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Iowa State University - Geology terms Category: Education > University Date & country: 18/11/2013, USA Words: 782

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
A measure of the circularity of the Earth

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

electron shell
A characteristic energy level with which an electron is associated. Electrons occupy discrete shells within the cloud surrounding an atom

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

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.

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

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 nu

firn
(n

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.

fjord
Glaciated valleys now flooded by the sea.

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.

fold and thrust mountains
Mountains, characterized by extensive folding and thrust faulting, that form at convergent plate boundaries on continents.

foliation
A planar structure that develops in metamorphic rocks as a result of directed pressure.

foot wall block
The body of rock that lies below an inclined fault plane. compare hanging wall block

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.

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.

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

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.

geology
The science that deals with the study of the planet Earth

geosyncline
A downwarping of the Earth

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.

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 .