aa:a blocky or rubbly basaltic lava flow. (Please note that this definition was inverted with pahoehoe in the first version of this glossary).
accretionary wedge: A peice of continental crust that is accreted or attached to a larger mass.
aeolian: wind deposited an in desert sands.
aesthenosphere: literally "weak sphere" the region of the mantle below the lithosphere. This region of the mantle undergoes plastic deformation, but is too weak to have brittle deformation that causes eathquakes.
amorphous: Non-crystalline; lacking a crystal structure; a solid such as glass, opal, wood, coal, that lacks an ordered atomic arrangement.
anion: A negatively charged atom; an atom with more electrons than protons.
anticline: A concave-downward fold, i.e. the limbs are depressed and the center raised.
aquifer: A porous and permeable layer below the water table.
aquitard: An impermeable layer below the water table that retards the flow of water.
arete: A narrow ridge separating two cirque valleys.
artesian: free-flowing; the pressure in an aquifer exceeds the water column of the burial depth, and the water flows onto the surface without pumping.
ash flow: A flow or deposit of (usually) silicic volcanic ash as a result of an explosive eruption.
atmophile: A geochemical class of elements that form vanderWaals bonds and are highly volatile and depleted in the Earth relative to cosmic (solar)abundances.
atomic number: The number of protons in the nucleus of a particular element; the charge on the nucleus.
atomic weight: The average mass number of a particular element; the mass (in grams) of Avagadros number of atoms of an element.
avalanche: an air-fluidized slide of snow, ice, or rock and soil debris. The slide may travel at speeds in excess of 100 mph and become airborne in places.
badland: A deeply gullied terrain in horizontally bedded rock in unvegetated arid or semiarid terrain.
barchan: A crescent-shaped dune with limbs downwind.
basalt: a volcanic igneous rock that is low in silica (40-50%), and high in Fe and Mg. It is produced by partial melting of the mantle, and forms the bulk of the oceanic crust and may also occur in continenetal environments.
basin: A low-lying area of low relief.
baymouth bar: A narrow strip of sand closing a bay off from the ocean.
batholith: A large (>100km2 exposed body of plutonic igneous rock.
bed load: The sediment transported by a stream that is dragged or bounced along the bottom.
bedding: a series of visible layers in a rock that reflect the original surfaces on which sediemnts were deposited.
Benioff zone: A zone in the upper mantle, usually beneath an oceanic trench, where a cool, brittle plate, being subducted back into the mantle, gives rise to deep earthquakes.
bergschrund: A crevasse formed at the head of a cirque valley as the glacier ice pulls away from the ice attached to the mountain.
blowout dune: A crescent-shaped dune with limbs upwind (same as parabolic dune).
blueschist: a high pressure, low temperature metamorphic rock characteristic of subduction zones.
boulder: a large rock greater than 256mm (10") in diameter.
breccia: a sedimentary rock containing abundant angular pebble, cobble, and boulder-sized particles.
butte: A small (<~10ac), conspicuous, isolated hill bounded by cliffs.
cation: A positively charged atom; an atom with fewer electrons than protons.
chalcophile: A geochemical class of elements that form covalent bonds,commonly occur in sulfide minerals, and depleted in the Earth relative to cosmic (solar)abundances.
chondrite: A type of primitive stoney meteorite containing chondrules, quenched droplets of early condensates from the solar nebula.
cinder cone: A small volcanic cone built up around a basaltic vent.
cirque: A bowl-shaped valley at the head of a glacier.
clay: A particle less than 0.004mm (4 micrometers) in diameter. Also a group of layer-silicate minerals characterized by poor crystallinity and fine particle size.
cobble: a rock particle 64 to 256mm in diameter.
conglomerate: a sedimentary rock containing abundant, rounded pebble, cobble, and boulder-sized particles.
convection: the vertical circulation of a fluid in response to uneven heat distribution.
convergent boundary: A plate boundary at which plates approach eachother.
core: The region o fthe Earth's interior below a depth of 2900 km which is composed of liquid (outer) and solid (inner) metallic iron-nickel.
craton: The old, stable, interior portion of a continent.
creep: the imperceptably slow movement of soil downslope under the force of gravity.
crevasse: A deep tensional fracture formed on a glacier.
cross bedding: A sedimentary rock texture characterized by overlapping and cross-cutting bedding, typical of aeolian sands.
crust: the region of the earth from the surface to the Moho. The crust is part of the lithosphere and undergoes brittle deformation that causes earthquakes.
The crust is divided into continetal crust which is thick, (30 - 60km) light,
silica-rich, and old, and oceanic crust which is thin (<20km) dense, silica-poor, and young.
cuesta: An asymmetric hill or ridge with a gentle slope on one side and a steep outcrop slope on the other.
debrisflow: a water-fluidized flow of rock and soil debris, typically on slopes steeper than 20 degrees and leaving a narrow incised channel with debris levees.
deflation: Removal of fine particles by wind erosion.
desert: A region that receives less than 25cm (10in) of rain per year.
desert pavement: A pebble/cobble strewn surface of a desert that results from deflation.
dike: A small, discordant (injected into massive igneous, metamorphic, or across layers of sedimentary rock) body of intrusive igneous rock.
dip: An angle giving the orientatio n of a planar feature such as bedding or a fault plane; it is the acute angle measured between the planar feature and the horizontal. It is measure perpendicular to the strike direction.
divergent boundary: A plate boundary at which the plates are moving apart as a result of spreading.
dolomite: A rhombohedral carbonate mineral of formula CaMg(CO3)2. A rock composed predominantly of the mineral dolomite.
drainage basin: The total area drained by a stream.
drainage divide: The boundary between two drainage basins.
drumlin: A low, rounded, elongate hill or ridge of compact till left by a glacier.
earthquake: A trembling or shaking of the ground caused by a sudden release of energy stored in the rocks beneath the earth's surface.
eclogite A high pressure, high temperature metamorphic rock composed predominantly of garnet and clinopyroxene and which is compositionally equivalent to basalt.
electron A fundamental subatomic particle having an electric charge of -1 and a rest mass of 9.11 x 10-28 gm.
epicenter: The point on the surface of the earth's surface directly above the focus or release point of an earthquake.
erosion: The physical transport of unconsolidated materials at the earth's surface by wind and water.
esker: A low sinuous ridge of sand and gravel left by a subglacial stream.
evaporite: A sedimentary rock formed by evaporation of sea water. A typical evaporite sequence of minerals is 1)calcite (CaCO3, 2) gypsum CaSO42(H2O), 3) halite (NaCl), and 4) sylvite (KCl).
exotic terrane: A piece of continental crust of exotic or different origin than the main mass.
fault: a fracture in rock on which movement has taken place.
felsic: opposite of mafic; "rich in feldspar"; a term applied to magmas or igneous rocks that are silica-rich as rhyolites or granites.
ferromagnesian: Minerals or rocks that are rich in iron (Fe) and magnesium (Mg), such as olivine and pyroxene.
fjord: A long, narrow, U-shaped, glacier-carved inlet from the ocean.
foliation: A rock texture formed by alignment of sheet-like features or grains.
focus: (Seismology) The actual point or plane of rupture of an earthquake.
fractional crystallization: The process of enriching a magma in silica by early crystallizing mafic minerals that drop to the bottom of the magma chamber.
geyser: a hot spring that undergoes periodic catastrophic boiling (erupting).
glacier: large permanent mass of ice that forms on land and moves downhill under the force of gravity.
gneiss: a high grade metamorphic rock with well developed lineation or foliation, typically granitic in composition.
gradient: The average drop of a stream in ft/mi (USA) or m/km (world).
granite: an intrusive (plutonic) igneous rock of hig silica (SiO2) content typical of continental regions.
granulite: a high grade metamorphic rock with an equant texture (no foliation or lineation).
groundwater: liquid water that lies below the surface in fractures and porespace in rocks.
hogback: A narrow ridge formed by the outcrop near-vertical sedimentary beds.
horn: A high, sharp-pointed, steep sided, pyramidal mountain peak formed by glacial erosion.
hornfels: a high temperature, low pressure metamorphic rock typically with an equant texture (no foliation or lineation).
hydration: a chemical rection by which water or hydrogen is added to a compound or mineral. This usually disrupts the crystalline structure of a mineral.
hydrologic cycle: The movement of water from the ocean by evaporation, over land, precipitation and transport back to the ocean as surface and ground water.
hydrostatic: equal in all directions as pressure under water.
hydrothermal: formed by precipitation from hot aqueous solutions.
ice cap: A mountain glacier that flows outward in several directions.
ice sheet: A large mass of ice covering a significant portion of a continent as in Greenland and Antarctica.
inner core: The innermost portion of the core which is composed of solid iron-nickel metal.
ion: A charged atom; an atom with more or fewer electrons than protons.
isomorph: Two compounds that have the same crystal structure, but diferent compositions. Examples: halite/sylvite, forsterite/fayalite, halite/galena.
isostacy: The principal of gravitational balance or equilibrium.
joint: A fracture in rock on which no movement has taken place.
karst: A type of topography marked by sinkholes, springs, disappearing streams indicating underground drainage in limestone caverns.
landslide: a large flow of rock, soil, and debris, typically slow-moving.
laterite: A soil typical of tropical rain forests characterized by extreme leaching and removal of soluble elements.
lava: A magma that is on the surface (i.e. volcanic).
limestone: a sedimentary rock made up predominantly of calcite.
lineation: A rock texture formed by alignment of rod-like features or grains.
lithification: The solidification of sediments to form sedimentary rocks.
lithophile: A geochemical class of elements that form ionic bonds,commonly occur in oxygen minerals, and are enriched in the Earth's crust relative to cosmic (solar)abundances.
lithosphere: The near-surface region of the crust and uper mantle that undergoes brittle fracture.
loess: An aeolian deposit of angular sand-, silt- and clay-sized particles.
load: The total sediment transported by a stream.
longitudinal dune: A sand dune that forms as a ridge parallel to the wind direction.
lower mantle: The lower and largest portion of the mantle extending from a depth of 670km to 2900km. It composes approximately 50% of the mass of the planet.
mafic: A term applied to igneous rocks that are rich in ferromagnesian minerals or low in silica as basalt or gabbro.
magma: Any molten rock.
mantle: The region of the Earth from the base of te crust (Moho) to the core-mantle boundary at a depth of ~2900km. It is composed of solid silicate rock.
marble: metamorphised limestone, a metamorphic rock composed predominantly of calcite.
mass number: The number of protons plus neutrons in the nucleus of a particular isotope of an element.
mesa: A relatively small flat-topped hill or mountain.
metamorphism: The solid-state transformation of pre-existing rock into texturally or mineralogically distinct new rock as the result of high temperature, high pressure, or both.
metasomatism: Chemical alteration of a rock by the action of hydrothermal fluids.
migmatite: A high grade metamorphic rock that has undergone partial melting, typically with segregations of K-feldspar.
mineral: a naturally occurring homogeneous solid of definite
chemical composition and ordered atomic arrangement. It is usually formed
by inorganic processes; a natural crystalline phase.
Moho The Mohorivicic discontinuity (seismic reflector) at the base of the crust.
monocline A fold in rock connecting two vertically offset, horizontal sections of sedimenary rocks.
moraine A deposit of till (rock and soil) left by a glacier.
mountain A large mass of rock projecting abouve surrounding terrain.
mudstone A sedimentary rock made up of clay-sized particles, typically massive and not fissile.
neutron A fundamental subatomic particle having an electric charge of 0 and a rest mass of 1.67 x 10-24 gm.
obsidian: A dense, usually black, volcanic glass.
ogive: A compressional wave on the surface of a glacier as near the bottom of an icefall.
orogenic belt: A range of mountians all formed in the same orogeny (event).