Geological Glossary - L

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La Nina	La Nina is the cold phase of an extensive cycle of atmospheric and oceanic conditions called the El Nino/Southern Oscillation (ENSO) cycle. La Nina is marked by cold currents off Peru.
Lake Missoula	Glacial lake whose flood when its ice damn broke created the Grand Coulee. Glaciers impounded Clark Fork River.
Lg wave	A surface wave which travels through the continental crust.
Love wave	A major type of surface wave having a horizontal motion that is shear or transverse to the direction of propagation (travel). It is named after A.E.H. Love, the English mathematician who discovered it.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
laccolith	A sill-like igneous intrusion that forces apart two strata and form a round, lens-shaped body many times wider than it is thick.
lahar	A torrential flow of water-saturated volcanic debris down the slope of a volcano in response to gravity. A type of mudflow. Also known as a glowing avalanche.
laminar flow	A flow regime in which particle paths are straight or gently curved and parallel.
lamination	Very thin layer of less than 1 cm thickness.
land-use	Present and historical uses of land, such as for agriculture, mining, recreation and grazing.
landslide	An abrupt movement of soil and bedrock downhill in response to gravity. Landslides can be triggered by an earthquake or other natural causes. Undersea landslide can cause tsunami.
langley	The unit of solar energy relating to the amount which reaches a specific area of the earth's surface.
lapilli	A fragment of volcanic rock formed when magma is ejected into the air by expanding gases. The size of the fragments ranges from sand- to cobble-size.
large-ion lithophile elements	Elements with an affinity for oxygen-containing compounds, particularly silicate mineral, and possessing ionic radii larger than most common rock-forming elements. Examples include K, Cs, Th, U, La, Ba.
lateral moraine	A moraine formed along the side of a valley glacier and composed of rock craped off or fallen from the valley sides.
lateritization	Soil-forming process typical of warm humid climates where in mature landscapes, primary mineral are essentially completely weathered away to form red soil (laterites) of high aggregate stability composed primarily of sesquioxides (oxides and hydroxides of iron and aluminum).
latitude	The location of a point north or south of the equator. Latitude is shown on a map or globe as east-west lines parallel to the equator.
lava	Magma which has reached the surface through a volcanic eruption. The term is most commonly applied to streams of liquid rock that flow from a crater or fissure. It also refers to cooled and solidified rock.
lava flow	An outpouring of lava onto the land surface from a vent or fissure. Also a solidified tongue-like or shee- like body formed by outpouring lava.
lava tube	A tunnel formed when the surface of a lava flow cools and solidifies, while the still-molten interior flows through and drains away.
layer	A bed or stratum of rock.
leaching	The removal of elements from a soil by dissolution in water moving downward in the ground.
leaking mode	A surface seismic wave which is imperfectly trapped so that its energy leaks or escapes across a layer boundary, causing some attenuation or loss of energy.
left-lateral fault	A strike-slip fault on which the displacement of the far block is to the left when viewed from either side.
levee	"A low ridge along a stream bank, formed by deposits left when floodwater decelerates on leaving the channel; also an artificial barrier to floods built in the same form. "
lichenometry	A dating method that uses the growth rate of certain lichen species as an indicator of the age of the surface the lichen is growing on.
limb	The relatively planar part of a fold or of two adjacent folds (for example, the steeply dipping part of a stratum between an anticline and syncline).
limb, celestial	"The edge of a celestial body as it appears to an observer; the edge of the sun's disk, for example."
limestone	A sedimentary rock made mostly of the mineral calcite (calcium carbonate). Limestone is usually formed from shells of once-living organisms or other organic processes, but may also form by inorganic precipitation.
limestone	A sedimentary rock made mostly of the mineral calcite (calcium carbonate CaCO2). Limestone is usually formed from shells of once-living organisms or other organic processes, but may also form by inorganic precipitation.
limonite	A mineral composed of iron oxides and water. Rust. Very common in many rocks after weathering at the Earth’s surface. Imparts brown or yellow color to many rocks.
lineament	A linear (relatively straight) topographic feature or features such as a fault, line of dense vegetation, or a chain of aligned volcanoes.
lineation	Any linear arrangement of features found in a rock.
liquefaction	The process in which a solid (soil) takes on the characteristics of a liquid as a result of an increase in pore pressure and a reduction in stress.
liquid of descent	In a graph of chemical composition, a line connecting magma related by differentiation to a common parent. The chemical expression of magmatic evolution.
lithification	The conversion of loose sediment into solid sedimentary rock. Several processes, including compaction of grain, filling of spaces between grains with mineral cement, and crystallization act to solidify sediment.
lithology	The systematic description of rocks, in terms of mineral composition and texture.
lithosphere	The component of the Earth's surface comprising the rock, soil and sediment. It is a relatively passive component of the climate system and its physical characteristics are treated as fixed elements in the determination of climate. Semirigid upper platelike layer of the earth. Its thickness is near zero at oceanic ridge axes, but it increases with age to about 100 km. Oceanic lithosphere consists of a crustal layer ~5 km thick of basaltic composition underlain by mantle rocks. Continental lithosphere consists of a layer of crustal rock 30-60 km thick of low density and variable composition underlain by mantle rocks. In plate tectonics, an outer layer of great strength relative to the underlying asthenosphere for deformation at geologic rates. It includes the crust and part of the upper mantle and is about 100 km thick.
lode	An unusually large vein or set of veins containing ore mineral.
loess	A buff-colored, wind-blown deposit of fine silt, which is frequently exposed in bluffs with steep faces. The thickness can range from 6 to 30 m. The loess of the United States and Europe is thought to be the fine materials first transported and deposited by the waters of melting ice sheet during the glacial period. It was later blown considerable distances with in some cases deposition in lakes. The origin of Asiatic loess however is apparently wind-blown dust from central Asian deserts.
long-period event	Discrete events with nearly monotonic, low-frequency (1-5 Hz) waveforms that resonate for many cycles.
longitude	The location of a point east or west of the prime meridian. Longitude is shown on a map or globe as north-south lines left and right of the prime meridian, which passes through Greenwich, England.
longitudinal dune	A long dune parallel to the direction of the prevailing wind.
longitudinal profile	A cross section of a stream from its mouth to its head, showing elevation versus distance to the mouth.
longshore current	A current that moves parallel to a shore and is formed from the momentum of breaking wave that approach the shore obliquely.
longshore drift	The movement of sediment along a beach by swash and backwash of wave that approach the shore obliquely.
lopolith	A large laccolith that is bowl-shaped and depressed in the center, possibly by subsidence of an emptied magma chamber beneath the intrusion.
low-frequency event	General term for discrete events with either enriched low frequencies or deficient high frequencies compared to typical earthquake.
low-velocity zone	A region in the Earth, especially a planar layer, that has lower seismic-wave velocities than the region immediately above it.
low-velocity zone	Any layer in the Earth in which seismic wave velocities are lower than in the layers above and below.
lowland	Land of general low relief at the lower levels of regional elevation.
luster	The general textural impression of a mineral surface, given by the light reflected from it. Terms such as metallic, submetallic are standardized but subjective.