GLOSSARY OF GEOLOGICAL TERMS-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.
Posted on: Tue, 26 Aug 2014 14:33:09 +0000
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