cryptocrystalline form of
quartz, microscopically granular. Occurs as nodules and as thin, continuous
layers. Duller, less waxy luster than chalcedony. Occurs in limestone,
dolostone, and mudstones.
chlorofluorocarbons (CFC) Gases that can be
dissociated by solar radiation, which releases chlorine, which in turn destroys
ozone.
chute cutoff A narrow
"short cut" across a meander bend, formed in flood as the main stream
flow is diverted into a trough between point bars. Sometimes called simply a
'"chute".
cinder cone A conical
volcano formed by the accumulation of pyroclastic debris around a vent.
cirque A steep-walled hollow in a
mountain side, shaped like an amphitheater, or bowl, with one side partially
cut away. Place of origin of a mountain glacier.
clastic Refers to rock or sediments made
up primarily of broken fragments of pre-existing rocks or minerals.
clay 1. The name for a family of
finely-crystalline sheet silicate minerals. 2. Fine-grained soil consisting of
mineral particles, not necessarily clay minerals, that are less than 0.074 mm
in their maximum dimension.
claypan A layer of stiff,
compact, relatively impervious clay which is not cemented. compare caliche , fragipan, hardpan.
cleavage 1. of a
mineral: The tendency of a mineral to split along planes determined by the
crystal structure. 2. of a rock: see slaty cleavage
coal Sedimentary rock composed of
combustible matter derived from the partial decomposition of plant material.
coast A narrow strip of land along the
margin of the ocean extending inland for a variable distance from low water
mark.
col Mountain pass formed by
enlargement of two opposing cirques until their head walls meet and are
broken down.
column Pillar formed as a stalactite
and stalagmite meet.
columnar jointing The type of jointing
that breaks rock, typically basalt, into columnar prisms. Usually the joints
form a more or less distinct hexagonal pattern.
compaction Reduction of pore
space between individual particles as the result of overlying sediments or of
tectonic movements.
competence The maximum size
of particle that a stream can carry.
composite volcano see stratovolcano
Comprehensive Soil Classification System
(CSCS) The classification system in most common use by North American soil
scientists. Categories are based on the chemical and physical characteristics
of a soil. compare USDA Soil Classification System .
compression Squeezing a
material from opposite directions.
concordant Lying parallel
to, rather than cutting across surrounding strata.
concretion A compact
mass of mineral matter, usually spherical or disk-like in shape and embedded in
a host rock of different composition. They form by precipitation of mineral
matter about a nucleus such as a leaf, or a piece of shell of bone.
conduction Heat transport by
direct transfer of energy from one particle to another, without moving the
particle to a new location. compare convection , radiation .
cone of depression A downward
distortion or dimple in the water table that forms as a well pumps water faster
than it can flow through the aquifer.
conglomerate A clastic
sedimentary rock composed of lithified beds of rounded gravel mixed with sand.
Constancy of Interfacial Angles The statement
that the angles between congruent crystal faces on samples of a single mineral
are always identical. A consequence of, and therefore evidence for the
existence of crystalline structure in minerals.
contact metamorphism Metamorphism
genetically related to the intrusion (or extrusion) of magmas and taking place
in rocks at or near their contact with a body of igneous rock.
continental arc A belt of
volcanic mountains on the continental mainland that lie above a subduction
zone. compare island arc .
continental crust The part
of the crust that directly underlies the continents and continental shelves.
Averages about 35 km in thickness, but may be over 70 km thick under largest
mountain ranges.
continental deserts Located in
continental interior far from moisture-bearing winds.
continental divide A major drainage divide separating the drainage to one
ocean from another.
continental drift The theory that
explained the relative positions and shapes of continents, the formation of
mountains, and other large-scale geologic phenomena as results of the lateral
movement of continents. The crust of ocean basins was assumed to be relatively
immobile. compare plate tectonics , sea floor spreading .
continental ice glacier An ice sheet that
obscures all but the highest peaks of a large part of a continent.
continental rise The portion of
the continental margin that lies between the abyssal plain and the continental
slope. The continental rise is underlain by crustal rocks of the ocean
basin.
continental shelf The portion of
the continental margin that extends as a gently sloping surface from the
shoreline seaward to a marked change in slope at the top of the continental
slope . Seaward depth averages about 130 m.
continental slope That part of the
continental margin that lies between the continental shelf and the continental
rise. Slope relatively steep, 3o - 6o. The continental slope is underlain
by crustal rocks of the continent.
convection Heat transport by
moving particles, and the thermal energy that they carry, to a new location. compare
conduction , radiation .
convection cell A cyclical
pattern of movement in a fluid body such as the ocean, the atmosphere, or the
Earth's mantle, driven by density variations which in turn are the result of
differences in temperature from one part of the fluid to another.
convergent boundary A boundary
between two plates of the Earth's crust that are pushing together.
co-product A mineral
commodity that is recovered from a mining operation for some other mineral
product. Example: Platinum is commonly a co-product of nickel mining.
coquina A coarse-grained, porous variety of
clastic limestone made up chiefly of shells and shell fragments.
core Innermost zone of Earth. Consists
of two parts, an outer liquid section and an inner solid section, both chiefly
of iron and nickel with about 10 percent lighter elements. It is surrounded by
the mantle.
correlation Process of
establishing contemporaneity of rocks or events in one area with rocks or
events in another area.
crater 1. A steep-walled, usually conical
depression at the summit or on the flanks of a volcano, resulting from the
explosive ejection of material from a vent. 2. A bowl-shaped depression
with a raised, overturned rim produced by the impact of a meteorite or other
energetic projectile.
craton The stable portions of the
continents that have escaped orogenic activity for the last 2 billion years.
Made predominantly of granite and metamorphic rocks. compare orogen .
creep 1. The very slow, generally
continuous downslope movement of soil and debris under the influence of
gravity. 2. The movement of sand grains along the land surface.
crevasse 1. Breach in a
natural levee . 2. Deep crevice or open fracture in
glacier ice.
cross-bedding see inclined bedding .
cross-cutting relationships Geologic
discontinuities that suggest relative ages: A geologic feature is younger than the
feature it cuts. Thus, a fault cutting across a rock is younger than the rock.
crust The upper part of the lithosphere , divided into oceanic crust and continental crust .
crystal The multi-sided
form of a mineral, bounded by planar growth surfaces, that is the outward
expression of the ordered arrangement of atoms within it.
crystal settling Gravitational
sinking of crystals from the liquid in which they formed, by virtue of their
greater density. A type of igneous differentiation.
crystal structure The regular and
repeated three-dimensional arrangement of atoms or ions in a crystal.
crystalline 1. Having a
crystal structure. 2. When referring to sedimentary rocks, crystalline
designates a texture in which mineral crystals have formed in an interlocking
pattern. see nonclastic. 3. As a generic term, geologists use the
term "crystalline rocks" as a rough synonym for "igneous or
metamorphic rocks".
cumulate An igneous rock
that forms by crystal settling .
Curie point The temperature
above which a mineral loses its magnetism.
current ripple mark An asymmetric
ripple mark formed by wind or water moving generally in one direction. Steep
face of ripple faces in direction of current. compare oscillation ripple mark .
cyclothem A series of beds,
of interest because they include coal, which were associated with unstable
shelf or interior basin conditions in which alternating marine transgressions
and regressions occurred.
Darcy's law A formula
describing the flow of water through an aquifer.
daughter An atom that
results from the radioactive decay of a parent atom.
debris flow Fast-moving,
turbulent mass movement with a high content of both water and rock debris. The
more rapid debris flows rival the speed of rock slides.
decay rate The rate at
which a population of radioactive atoms decays into stable daughter atoms. Rate
often expressed in terms of half life of the parent isotope .
decomposition (chemical weathering) Weathering
processes that are the result of chemical reactions. Example: the
transformation of orthoclase to kaolinite.
deflation A process of erosion
in which wind carries off particles of dust and sand.
dehydration Any process by
which water bound within a solid material is released. Example: Gypsum
(CaSO4·2H2O) becomes anhydrite (CaSO4) by dehydration.
delta An assemblage of sediments
accumulated where a stream flows into a body of standing water and its velocity
and transporting power are suddenly reduced. . A "delta plain" is the
upper surface of a delta.
dendritic drainage A stream pattern
that, when viewed on a map or from the air, resembles the branching pattern of
a deciduous tree such as a maple or oak.
denudation The sum of the
processes that result in the wearing away or the progressive lowering of the
Earth's surface by weathering, erosion, mass wasting, and transportation.
depositional environment The nature of
the environment in which sediments are laid down. They are immensely varied and
may range from the deep ocean to the coral reef and the glacial lake of the
high mountains. The nature of the depositional environment may be deduced from
the nature of the sediments and rock deposited there.
depositional remanent magnetism Develops as
magnetic minerals settle through water and align themselves in the Earth's
magnetic field.
desert pavement A lag
accumulation of pebbles or boulders that cuts off further deflation .
desertification A process of
land degradation initiated by human activity, particularly in the zones along
the margins of deserts.
detrital sedimentary rock A sedimentary
rock made up of detrital sediments.
detrital sediments Sediments made
of fragments or mineral grains weathered from pre-existing rocks.
diagenesis All the physical,
chemical, and biologic changes undergone by sediments from the time of their
initial deposition, through their conversion to solid rock, and subsequently to
the brink of metamorphism.
differential weathering Weathering that
occurs at different rates, as the result of variations in composition and
mechanical resistance of rocks, or differences in the intensity of weathering
processes.
differentiation The process of
developing more than one rock type, in situ, from a common magma.
dike A tabular igneous intrusion that
cuts across the surrounding rock.
dilatancy An increase in
the bulk volume of rock during deformation. Possibly related to the migration
of water into microfractures or pores.
dip The angle that a structural
surface such as a bedding plane or fault surface makes with the horizontal,
measured perpendicular to the strike and in the vertical plane.
dip pole see magnetic
pole
dip slip fault A fault on which
the movement is parallel to the dip of the fault plane.
directed pressure Pressure applied
predominately in one direction, rather than uniformly.
discharge In a stream, the
volume of water passing through a channel in a given time.
disconformity An unconformity in which the beds above the
unconformity are parallel to the beds below the unconformity.
discordant Cutting across
surrounding strata.
disintegration (mechanical weathering) The processes of
weathering by which physical actions such as frost wedging break down a rock
into fragments, involving no chemical change.
dissolution A chemical
reaction in which a solid material is dispersed as ions in a liquid. Example:
Halite (NaCl) undergoes dissolution when placed in water.
dissolved load Amount of
material water carries in solution.
distributary channels Stream channels
that fan out from the upstream point of the delta and carry the
sediments that build the delta.
divergent boundary Boundary between
two crustal plates that are pulling apart.
dolostone A carbonate rock
made up predominately of the mineral dolomite, CaMg(C03)2.
dome An uplift or anticlinal structure,
roughly circular in its outcrop exposure, in which beds dip gently away from
the center in all directions.
drag fold A minor fold
produced within a weak bed or adjacent to a fault by the movement of surrounding
rocks in opposite directions.
drainage basin The area
from which a stream and its tributaries receives its water.
drainage divide The line
that separates one drainage basin from another.
drift Glacial deposits laid down
directly by glaciers or laid down in lakes, ocean, or streams as result of
glacial activity.
dripstone Calcium
carbonate deposited from solution as water enters a cave through the zone of
aeration. Forms stalactites, stalagmites and other cave deposits.
drumlin Streamlined hill,
largely of till, with blunt end pointing into direction from
which ice moved. Occur in clusters called drumlin fields.
dry farming Farming without
irrigation in drylands.
drylands A general term
for semiarid and desert lands.
ductile Structural
behavior in which a material deforms permanently without fracturing.
dust bowl An area subject
to dust storms, especially south central United States.
dust devil A small,
dust-bearing whirlwind.
dust storm Large volume of
dust-sized particles lifted high into the atmosphere.
Earth system System involving
continuous interaction of the solid Earth, the atmosphere, the oceans and
living things.
earthflow A form of slow, but
perceptible, mass movement, with high content of water and rock debris. Lateral
boundaries are well-defined and the terminus is lobed. With increasing moisture
content grades into a mudflow.
eccentricity of the Earth's orbit A measure of the
circularity of the Earth's orbit. It varies in cycles of about 100,000 and
400,000 years.
elastic Non-permanent
structural deformation during which the amount of deformation (strain) is
proportional to the stress.
elastic rebound The statement
that movement along a fault is the result of an abrupt release of a
progressively increasing elastic strain between the rocks on either side of the
fault.
elasticity The tendency for
a body to return to its original shape and size when a stress is removed.
electron A fundamental
unit of matter, negatively charged and disposed in a cloud surrounding the
nucleus of an atom.
electron capture Nuclear decay in
which a proton in the nucleus acquires an electron from the outer cloud of the
atom's electrons. This converts the proton to a neutron, reduces the number of
protons in the nucleus by one and atomic number of the original element by one.
Atomic mass number remains constant because the total
number of protons and neutrons is unchanged.
electron shell A characteristic
energy level with which an electron is associated. Electrons occupy discrete
shells within the cloud surrounding an atom's nucleus. These may be thought of,
loosely, as if they represented orbits at distinct heights above the nucleus.
element see chemical element
end moraine see terminal
moraine.
eon The primary division of geologic
time which are, from oldest to youngest, the Hadean, Archean, Proterozoic, and
Phanerozoic eons.
epicenter The point on the
Earth's surface that is directly above the focus of an earthquake.
epoch A division of geologic time next
shorter than a period. Example: the Pleistocene epoch is in the
Quaternary period.
equilibrium line On a glacier the
line separating the zone of accumulation from the zone of ablation .
era A division of geologic time next
smaller than the eon and larger than a period. Example: The
Paleozoic era is in the Phanerozoic eon and includes, among others, the
Devonian period.
erratic A stone or boulder, glacially
transported from place of origin and left in an area of different bedrock
composition.
esker A winding ridge of stratified drift . Forms in a glacial tunnel and, when ice melts,
stands as ridge up to 15 m high and kilometers in length.
ETP curve see Milankovitch curve .
eustatic change in sea level A worldwide
change in sea level, such as caused by melting glaciers.
eutrophication The process of
aging of lakes by the addition of nutrients.
evaporite A mineral or
rock deposited directly from a solution (commonly seawater) during evaporation.
For example, gypsum and halite are evaporite minerals.
exfoliation The process by
which concentric scales, plates, or shells of rock are stripped or spall from
the bare surface of a large rock mass.
exfoliation dome A large
dome-shaped form that develops in homogeneous crystalline rocks as the result
of exfoliation.
exotic river A river that is
able to maintain its flow through a desert because of water received from
outside the desert.
extrusive Pertaining to
igneous rocks or features formed from lava released on the Earth's surface.
facies see metamorphic facies , sedimentary facies
failed rift A rift emanating from a plate triple junction along which minimal
divergence has taken place.
fall When applied to mass movement of
material refers to free fall of material moving without contact with the
surface.
fault The surface of rock rupture along
which there has been differential movement of the rock on either side.
fault gouge Soft, uncemented,
pulverized clay-like material found along some faults.
ferromagnesian Containing iron
and magnesium, applied to the mafic minerals. Example: olivine.
fetch Distance over which wave-forming
winds blow.
field capacity see specific
retention.
fiery cloud see nuée ardente .
fjord Glaciated valleys now flooded by
the sea.
firn (névé) Granular ice
formed by the recrystallization of snow. Intermediate between snow and glacier
ice.
fission The spontaneous
or induced splitting, by particle collision, of a heavy atomic nucleus into a
pair of fragments plus some neutrons. Controlled induced fission can be used as
a source of nuclear power.
fission track dating Dating of minerals
by fission tracks, damage tracks left in a mineral by spontaneous alpha
emissions.
fissure eruption An eruption of
lava that takes place from a fracture, usually without producing a cone.
flash flood A flood that
rises and falls very rapidly.
flashy stream A stream with a
high, short flood peak and short lag time.
flint A variety of chert , often black because of included organic
matter.
flood Peak flow that tops the banks of
a stream channel.
flood recurrence interval The number of
years of record plus 1 divided by the rank of each maximum annual flood.
floodplain Area bordering a
stream over which water spreads when the stream tops its channel banks.
flow When applied to mass movement,
refers to a chaotic movement of material in continuous contact with the ground
surface, commonly involving a moderate to high amount of water.
flow folding A fold formed in
relatively fluid rocks that have flowed toward a synclinal trough.
flowstone General
term for deposits formed by dripping and flowing water on walls and floors of
caves.
fluid inclusion A tiny cavity in
a crystal, commonly 1 to 100 microns in diameter, containing liquid and/or gas.
Formed by the entrapment of fluid during the growth or subsequent deformation
of the crystal.
focus The point within the Earth which
is the center of an earthquake, at which strain energy is first released and
converted to elastic wave energy.
foliation A planar
structure that develops in metamorphic rocks as a result of directed pressure .
fold and thrust mountains Mountains,
characterized by extensive folding and thrust faulting, that form at convergent
plate boundaries on continents.
foot wall block The body of rock
that lies below an inclined fault plane. compare hanging wall block
formation water The water, held
in pore volume in sedimentary rocks, that has persisted with little change in
composition since it was buried with the sediment.
foreset bed Inclined layers
of sediment deposited on the advancing margin of a growing delta or along the
slip face of a sand dune.
foreshock A minor tremor
that precedes an earthquake. An increase in seismicity may signal that a major
release of strain energy is about to occur.
foreshore Lies between low
and high tide marks.
fossil Evidence in rock of the presence
of past life, such as a dinosaur bone, an ancient clam shell, or the footprint
of a long-extinct animal.
fossil fuel A hydrocarbon
(coal or petroleum) that can be extracted from the Earth for use as a fuel.
Fossil fuels are non-renewable energy sources.
fractional crystallization A sequence of
crystallization from magma in which the early-formed crystals are prevented
from reacting with the remaining magma, resulting in a magma with an evolving
chemical composition.
fragipan A dense layer of
soil, containing silt and sand but no organic matter and little clay, whose
extreme hardness and impermeability are due primarily to compaction. compare
caliche , claypan, hardpan.
free oscillation A vibration of a
body such as a bell or the Earth that continues without further influence after
an initial event.
fringing reef A coral
reef attached directly to the mainland.
frost wedging A type of disintegration in which jointed rock is forced
apart by the expansion of water as it freezes in fractures.
fusion The combination of two light
nuclei to form a heavier nucleus, with the accompanying release of energy. This
is the source of energy in a hydrogen bomb. If it could be controlled, it could
serve as an alternative to fission in nuclear power generation.
gabbro A coarse-grained igneous rock, chemically
equivalent to a basalt .
gardening The constant and
slow churning of the lunar regolith as the result of meteorite impacts.
geanticline An anticlinal
structure presumed to form in the context of geosynclinal evolution. Not in
current use since the development of plate tectonic theory.
geode Roughly spherical, hollow or
partially hollow accumulation of mineral matter. A few centimeters to nearly
0.5 m in diameter. Outer layer of chalcedony lined with crystals that
project toward the hollow center. Crystals, often perfectly formed, usually
quartz although calcite and dolomite and - more rarely - other minerals. Most
commonly occur in limestone, and less often in shale.
geologic column The arrangement
of rock units in the proper chronological order from youngest to oldest.
geologic time scale The
chronological sequence of units of Earth time.
geophysics
As the name implies, geophysics involves
the application of physical theories and
measurements
to discover the properties of the earth. The disciplines dates to antiquity,
mainly
as a
scientific approach to earthquake prediction (A problem still unsolved), but
major progress
began
in the late 1500's with initial work in such areas as magnetism and gravity.
Tremendous
improvements
in instrumentation in the early years of the20th century generated rapid
progress
in
geophysics and ultimately led, in the 1960's, to the theory of plate tectonics.
Plate tectonics,
the study of the interior structure of the earth, and such related areas as
global
and
regional processes are known collectively as solid earth geophysics. The
subdiscipline
known
as exploration geophysics involves the use of geophysical theory and
instrumentation to
locate
petroleum and other mineral sources. Unlike solid earth geophysics, exploration
geophysics
generally concentrates on finding lateral heterogeneities in a relatively small
part of
the
earth's crust.
Geophysics has
increased dramatically man's ability to exploit natural resources. Human
senses
cannot quantify, or even detect (e.g., magnetism) many physical phenomena.
Humans
cannot
detect variations in he earth's gravitation field of one part per million, but
modern gravity
meters
can (in fact, to 0.02 parts per million or better). Seismology, the primary
method of
petroleum
exploration, requires exact timing and recording of very low-amplitude
vibrators,
vibrations
(or shaking) that is far below that which a human would sense.
The following
definitions are from Robert E. Sheriff's "Encyclopedic Dictionary of
Exploration
Geophysics".
geophysics:
1.The
study of the earth by quantitative physical method, especially by seismic
reflection
and refraction, gravity, magnetic, electrical, electromagnetic, and
radioactivity methods.
2.The application of physical principles to studies of the earth. Includes the
branches of (a)
seismology (earthquakes and elastic waves); (b) geothermometry (heating of the
earth,
heat flow, volcanology, and hot springs); (c) hydrology (ground and surface
water,
sometimes including glaciology); (d) physical oceanography; (e) meteorology;
(f) gravity
and geodesy (the earth's gravitational field and the size and form of the
earth); (g)
atmospheric electricity and terrestrial magnetism (including ionosphere, Van
Allen belts,
telluric currents, etc.); (h) tectonophysics (geological processes in the
earth); and (i)
exploration and engineering geophysics. Geochronology (the dating of earth
history) and
geocosmogony (the origin of the earth) are sometimes added to the foregoing
list.
3.Often refers to solid-earth geophysics only, thus excluding (c), (d), (e),
and portions of
other subjects from the above list.
4.Exploration geophysics is the use of seismic, gravity, magnetic, electrical,
electromagnetic, etc., methods in the search for oil, gas, minerals, water,
etc., with the
objective of economic exploitation.
geophysicist
1.One who
studies the physical properties of the earth or applies physical measurements
to
geologic problems; a specialist in geophysics.
geosyncline A downwarping of
the Earth's crust, either elongate or basin-like, measured in scores of
kilometers, in which sedimentary and volcanic rocks accumulate to thicknesses
of thousands of meters. Not in current use since the development of plate
tectonic theory.
geothermal energy Heat extracted
from the Earth for use as an power source.
geothermal gradient The rate at
which temperature increases with depth below the surface.
geyser A type of thermal spring which ejects
water intermittently with considerable force.
glaciation The formation,
advance and retreat of glaciers and the results of these activities.
glacier A mass of ice, formed by the
recrystallization of snow, that flows forward, or has flowed at some time in
the past.
glacier ice Ice with
interlocking crystals that makes up the bulk of a glacier.
glass An inorganic solid in which there
is no crystalline structure .
glassy A texture of extrusive igneous
rocks that develops as the result of rapid cooling, so that crystallization is
inhibited.
global warming The prediction
that climate will warm as a result of the addition to the atmosphere of humanly
produced greenhouse gases.
gneiss A coarse, foliated metamorphic
rock in which bands of granular minerals (commonly quartz and feldspars)
alternate with bands of flaky or elongate minerals (e.g., micas, pyroxenes).
Generally less than 50% of the minerals are aligned in a parallel orientation.
gneissosity The style of
foliation typical of gneiss.
Gondwana The southern
portion of the late Paleozoic supercontinent known as Pangea. It means,
literally "Land of the Gonds" (a people of the Indian subcontinent).
The variant Gondwanaland found in some books, therefore, is a tautology.
gouge see fault gouge
graben see rift
graded bedding Type of bedding sedimentary
deposits in which individual beds become finer from bottom to top.
gradient Slope of a stream
bed or hillside. The vertical distance of descent over horizontal distance of
slope.
granite Light colored, coarse grained,
intrusive igneous rock characterized by the minerals orthoclase and quartz with
lesser amounts of plagioclase feldspar and iron-magnesium minerals. Underlies
large sections of the continents.
granitic belt A region of
granitic rock, one of two characteristic regions within cratons .
granitization A metamorphic
process by which solid rock is converted into granite by the addition or
removal of material, without passing through a magmatic stage. compare metasomatism .
gravitational heating Planetary heating
caused by the conversion of potential energy into heat. Associated with the iron
catastrophe .
gravitational moisture Water in the zone
of aeration that is moving down toward the zone of saturation.
graywacke (lithic
sandstone) A variety of sandstone characterized by angular-shaped grains of
quartz and feldspar, and small fragments of dark rock all set in a matrix of
finer particles.
greenhouse gases Gases (primarily
water and carbon dioxide, but also a variety of sulfur and nitrogen compounds
and gaseous hydrocarbons) that trap the Sun's heat in the atmosphere.
greenstone An altered or
metamorphosed mafic igneous rock that owes its dark color to the presence of
chlorite, epidote, or amphiboles.
greenstone belt A region of
greenstones, one of two characteristic regions within cratons .
groin A wall built out from the shore,
usually at perpendicular to it to trap sand carried by longshore currents .
groove A broad, deep, generally straight
furrow carved in bed rock by the abrasive action of debris embedded in a moving
glacier. Larger and deeper than a glacial striation.
ground moraine Till deposited
from main body of glacier during ablation.
ground water table see water table .
ground water Water beneath
the Earth's surface.
guyot see seamount
habit A general term for the outward
appearance of a mineral, defined by the relative sizes and arrangement of
characteristic crystal faces.
Hadean The oldest eon in Earth history,
extending from the origin of the Earth to about 3.9 billion years ago.
half-life The amount of
time that it takes for one half of an original population of atoms of a
radioactive isotope to decay.
hanging valley A valley whose
mouth is high above the floor of the main valley to which it is tributary.
Usually, but not always, the result of mountain glaciation.
hanging wall block The body of rock
that lies above an inclined fault plane. compare foot wall block
hardness Resistance of a
mineral to scratching, determined on a comparative basis by the Mohs scale .
hardpan A general term
for a relatively hard layer of soil at or just below the ground surface,
cemented by silica, iron oxide, calcium carbonate, or organic matter. compare
caliche , claypan, fragipan.
head (hydraulic head) The level
to which ground water in the zone of saturation will rise.
heat flow The amount of
thermal energy leaving the Earth per cm2/sec.
heave In mass movement the upward
motion of material by expansion as, for example, the heaving caused by freezing
water.
hiatus A gap or interruption in the
continuity of the geologic record either because the record was never formed or
because it was destroyed by erosion. It represents the time interval spanned by
an unconformity .
high level nuclear waste Radioactive
waste from defense activities of the U. S. government and from spent fuel rods
from nuclear reactors.
hinge fault A fault along
which there is increasing offset or separation along the strike of the fault
plane, from an initial point of no separation.
hoodoo A column or pillar of rock
produced by differential weathering in a region of sporadic heavy
rainfall, commonly facilitated by joints and by rock layers of varying
hardness.
Hooke's Law A statement of
elastic deformation, that strain is directly proportional to stress.
horn The sharp spire of rock formed as
glaciers in several cirques erode into a central mountain peak.
horst compare rift
hot spot A region of high heat flow on the Earth's surface, thought to lie
above a mantle plume .
humus The generally dark, more or less
stable part of the organic matter in a soil, so well decomposed that the
original sources cannot be identified.
hydraulic conductivity Measure of permeability
in Earth materials.
hydraulic gradient The slope of the
water table. Measured by the difference in elevation between two points
on the slope of the water table and the distance of flow between them.
hydraulic head see head.
hydrograph Graph of
variation of stream flow over time.
hydrologic system (or hydrologic cycle) The pattern of
water circulation from the ocean to the atmosphere to the land and back to the
ocean.
hydrolysis A decomposition
reaction involving water, in which hydrogen ions (H+) or hydroxyl ions (OH-)
replace other ions. The result is a new residual mineral. Example: the addition
of water to orthoclase produces kaolinite and releases K+ and silica into
solution.
ice sheet A broad,
mound-like mass of glacier ice that usually spreads radially outward from a
central zone.
ice shelf A floating ice
sheet extending across water from a land-based glacier.
icecap A small ice sheet.
igneous rock A rock that has
crystallized from a molten state.
inclined bedding (cross-bedding) Bedding laid down
at an angle to the horizontal, as in many sand dunes.
inclined fold A fold whose
axial plane is inclined from the vertical, but in which the steeper of the two
limbs is not overturned. compare overturned fold.
inclusion (xenolith)
A fragment of older rock caught up in an igneous rock.
index fossil A fossil that
identifies and dates the strata in which it is typically found. To be most useful,
an index fossil must have broad, even worldwide distribution and must be
restricted to a narrow stratigraphic range.
index mineral A mineral formed
under a particular set of temperature and pressure conditions, thus characterizing
a particular degree of metamorphism.
inertia The tendency of a
body to resist acceleration . A moving body tends to keep moving at a
constant speed in the same direction, and a stationary body tends to remain in
one place, unless acted upon by an outside force.
inner core The solid
innermost part of the core with a diameter of a little over 1,200 km.
intensity A measure of the
size of an earthquake in terms of the damage it causes.
interlobate moraine Ridge formed
along junction of adjacent glacier lobes.
intrusive Pertaining to
igneous rocks or features formed by the emplacement of magma in pre-existing
rock.
ion An atom that has an electrical
charge, by virtue of having gained or lost electrons. see cation,
anion
ionic radius The effective
distance from the center of an ion to the edge of its electron cloud.
ionic substitution The replacement
of one or more ions in a crystal structure by others of similar size and
electrical charge. Example: Fe2+ is interchangeable with Mg2+ in most
ferromagnesian minerals.
iron catastrophe The period in the
Hadean eon during which much of the iron in outer portions of the Earth
migrated toward the center of the planet, producing the core and releasing
large amounts of gravitational heat.
ironpan A hardpan in
which iron oxides are the primary cementing agents.
island arc A curved belt of
volcanic islands lying above a subduction zone. compare continental
arc.
isochemical reaction A reaction in
which chemical constituents of a rock are rearranged to form a new mineral
assemblage, but no material is added to or lost from the rock as a whole.
Applied generally to diagenetic or metamorphic environments.
isoclinal fold A fold in which
the limbs are parallel.
isograd A line on a map
joining points at which metamorphism took place under similar temperature and
pressure conditions, as indicated by rocks belonging to the same metamorphic facies . Generally, the line
separates two adjacent metamorphic zones, as indicated by specific .
isotope Atoms that differ in atomic mass number , but not in atomic number , are called isotopes. For example,
oxygen (atomic number 8) may have an atomic mass number of 16, 17, or 18,
depending on whether it has 8, 9, or 10 neutrons. It therefore has three
isotopes.
isoseismal line A line on a map
joining points of equal earthquake intensity.
isostasy The condition of
equilibrium, comparable to floating, of units of the lithosphere above the asthenosphere .
isostatic change in sea level A sea level
change due to change in load on Earth's crust.
jasper A red variety of chert , its color coming from minute particles of
included hematite.
jet flow Flow in which
fluid moves at high speed in jet-like surges as does water in free fall over a
falls.
jetty Similar to a groin but
built to keep sand out of a harbor entrance.
joint A surface of fracture in a rock,
without displacement parallel to the fracture.
juvenile hydrothermal fluid A hot fluid,
largely water, presumed to have been released from a magma.
kame Stratified drift deposited in depressions and cavities in
stagnant ice and left as irregular, steep sided hills when the ice is melts.
kame terrace Stratified drift deposited between wasting glacier and
adjacent valley wall. Stands as a terrace when glacier melts.
karst A landscape that develops
from the action of ground water in areas of easily soluble rocks. Characterized
by caves, underground drainage and sinkholes.
kettle Depression in ground surface
formed by the melting of a block of glacier ice buried or partially buried by drift .
komatiite An ultramafic
rock with a non-cumulate texture, presumed to be extrusive.
laccolith A concordant
igneous intrusion with a flat floor and a convex upper surface, usually less than
8 km across and from a few meters to a few hundred meters thick at its thickest
point.
lag time The delay in the
response of stream flow between precipitation and flood peak.
lahar A mudflow composed chiefly
of pyroclastic material on the flanks of a volcano.
laminar flow Fluid flow in
which flow lines are distinct, and parallel and do not mix. compare turbulent
flow .
lateral continuity The extent of a
rock unit over a considerable but definite area.
lateral moraine Moraine formed
by valley glaciers along valley sides.
laterite A highly
weathered red soil rich in iron and aluminum oxides. Typically formed in a
tropical to temperate climate where intense chemical weathering is common.
Laurasia The northern
portion of the late Paleozoic supercontinent called Pangea.
lava Molten rock that
flows at the Earth's surface.
lava dome A steep-sided
rounded extrusion of highly viscous lava squeezed out from a volcano and
forming a dome-shaped or bulbous mass above and around the volcanic vent. The
structure generally develops inside a volcanic crater.
lava flood (plateau basalt) A term applied to
large areas of basaltic lava presumably extruded from fissures.
lava lake A lake of lava,
usually basaltic, in a volcanic caldera.
layered complex An intrusive
igneous body in which there are layers of varying mineral content.
levees Banks of sand and silt along
stream bank built by deposition in small increments during successive floods.
limb The portions of a fold that are
away from the hinge; the "sides" of the fold.
limestone A sedimentary
rock composed mostly of the mineral calcite, CaCO3.
linear dune Long, straight
dune with slip faces on each side.
lineation A general term applying
to any linear feature in a metamorphic rock.
liquefaction The
transformation of a soil from a solid to a liquid state as the result of
increased pore pressure.
lithic sandstone see graywacke.
lithification The process by
which an unconsolidated deposit of sediments is converted in to solid rock.
Compaction, cementation and recrystallization are involved.
lithophile Said of an
element that has a greater chemical affinity for silicate rocks than for
sulfides or for a metallic state. Example: Aluminum.
lithosphere The rigid
outer shell of the Earth. It includes the crust and uppermost mantle and is on
the order of 100 km in thickness.
lithostatic stress The confining
(non-directed) pressure imposed by the weight of overlying rock.
littoral current see longshore current .
load Of a stream, the amount that it
carries at any one time.
loess Deposits of wind-borne dust.
longshore current (littoral
current) A current that flows parallel to the shore just inside the surf
zone. Also called the littoral current.
longshore drift The general
movement of sediment parallel to the shoreline. Waves generally carry sediment
up the shore face at an angle to the shoreline, but carry it straight out
again, resulting in a net longshore displacement.
Love wave A seismic surface
wave that has a horizontal (side-to-side) component but no vertical
component.
low level nuclear waste (TRU) Comes
largely from national defense utilities and includes contaminated lab coasts,
gloves, and laboratory equipment.
low velocity zone The seismic
region within the upper mantle that corresponds to the asthenosphere .
luster The manner in which light reflects
from the surface of a mineral, described by its quality and intensity.
mafic Referring to a generally
dark-colored igneous rock with significant amounts of one or more ferromagnesian minerals, or to a magma with
significant amounts of iron and magnesium.
magma Molten rock, containing dissolved
gases and suspended solid particles. At the Earth's surface, magma is known as lava .
magma ocean A global-scale
ocean of magma, according to some calculations several hundred kilometers deep,
thought to have existed during the final stages of accretion as the
Earth was forming.
magnetic anomaly The amount by
which a measurement of the local magnetic field intensity exceeds or falls
below the intensity of the global magnetic field.
magnetic chron Time during which
magnetic polarity is dominantly normal or dominantly reversed.
magnetic declination Angle of
divergence between true north and magnetic north. Measured in degrees east or
west of true, or geographic north.
magnetic equator Lies half way
between the north and south magnetic poles.
magnetic inclination The angle of dip
of the compass needle as it varies from horizontal at the magnetic equator to
vertical at the magnetic poles.
magnetic polarity The direction,
north (normal) or south (reversed), that a magnetic compass needle points.
magnetic polarity time scale A chronology
based on the shifting polarity of the Earth's magnetic field.
magnetic pole The point on the
Earth's surface where a magnetic needle points vertically downward (north
magnetic pole) or vertically upward (south magnetic pole).
magnetic stratigraphy A stratigraphic
sequence based on the magnetic polarity of the rocks.
magnetic subchron A period during
a magnetic chron when the magnetic polarity is the opposite from that of the
magnetic chron.
magnetic polarity The direction,
north (normal) or south (reversed) that a magnetic needle points.
magnitude A measure of the
strength of an earthquake based on the amount of movement recorded by a seismograph . compare Richter scale.
mantle That portion of the Earth
below the crust and reaching to about 2,780 km, where a transition zone of
about 100 km thickness separates it from the core.
mantle plume A hypothetical
column of hot, partially molten material that rises from an indeterminate depth
in the mantle and is thought by some geologists to provide a driving force for
plate movement. compare hot spot .
marble A metamorphic rock composed
largely of calcite. The metamorphic equivalent of limestone.
margin The tectonic region that lies at
the edge of a continent, whether it coincides with a plate boundary or not.
mass movement The downslope
movement of material under the influence of gravity.
maze cave Caves in which
passageways have interconnecting loops that form a maze-like pattern.
meander A sharp bend, loop or turn in a
stream's course. When abandoned, called a meander scar or an oxbow .
medial moraine Formed by the
merging of lateral moraines as two valley glaciers join.
mélange (clastic wedge) A mappable body
of rock characterized by blocks and fragments of all sizes, embedded in a
sheared matrix. A tectonic mélange commonly forms in the upper portions of a
subduction zone, where crustal rock is crushed and sheared.
mesosphere A zone in the
Earth between 400 and 670 km below the surface separating the upper mantle from
the lower mantle.
Mesozoic An era of time during
the Phanerozoic eon lasting from 245 million years ago to 66.4 million ago.
metal porphyry deposit A mineral
deposit genetically related to a pluton of porphyritic rock, commonly
granodiorite. Scarce metals are typically enriched by the passage of
hydrothermal fluids through rocks surrounding the intrusion, with the result
that a metal-rich halo forms there.
metamorphic facies A set of
metamorphic mineral assemblages, repeatedly associated in space and time, such
that there is a constant and therefore predictable relationship between mineral
composition and chemical composition. That relationship is a consequence of
conditions of temperature and pressure under which the assemblages are stable.
metamorphic rock A rock changed
from its original form and/or composition by heat, pressure, or chemically
active fluids, or some combination of them.
metamorphic zone A mappable
region in which rocks have been metamorphosed to the same degree, as evidenced
by the similarity of mineral assemblages in them.
metamorphism The processes of
recrystallization, textural and mineralogical change that take place in the
solid state under conditions beyond those normally encountered during
diagenesis.
metasomatism The metamorphic
processes that occur as a result of the passage of chemically active fluids
through a rock, adding to or removing constituents during metamorphism.
microplate see terrane
migmatite A composite rock
composed of igneous and metamorphic materials, the result of partial melting at
the upper limit of metamorphism.
Milankovitch curve (ETP curve )
A graph representing the amount of solar radiation received at the Earth's
surface at a particular latitude and time and based on the variations in the
Earth's orbital motions.
mineral A naturally occurring
inorganic solid that has a well-defined chemical composition and in which atoms
are arranged in an ordered fashion.
mineral deposit Any natural
concentration of a valuable material in the Earth's crust, whether that
material can be extracted profitably or not.
Modified Mercalli Scale A commonly used
scale of earthquake intensity.
Mohorovicic discontinuity (Moho) The sharp seismic
velocity discontinuity that separates the crust and the mantle.
Mohs scale The ten-point
scale of mineral hardness , keyed arbitrarily to the minerals
talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum,
and diamond.
molecule The smallest unit
of matter that has the chemical and physical properties of a particular
chemical compound.
momentum transfer In a rock slide
the forward transfer of energy by the collision of one block of rock with the
next block forward. The process makes possible progressively more rapid
movement of material in downslope positions.
monocline A simple fold,
described as a local steepening in strata with an otherwise uniform dip.
moraine Landform made largely of till.
mountain glacier see valley glacier .
mud cracks Cracks,
generally polygonal, caused by the shrinking of a deposit of clay or silt under
surface conditions.
mudflow Form of mass movement similar to
a debris flow but containing less rock material.
mudstone A fine-grained
detrital sedimentary rock made up of clay- and silt-sized particles.
mylonite A chert-like rock
without cleavage but with a banded or streaky structure produced by extreme
shearing of rocks that have been pulverized and rolled during intense dynamic
metamorphism.
nappe A sheet of rock that has moved
over a large horizontal distance by thrust faulting, recumbent folding, or
both, so that it lies on rocks of markedly different age or lithologic
character.
neck cutoff Occurs as a
river cuts through the narrow neck of a meander. Sometimes called simply a
"cutoff."
neutron A particle in the nucleus of an atom,
which is without electrical charge and with approximately the same mass as a
proton.
névé see firn.
nivation Erosion beneath
and around edges of a snow bank. Results can foreshadow a cirque.
nodule A small, irregular,
knobby-surfaced rock body that differs in composition from the rock that
encloses it. Formed by the replacement of the original mineral matter. Quartz
in the form of flint or chert is the most common component. Most common in
limestone and dolostone.
nonclastic A term applied
to sedimentary rocks that are not composed of fragments of pre-existing rocks
or minerals. The term "crystalline" is more commonly used.
nonconformity An unconformity that separates profoundly different
rock types, such as sedimentary rocks from metamorphic rocks.
normal fault A dip-slip fault on which the hanging wall block is offset downward relative to
the foot wall block . compare reverse fault .
normal polarity Time when the
compass needle points to the magnetic north pole.
north magnetic pole The point on the
Earth where the north-seeking end of a magnetic needle, free to swing in space,
points directly down.
nuclear power Power generated
by controlled fission or (potentially) fusion reactions, the heat
from which is used to produce steam and drive turbines.
nucleus (atomic) The center of an
atom, containing both protons and (except for 1H) neutrons.
nuée ardente (fiery cloud) A dense, hot
(sometimes incandescent) cloud of volcanic ash and gas produced in a Pelean
eruption.
oblique-slip fault A fault with both
dip-slip and strike-slip components of movement.
obliquity of the Earth's ecliptic Tilt of the
Earth's rotational axis in relation to the plane in which the Earth circles to
Sun. Cycles from about 21.5o through 24.5o and back to 21.5o every 41,000
years.
oceanic crust That part of the
crust underlying the ocean basins. Composed of basalt and having a thickness of
about 5 km.
oil shale A mudrock that
will yield liquid or gaseous hydrocarbons upon distillation.
oolite Spheroidal grains of sand size,
usually composed of calcite and thought to have formed by inorganic
precipitation.
open pit mining Surficial mining,
in which the valuable rock is exposed by removal of overlying rock or soil.
ophiolite A suite of mafic and
ultramafic rocks and associated marine cherts and their metamorphic
equivalents.
ore The naturally occurring material
from which a mineral or minerals of economic value can be extracted at a
profit.
ore deposit A continuous
well-defined mass of material of sufficient ore content to make
extraction economically feasible. compare mineral deposit .
original horizontality Refers to the
condition of beds or strata as being horizontal or nearly horizontal when first
formed.
orogen Linear to arcuate in plan,
intensely deformed crustal belt associated with mountain building. compare
craton .
orogeny The process of mountain building.
oscillation ripple mark A symmetric
ripple mark formed by waves, which move water back and forth. compare current ripple mark .
outer core The outermost
part of the core. It is liquid, about 1,700 km thick, and separated from the inner,
solid core by a transition zone about 565 km thick.
outwash Beds of sand and gravel laid down
by glacial melt water
outwash plain A plain
underlain by outwash.
overbank deposits Sediments
deposited from flood water on the flood plain.
overturned fold An inclined fold
in which one limb has been tilted beyond the vertical, so that the
stratigraphic sequence within it is reversed. compare inclined fold.
oxbow An abandoned meander .
oxbow lake A lake in an
abandoned meander.
oxidation The decomposition process by which iron or other
metallic elements in a rock combine with oxygen to form residual oxide minerals.
ozone hole Decrease of
ozone in the stratosphere.
P- wave (primary wave, compressional
wave) A seismic body wave that involves particle motion,
alternating compression and expansion, in the direction of wave propagation. It
is the fastest seismic wave. compare S-wave .
pahoehoe A Hawaiian term
for a basaltic lava flow with a smooth, or ropy surface. compare aa .
paleomagnetism Study of the
Earth's past magnetism as it is recorded in the rocks.
paleosol A buried soil
horizon of the geologic past.
Paleozoic An era of
geologic time lasting from 570 to 245 million years ago.
Pangea A supercontinent that existed from
about 300 to 200 million years ago, and included most of the continental crust
of the Earth.
parabolic dune A sand dune that
is parabolic in plan with slip face convex downwind.
parent A radioactive element whose decay
produces stable daughter elements.
partial melting The igneous
process in which a rock begins to melt at the lower end of its melting
interval, yielding a magma with a chemical composition different from the bulk
composition of the parent rock.
pascal A unit of pressure, equal to
1/100,000 of a bar .
pedalfer A generic term
used to describe the soils typically formed in a humid region.
Characteristically have an accumulation of iron and aluminum oxides and
hydroxides.
pedocal A generic term
used to describe the soils typically found in an arid or semiarid region.
Characteristically have an accumulation of carbonates, particularly calcite.
pegmatite An extremely
coarse-grained igneous rock with interlocking crystals, usually with a bulk
chemical composition similar to granite but commonly containing rare minerals
enriched in lithium, boron, fluorine, niobium, and other scarce metals.
Pegmatites are also the source for many gem-quality precious and semiprecious
stones.
pegmatitic Having the
texture of a pegmatite.
pelagic ooze A deep ocean
sediment consisting of at least 30% skeletal remains of calcareous or siliceous
microorganisms, the rest being clay minerals.
Peléan eruption A type of
volcanic eruption characterized by nuées ardentes and the development of lava domes .
peneplain Low gently,
rolling landscapes produced by long-continued erosion.
perched water table A water table
that develops at a higher elevation than the main water table. <peridotite
An ultramafic igneous rock, the major constituent of the mantle.
periglacial Refers to
conditions in a near glacial climate.
period In the geologic time scale a unit
of time less than an era and greater than an epoch. Example: The
Tertiary period was the earliest period in the Cenozoic era and included, among
others, the Eocene epoch.
permafrost table The depth in a
permafrost region at which the maximum temperature reaches 0o C.
permafrost Soil conditions
prevailing in area whose mean annual temperature is 0o C.
permeability The capacity of
material to transmit water or other fluids.
petroleum A general term
including both oil and natural gas.
phaneritic A textural term
meaning "coarse-grained" that applies to igneous rocks.
Phanerozoic the most recent
eon of geologic time beginning 570 million years ago and continuing to the
present.
phenocryst Any relatively
large, conspicuous crystal in a porphyritic igneous rock. compare porphyroblast.
phyllite A metamorphosed
mudstone with a silky sheen, more coarse-grained than a slate and less
coarse-grained than a schist.
piedmont glacier A glacier that spreads
out at the foot of mountains, formed by the coalescence of two or more valley
glaciers.
pillow A structure observed in certain
igneous rocks extruded into water, characterized by discontinuous,
close-fitting, pillow-shaped masses, commonly 30 to 60 cm across.
pipe A vertical conduit through the
Earth's crust below a volcano, through which magma has passed.
pirate stream A stream that
captures the headwaters of another stream.
placer A surficial mineral deposit formed
by mechanical concentration of valuable minerals from weathered debris, usually
through the action of stream currents or of waves.
plate A rigid segment of the Earth's
lithosphere that moves horizontally and adjoins other plates along zones of
seismic activity. Plates may include portions of both continents and ocean
basins.
plate boundaries The zones of
seismic activity long which plates are in contact. These may coincide with
continental margins , but usually do not. Movement between plates is
predominately horizontal, and may be divergent, or convergent, or side-by-side.
plate tectonics A theory
of global tectonics according to which the lithosphere is divided into mobile plates.
The entire lithosphere is in motion, not simply those segments composed of
continental material. compare continental drift
plate triple junction A point from
which three rifts emanate at roughly 120 degree angles.
Example: the Afar triangle in East Africa.
playa A broad flat desert basin, often
containing an ephemeral playa lake.
plucking (quarrying)
A process of erosion in which the glacier pulls loose pieces of bed rock.
plume The movement of water along flow
lines from a point source of ground water pollution toward its eventual
emergence at the surface.
plunging fold A fold in which
the axis is inclined at an angle from the horizontal.
pluton An igneous intrusion.
pluvial lake A lake formed
during a pluvial period.
pluvial period Time when a
dryland area had greater effective moisture than at present.
pocket beach Small, narrow
beach, usually crescentic, at head of a bay or small inlet.
point bar Accumulations of
sand and gravel deposited in slack water on inside of a winding or meandering
river.
polar deserts Deserts in which
most moisture is locked up in ground ice and unavailable as liquid water.
polar glacier A glacier whose
temperature throughout is always below freezing.
polish A smooth, polished surface
imparted to some rock types by glacier abrasion.
polymetamorphism A series of
events in which two or more metamorphic episodes have left their imprint on the
same rocks.
polymorphism The circumstance
in which two minerals with different crystalline structures have identical
chemical compositions. Example: Diamond and graphite.
porosity The percentage of
material occupied by pore space.
porphyritic A texture of an
igneous rock in which large crystals (phenocrysts) are set in a matrix of
relatively finer-grained crystals or of glass.
porphyroblast A large crystal
of a mineral such as garnet or staurolite set in a matrix of much finer-grained
minerals in a metamorphic rock. compare phenocryst.
potentiometric surface The level to
which water will rise in an artesian system when its confining aquitard is
pierced.
pothole A hole or basin cut into bedrock
of a stream by the abrasive action of pebbles and sand swirled by turbulent
stream flow.
Precambrian An informal term
to include all geologic time from the beginning of the Earth to the beginning
of the Cambrian period 570 million years ago.
precession of the equinox The wobble of
the Earth as it spins changes the direction in which its axis of rotation
points. One wobble takes about 23,000 years.
pressure melting The phenomenon
causing increased melting of ice by increase of pressure.
Principle of faunal and floral succession Groups of
animals and plants have succeeded one another in a definite and discernible
order.
prograde A succession of
metamorphic conditions, each of which is at a higher temperature and/or
pressure than the preceding one.
Proterozoic The geologic eon
lying between the Archean and Phanerozoic eons, beginning about 2.5 billion
years ago and ending about 0.57 billion years ago.
proton A fundamental particle of matter.
Provides a positive charge in the nucleus of an atom.
pyroclastic Pertaining to
clastic material formed by volcanic explosion or aerial expulsion from a
volcanic vent.
quarrying 1. The process
by which building stone, usually in blocks or sheets, is extracted from the
Earth.. 2. see plucking
quartz arenite A sandstone in
which the sand grains are predominantly quartz.
quartzite A metamorphic
rock consisting largely of interlocking quartz grains; the metamorphic
equivalent of a sandstone or chert.
radial drainage A pattern in
which streams radiate outward from a high central zone.
radiation Heat transport
without the intervention of matter, as in the transport of heat from the Sun to
the Earth. compare conduction , convection .
radioactivity The spontaneous
decay of the nucleus of an element. It involves the change in the number of
protons in the nucleus and therefore creates an atom of a new element.
radiocarbon 14C derived from
14N as cosmic ray bombardment adds a neutron to its nucleus and the nucleus
emits a proton. Radiocarbon decays back to 14N by beta decay . Half life
is 5730 ± 30 years.
rain shadow deserts Deserts formed by
blocking moisture-bearing winds with mountain barriers.
ramp The planar surface sloping
seaward from the foot of the shore face.
rapids Turbulent stream water flow down
a steep gradient, but not as steep as in a waterfall.
Rayleigh wave A type of seismic
surface wave in which particles follow a backward elliptical orbit in a
vertical plane.
reaction rim A peripheral zone
around a mineral grain, composed of another mineral.
recessional moraine Ridges of
glacial till marking halt and slight readvance of glacier during its
general retreat.
rectangular drainage A pattern in
which a stream and its tributaries follow courses marked by nearly right angle
bends.
recumbent fold A fold in which
the axial plane is horizontal.
refraction 1. Bending
of waves or rays of energy, e.g. seismic waves. 2. As applies to the near shore
environment, the bending of wave crests as they approach the shore.
regional metamorphism Metamorphism
affecting an extensive region, associated with orogeny .
regolith A layer of
unconsolidated fragmental rock material.
rejuvenation Renewed stream
erosion, generally as the result of uplift. Generates features of youthful
topography on a landscape that was previously worn down to a base level.
relative time Dating of rocks
and geologic events by their positions in chronological order without reference
to number of years before the present.
remanent magnetism Magnetism
acquired by a rock as some time in the past.
reserves That portion of
the resources for a valuable mineral commodity that can be extracted
from the Earth at a profit today.
reservoir rock Any porous and
permeable rock that yields oil or natural gas.
residual (resistant) mineral A mineral that
persists in soil after weathering, either because it was resistant to
weathering or because it was formed during the weathering process.
residual soil A soil presumed
to have developed in place as the product of decomposition and disintegration
of bedrock .
resources The reserves
of a valuable mineral commodity plus all other mineral deposits that may
eventually become available, even those that are presumed to exist but have not
yet been discovered and those that are not economically or technologically
exploitable at the moment. The total mineral endowment ultimately available for
extraction.
retrograde A succession of
metamorphic conditions, each one of which is at a lower temperature and/or
pressure than the preceding one.
reverse fault A dip-slip fault on which the hanging wall block is offset upward relative to
the foot wall block . compare normal fault .
reversed polarity Time when a
magnetic needle points to the south pole.
rhyolite A fine-grained
silica-rich igneous rock, the extrusive equivalent of granite.
Richter scale A commonly used
measure of earthquake magnitude , based on a logarithmic scale. Each integral
step on the scale represents a tenfold increase in the extent of ground
shaking, as recorded on a seismograph.
rift (graben) A valley caused
by extension of the Earth's crust. Its floor forms as a portion of the crust
moves downward along normal faults .
rip current Carries excess
water in the longshore current out through the surf zone where
it dissipates.
ripple marks of oscillation
Symmetrical ripple marks formed by oscillating movement of water such as may be
found along the coast just outside the surf zone.
ripple marks Small
waves produced by wind or water moving across deposits of sand or silt.
rock An aggregate of one or more
minerals in varying proportions.
rock avalanche see rockslide.
rock cleavage see cleavage
rock cycle The concept of a
sequence of events involving the formation, alteration, destruction and
reformation of rocks as a result of geologic processes and which is recurrent,
returning to a starting point. It represents a closed system. compare rock
system.
rock flour Finely divided
rock material ground by glacial action and fed by streams fed by melting
glaciers.
rock glacier A mass of
ice-cemented rock rubble found on slopes of some high mountains. Movement is
slow, averaging 30 to 40 cm/yr.
rock record The history
recorded in rocks.
rockslide (rock avalanche) A slide involving
a downward and usually sudden movement of newly detached segments of bedrock
sliding or slipping over an inclined surface of weakness such as a bedding
plane, fault plane, or joint surface.
rock system The concept of a
sequence of events involving the formation, alteration, destruction and reformation
of rocks as a result of geologic processes. Unlike the rock cycle it is an open
system and does not return to a starting point. compare rock cycle
rock varnish A thin, shiny
veneer of clay minerals and iron and manganese oxides deposited on some rocks
in a desert environment.
rock waste Angular
fragments of rock. Forms a talus if abundant enough.
rockfall The sudden fall
of one or more large pieces of a rock from a cliff.
roundness The degree to
which a sedimentary particle's corners and edges are rounded.
runoff The precipitation that runs
directly off the surface to stream or body of standing water.
S wave (secondary wave , shear wave) A seismic body wave that involves particle motion from side
to side, perpendicular to the direction of wave propagation. S-waves are slower
than P-waves and cannot travel through a liquid. compare P-wave .
salinization. A process by
which salts accumulate in soil
salt-water invasion Displacement of
fresh surface or ground water by the advance of salt water.
saltation A process of
sediment transport in which a particle jumps from one point to another.
sand dune An accumulation
of wind driven sand into a distinctive shape.
sand sea A large area
completely, or nearly completely, covered with sand dunes.
sandstone A clastic
sedimentary rock in which the particles are dominantly of sand size, from 0.062
mm to 2 mm in diameter.
sandstorm A blanket of
wind-driven sand with an upper surface about a meter above ground level.
sanitary land fill An artificial
hill formed by the refuse of present-day civilization.
schist A strongly foliated, coarsely
crystalline metamorphic rock, produced during regional metamorphism, that can
readily be split into slabs or flakes because more than 50% of its mineral
grains are parallel to each other.
schistosity The foliation in
a schist, due largely to the parallel orientation of micas.
seafloor spreading Process by
which ocean floors spread laterally from crests of main ocean ridges. As
material moves laterally from the ridge, new material replaces it along the
ridge crest by welling upward from the mantle. compare continental drift , plate tectonics
seamount (guyot) A volcanic
mountain on the seafloor. If flat-topped, it is a guyot.
seawall A wall at the
shore and parallel to it for protection against wave erosion
sedimentary facies An accumulation
of deposits that exhibits specific characteristics and grades laterally into
other sedimentary accumulations that were formed at the same time but exhibit
different characteristics.
sedimentary rock Rock formed from
the accumulation of sediment, which may consist of fragments and mineral grains
of varying sizes from pre-existing rocks, remains or products of animals and
plants, the products of chemical action, or mixtures of these.
seismic gap A segment of an
active fault zone that has not experienced a major earthquake during a time
period when most other segments of the zone have. Generally regarded as having
a higher potential for future earthquakes.
seismic sea wave (tsunami) A sea wave
produced by any large-scale, short duration disturbance on the seafloor,
commonly a shallow submarine earthquake but possibly also a submarine slide or
volcanic eruption.
seismic tomography A technique for
three-dimensional imaging of the Earth's interior by using a computer to
compare the seismic records from a large number of stations. Similar in concept
to a CAT scan used for medical purposes.
seismograph An instrument
that detects, magnifies, and records vibrations of the Earth, especially
earthquakes.
seismology The study of
earthquakes, and of the structure of the Earth by both natural and artificially
generated seismic waves.
seismoscope An instrument
that merely indicates the occurrence of an earthquake.
self-exciting dynamo In reference to
the Earth, the suggestion that movements in the fluid core may help initiate
the Earth's magnetic field.
shadow zone A region 100º to
140º from the epicenter of an earthquake in which, due to refraction from below
the core-mantle boundary, no direct seismic waves can be detected.
shale A mudstone that splits or
fractures readily.
shatter cone A distinctively
striated conical structure in rock, ranging from a few centimeters to a few
meters in length, believed to have been formed by the passage of a shock wave
following meteorite impact.
shear Rock deformation involving
movement past each other of adjacent parts of the rock and parallel to the
plane separating them.
shear strength The resistance
of a body to shear stress.
shear stress The stress on an
object operating parallel to the slope on which it lies.
sheeting A type of
jointing produced by pressure release (unloading) or exfoliation .
shield volcano A volcano in the
shape of a flattened cone, broad and low, built by very fluid flows of basaltic
lava.
shock lamellae Closely spaced
microscopic planes, distinct from cleavage planes, that occur in shock-metamorphosed
minerals and are regarded as important indicators of shock metamorphism.
shock metamorphism Metamorphism
induced in rock by the passage of a high-pressure shock wave acting over a
period of time from a few microseconds to a fraction of a minute. The only
known natural cause of shock metamorphism is the hypervelocity impact of a
meteorite.
shore Seaward edge of coast between low
tide and effective wave action.
shore face The concave
section of the beach from high tide mark down to the ramp between 5 and 20 m
off shore.
shore platform A surface of
erosion that slopes gently seaward from a cliff base to the low tide mark.
shoreline The line
separating land and water. Fluctuates as water rises and falls.
sial The upper layer of the continental
crust, so called because it is rich in silica and aluminum oxide. compare sima.
sialic Enriched in sial.
silica Silicon dioxide (SiO2) as a pure
crystalline substance makes up quartz and related forms such as flint
and chalcedony . More generally, silica is the basic chemical
constituent common to all silicate minerals and magmas.
silica tetrahedron The basic
structural unit of which all silicates are composed, consisting of a silicon
atom surrounded symmetrically by four oxygen atoms. The structure, therefore,
has the form of a tetrahedron with an oxygen atom at each corner.
sill A tabular igneous intrusion that
parallels the planar structure of the surrounding rock.
sima The oceanic crust, also the lower
layer of the continental crust, so called because it is enriched in silica and
magnesium oxide. compare sial.
sinkhole Depression in
ground surface caused by collapse into a cave below.
sinking stream A stream that
empties into the underground into a cave, usually through a sinkhole.
slate A compact, fine-grained
metamorphic rock that has slaty cleavage.
slaty cleavage A style of
foliation common in metamorphosed mudstones, characterized by nearly
flat, sheet-like planes of breakage, similar in appearance to a deck of playing
cards. compare cleavage
slickenside A polished and
smoothly striated surface that results from friction along a fault plane.
slide A mass movement in which material
maintains continuous contact with the surface on which it moves.
slip face Steep face on
lee side of sand dune.
slump Downward and outward rotational
movement of Earth materials traveling as a unit or series of units.
smelting The process of
removing metal from ore.
snow line The elevation at
which snow persists throughout the year.
snowfields Expanses of snow
that lie above the snow line.
soil All unconsolidated materials above
bedrock. Natural earthy materials on the Earth's surface, in places
modified or even made by human activity, containing living matter, and
supporting or capable of supporting plants out of doors.
soil horizon A layer of soil
that is distinguishable from adjacent layers by characteristic physical
properties such as texture, structure, or color, or by chemical composition.
soil moisture Ground water in
the zone of aeration
soil structure The combination
of soil particles into aggregates or clusters which are separated from adjacent
aggregates by surfaces of weakness.
soil texture The physical
nature of the soil, according to its relative proportions of sand, clay, and
silt.
sole mark Develops as an
irregularity on the bottom of a stratum. It is a cast of a depression on the
top surface of the immediately underlying bed.
solifluction Turbulent
movement of saturated soil or surficial debris.
sorting The range of
particle sizes in a sedimentary deposit. A deposit with a narrow range of
particle sizes is termed "well-sorted."
south magnetic pole The point on the
Earth where a north seeking magnetic needle free to swing in space points
directly up.
specific gravity The ratio of the
density of a material to the density of water.
specific retention (field
capacity) The amount of capillary water retained in a soil after the
drainage of gravitational moisture.
sphericity A descriptive
term to describe how close a particle's shape is to a sphere.
spit A sandy bar built out from the
land into a body of water.
spoil Overburden or non-ore removed in
mining or quarrying.
spreading axis (spreading center) A region of
divergence on the Earth's surface, as at a rift .
spreading pole A rotational pole
around which a plate appears to rotate on the Earth's surface.
spring Occurs at the intersection of the
water table with the ground surface.
stack An isolated, steep-sided, rocky
mass or island just offshore from a rocky headland, usually on a shore
platform.
stalactite An
icicle-shaped accumulation of dripstone hanging from cave roof.
stalagmite A post of dripstone growing up from a cave floor.
star dune A sand dune
built by winds alternating through several directions. Builds vertically rather
than migrating and growing laterally.
stick-slip A jerky, sliding
motion associated with fault movement.
stock A small batholith.
stoping A process of
magmatic intrusion that involves detaching and engulfing pieces of the
surrounding rock, so that the magma moves slowly upward.
storm surge A ridge of high
water associated with a hurricane and which floods over the shore .
strain Change in the shape or volume of a
body as a result of stress.
strain rate The rate at which
a body changes shape or volume as a result of stress.
strain seismograph A seismograph that is designed to detect deformation
of the ground by measuring relative displacement of two points.
stratification The accumulation
of material in layers or beds.
stratified drift Debris washed
from a glacier and laid down in well-defined layers.
stratigraphy The succession
and age relation of layered rocks.
stratovolcano (composite
volcano) A volcano that is composed of alternating layers of lava and
pyroclastic material, along with abundant dikes and sills. Viscous,
intermediate lava may flow from a central vent. Example: Mt. Fuji in Japan.
streak The color of a mineral in its
powdered form, usually obtained by rubbing the mineral against an unglazed
porcelain tile to see the mark it makes. A mineral harder than the tile must be
pulverized by crushing.
stream capture see stream piracy.
stream order A classification
of the relative hierarchy of stream segments in a drainage network.
stream piracy (stream
capture) The natural diversion of the headwaters of one stream into
the channel of another stream that has greater erosional activity and flows at
a lower level.
stream terrace A relatively
flat surface along a valley, with a steep bank separating it either from the
floodplain, or from a lower terrace.
strength The ability to
withstand a stress without permanent deformation.
stress The force per unit area acting on
any surface within a solid; also, by extension, the external pressure which
generates the internal force.
striations Scratches, or
small channels, gouged by glacier action. Occur on boulders, pebbles, and
bedrock. Striations along bedrock indicate direction of ice movement.
strike The compass direction of the
intersection between a structural surface (e.g., a bedding plane or a fault
surface) and the horizontal.
strike-slip fault (transcurrent fault) A fault on which
the movement is parallel to the fault's strike.
strip mining Open pit mining,
typically for coal.
subduction zone A narrow,
elongate region in which one lithospheric plate descends relative to another.
sublimation The process by
which matter in the solid state passes directly to the gaseous state without
first becoming liquid.
subtropical deserts Deserts in zones
of descending air between 25 degrees and 30 degrees north and south latitude.
superimposed stream A stream that
was established on a new surface and then, as it cut downward, maintained its
course despite encountering different lithologies in the process.
superposition A statement of
relative age in layered rocks: In a series of sedimentary rocks that has not
been overturned, the topmost layer is always the youngest and the bottommost
layer is always the oldest.
surf Produced as a wave steepens and
falls forward as the wave nears the shore.
surface of discontinuity In sand dune
formation the surface between quiet air of the wind shadow and the rapidly
moving air above.
surface wave compare body wave
surging glacier A glacier that
moves rapidly (tens of meters per day) as it breaks away from the ground
surface on which it rests.
suspended load The amount of
material a stream carries in suspension.
suspension A method of
sediment transport in which the turbulence of a fluid is able to keep particles
supported in the fluid.
suture The line of juncture where
continental rocks on two converging plates meet. Example: The region in the
Himalayas where the Eurasian and Indian-Australian plates meet.
swash and back wash Uprush of a wave
onto the beach followed by the return flow of the water down the beach slope in
the intervals between waves.
swells Persistence of wind-formed waves
after wind ceases.
syncline A fold that is
convex downward, or that had such an attitude at some stage in its development.
compare anticline.
taconite A bedded
ferruginous chert containing at least 25% iron. A potential iron ore.
tailings Washed or milled
ore that is too poor to be further treated.
talus A slope built up by the
accumulation of rock waste at the foot of a cliff or ridge.
tar A thick brown to black viscous
organic liquid, too thick to migrate easily through most porous sediment.
tar sand A sand containing
tar or asphalt, from which the hydrocarbons may potentially be extracted by
distillation.
tarn A lake in the bedrock basin of a cirque.
tell An artificial hill formed by the
debris of successive human settlements.
temperate glacier A glacier whose
temperature throughout is at, or close to, the pressure point of ice, except in
winter when it is frozen for a few meters below the surface.
tensile fracture A fracture caused
by tensional stress in a rock.
tension A stress that tends to pull a
body apart.
tephra A general term for all pyroclastic material.
terminal moraine (end moraine)
Ridge of till marking farthest extent of glacier.
terrane (microplate) A fragment of the
lithosphere, smaller than a plate, that forms a portion of an accreted terrane margin
.
texture The general appearance of a rock
as shown by the size, shape, and arrangement of the materials composing it.
"The present is the key to the
past" A shorthand reference to the principle of uniformitarianism .
thermal conductivity A measure of the
ability of a material to conduct heat.
thermal gradient see geothermal
gradient.
thermal spring A spring whose
temperature is 6.5o C or more above mean annual air temperature.
thermoremanent magnetism The magnetism of
a mineral that it is acquired as it cools below its Curie point.
threshold of movement The point at
which a slope or slope material crosses from a condition of stability to one of
instability and movement begins.
thrust fault A reverse fault on which the dip angle of the fault
plane is 15 degrees or less.
thrust sheet A body of rock
above a large-scale thrust fault.
tidal delta A delta
formed at both sides of a tidal inlet.
tidal inlet Waterway from
open ocean into a lagoon.
tidal power Power generated
by harnessing the energy of tidal motion in the ocean.
till (unstratified drift)
Glacial drift composed of rock fragments that range from
clay to boulder size and randomly arranged without bedding.
topset bed Layer of
sediments deposited over surface of a delta, nearly horizontal and covering the
tops of the inclined foreset beds.
triangulation The method of
locating an epicenter by determining how far it lies from three widely
separated seismographs.
transcurrent fault see strike-slip fault
transform boundary A plate boundary
in which plates on opposite sides of the boundary move past each other in
opposite directions.
transform fault A plate boundary
that ideally shows pure strike-slip movement. Associated with the offset
segments of midocean ridges.
transported soil A soil that has
been moved from the site of its parent rock.
transverse dune A long, straight
dune, perpendicular to direction of wind.
trap 1. Any barrier to the upward
migration of petroleum, allowing it to accumulate. 2. Any dark colored
extrusive igneous rock. A reference to the tendency of basalt and similar rocks
to form columnar joints.
travel - time diagram A plot of
seismic wave travel time against distance on the Earth's surface from the
epicenter of an earthquake.
travertine (tufa) Variety
of limestone which forms stalactites and stalagmites and other
deposits in limestone caves (dripstone) and the mouths of hot and cold
calcareous springs.
trellis drainage A drainage
pattern in which a stream and its tributaries resemble the pattern of a vine on
a trellis.
trench Along, narrow, steep-walled, often
arcuate depression in the ocean floor, much deeper than the adjacent ocean and
associated with a subduction zone .
troughs and bars Linear features
in unconsolidated sediments at the foot of the shoreface, the result of
breaking waves.
TRU see Low level nuclear
waste.
truncated spur The
beveled end of a ridge separating two valleys where they join a larger
glaciated valley. Glacier of main valley has eroded back the end of the ridge.
tufa see travertine .
tuff A general term for all
consolidated pyroclastic rock. Not to be confused with tufa.
turbidite Sedimentary
deposit settled out of turbid water carrying particles of widely varying grade
size. Characteristically displays graded bedding.
turbulent flow Fluid flow in
which the flow lines are confused and mixed. Fluid moves in eddies and swirls. compare
laminar flow.
U-shaped valley A valley carved
by glacier erosion and whose cross-valley profile has steep sides and a nearly
flat floor, suggestive of a large letter "U".
unconformity A buried erosion
surface separating two rock masses.
uniformitarianism The principle
that applies to geology our assumption that the laws of nature are constant As originally
used it meant that the processes operating to change the Earth in the present
also operated in the past and at the same rate and intensity and produced
changes similar to those we see today. The meaning has evolved and today the
principle of uniformitarianism acknowledges that past processes, even if the
same as today, may have operated at different rates and with different
intensities than those of the present. The term "actualism" is
sometimes used to designate this later meaning.
unloading The release of
confining pressure associated with the removal of overlying material. May
result in expansion of rock, accompanied by the development of joints or sheeting
.
unstratified drift see
till
USDA Soil Classification System A classification
of soils on the basis of the processes and conditions by which they form. compare
Comprehensive Soil Classification System.
valley glacier( alpine
glacier, mountain glacier ) Streams of ice that flow down
valleys in mountainous areas.
valley train Outwash plain
contained within valley walls.
varve A pair sedimentary units, one
coarse-grained, the other fine-grained, interpreted as representing one year of
sedimentation.
velocity Distance of
travel in unit of time
velocity profile A plot of seismic
velocity against depth in the Earth.
ventifact A pebble, cobble,
or boulder faceted by wind driven sand.
vesicle A cavity in a
lava, formed by the entrapment of a gas bubble during solidification of the
lava.
vesicular A textural term
applied to an igneous rock containing abundant vesicles, formed by the
expansion of gases initially dissolved in the lava.
viscosity The internal
resistance to flow in a liquid.
volcanic ash The dust-sized,
sharp-edged, glassy particles resulting from an explosive volcanic eruption.
volcanic cinder A pyroclastic fragment, 0.5 to 2.5 cm in diameter,
formed as magma spatters into the air during a volcanic eruption and cools as
it falls to Earth.
volcano A vent in the
surface of the Earth, from which lava, ash, and gases erupt, forming a
structure that is roughly conical.
volcanogenic massive sulfide deposit A mineral deposit
of metallic sulfides formed directly through processes associated with
volcanism, commonly in a submarine setting.
vulnerable mineral A mineral that
does not easily resist decomposition .
Wadati-Benioff zone An inclined
plane, roughly coincident with a subduction zone, along which the foci
of earthquakes cluster.
Waste Isolation Pilot Plant A pilot plant
near Carlsbad, New Mexico, for the storage of low level nuclear waste.
water gap A gap in a ridge
or mountain through which a stream flows.
water power Power generated
through the agency of moving water.
water table The surface
between the zone of saturation and the zone of aeration.
waterfall The perpendicular
or very steep descent of a stream.
wave base A depth equal to
one half the wave length of waves in deep water, below which stirring due to
wind is negligible.
wave crest The top of a
wave.
wave height The vertical
distance between the crest and adjacent trough of a wave.
wave length The distance
between two successive wave crests or troughs.
wave trough The low
spot between two successive waves.
weathering The process by
which Earth materials change when exposed to conditions at or near the Earth's
surface and different from the ones under which they formed. compare decomposition , disintegration .
welded tuff A pyroclastic rock in which glassy clasts have been
fused by the combination of the heat retained by the clasts, the weight of
overlying material, and hot gases.
well An artificial intersection of the
surface and the water table.
Wilson Cycle The opening and
closing of ocean basins through plate tectonics.
wilting point The stage at
which all water available to plants has been used.
wind farm An area in which
a large number of windmills have been erected to generate electrical power.
wind gap An abandoned water
gap.
wind power Power generated
by using the force of the wind.
wind shadow An area of quiet
air in lee of an obstacle. Zone of sand accumulation in lee of sand dune.
xenolith see inclusion
X-ray diffraction The diffraction
of a beam of X-rays by the three dimensional periodic array of atoms in a crystal structure . The identity and arrangement
of atomic in the structure can be determined by interpreting the angles at
which X-rays are scattered by the structure and the intensities of scattered
beams.
yardang Sharp,
irregularly-crested ridges carved by wind and oriented parallel to wind.
yazoo-type river A tributary
stream unable to enter a main stream because of natural levees along the main stream. It flows in a backswamp area, parallel to the main stream until
it finds an entry to the main stream.
yield point The stress limit
at which permanent deformation takes place in a non-brittle material.
Yucca Mountain Site Site in Nevada
proposed for the storage of high level nuclear waste.
zone of ablation The area of
wastage in a glacier.
zone of accumulation 1. The B horizon
in a residual soil. 2. The area in which ice accumulates in a glacier.
zone of aeration Zone immediately
below the ground surface within which pore spaces are partially filled with
water and partially filled with air.
zone of flow The zone in a
glacier that flows by deforming along planes of weakness in the ice crystals.
zone of fracture The near surface
zone in a glacier that behaves like a brittle substance.
zone of leaching The upper
horizons in a soil, through which gravitational moisture travels, removing
soluble decomposition products.
zone of saturation The zone below
the zone of aeration in which all pore spaces are filled with
water.
Original Source of This Glosary: http://www.geology.iastate.edu/new_100/glossary.v2.html
Hatalar için : aksari@boun.edu.tr