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


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

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 needle points.

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

magnetic pole
The point on the Earth

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.

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

medial moraine
Formed by the merging of lateral moraines as two valley glaciers join.

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

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

Modified Mercalli Scale
A commonly used scale of earthquake intensity.

Mohorovicic discontinuity
(Moho)

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.

neutron
A particle in the nucleus of an atom, which is without electrical charge and with approximately the same mass as a proton.

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.

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.

oblique-slip fault
A fault with both dip-slip and strike-slip components of movement.

obliquity of the Earth
Tilt of the Earth

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.

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.

pahoehoe
A Hawaiian term for a basaltic lava flow with a smooth, or ropy surface. compare aa.

paleomagnetism
Study of the Earth

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.

Pel
A type of volcanic eruption characterized by nu

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.
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
Soil conditions prevailing in area whose mean annual temperature is 0o C.

permafrost table
The depth in a permafrost region at which the maximum temperature reaches 0o C.

permeability
The capacity of material to transmit water or other fluids.

petroleum
A general term including both oil and natural gas.

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.