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Geological Terms Beginning With "L"



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Laccolith:

An igneous intrusion that has been forced between two layered rock units. The top of the intrusion is arched upwards and the bottom of the intrusion is nearly flat.

Lahar:

A mudflow composed of water and volcanic ash. Lahars can be triggered by the flash melting of the snow cap of a volcanic mountain or from heavy rain. Lahars are very dangerous because they can occur suddenly and travel at great speeds.

Laminar Flow:

A state of uniform flow within a fluid in which the moving particles travel along parallel paths (compare with Turbulent Flow).

Landslide:

A downslope movement of rock and soil over a failure surface and under the influence of gravity. Slumps, earthflows, debris flows and debris slides are examples.

Lapilli:

Volcanic rock materials which are formed when magma is ejected by a volcano. Typically used for material that ranges between 2 and 64 millimeters in diameter.

Lateral Moraine:

An accumulation of till along the sides of a valley glacier that is produced by ice action.

Lava:

Molten rock material on Earth's surface.

Lava Tube:

A tunnel below the surface of a solidified lava flow, formed when the exterior portions of the flow solidify and the molten internal material is drained away.

Leaching:

The removal of soluble constituents from a rock or soil by moving ground water or hydrothermal fluids.

Lease Bonus:

Money paid to a mineral rights owner in exchange for granting a lease. This payment may be in addition to any rental or royalty payments.

Left-Lateral Fault:

A fault with horizontal movement. If you are standing on one side of the fault and look across it the block on the opposite side of the fault has moved to the left. (Also see Right-Lateral Fault.)

Levee:

A long continuous ridge built by people along the banks of a stream to contain the water during times of high flow. Natural levees can also be built along the banks of a stream. When the flood water decelerates upon leaving the channel, sediments quickly drop out of suspension and build a ridge over time.

Limb:

One side of a fold. The dipping rock units between the crest of an anticline and the trough of a syncline.

Limestone:

A sedimentary rock consisting of at least 50% calcium carbonate (CaCO2) by weight. Picture of Limestone.

Lineament:

A straight topographic feature of regional extent which is thought to represent crustal structure. A fault, line of sinkholes, straight stream stretch or a line of volcanoes can be considered linear features.

Liquefied Natural Gas (LNG):

Natural gas that has been converted to the liquid state by reducing its temperature. (At standard surface temperature and pressure the liquification temperature is about -260 degrees Fahrenheit.)

Lithification:

The processes through which sediments are converted into sedimentary rock, including compaction and cementation.

Lithology:

The study and description of rocks, including their mineral composition and texture. Also used in reference to the compositional and textural characteristics of a rock.

Lithosphere:

The rigid outer shell of the earth which includes the crust and a portion of the upper mantle.

Lithospheric Plate:

A large slab of the lithosphere that can be moved by convection current motion within the mantle.

Load:

The total amount of sediment being carried by a stream or a glacier. Includes suspended materials, dissolved materials and materials moved along Earth's surface. (Also see: bed load, dissolved load, suspended load.)

Lode:

A rich accumulation of minerals in solid rock. Frequently in the form of a vein, layer or an area with a large concentration of disseminated particles. (See placer deposit for contrast.)

Longitudinal Dune:

A long, narrow sand dune that has its long dimension oriented parallel to the direction of the wind.

Longitudinal Profile:

A cross section of a stream or valley beginning at the source and continuing to the mouth. These profiles are drawn to illustrate the gradient of the stream.

Longshore Current:

A flow of water parallel to a coastline that is caused by waves striking the coast at an oblique angle.

Longshore Drift:

The movement of sediment along a coastline caused by waves striking the coast at an oblique angle. The waves wash sediment particles up the beach at an oblique angle and the swash back to the sea carries the particles down the gradient of the beach. This produces a zig-zag path of particle movement along the beach.

Lowland:

A relatively flat area in the lower levels of regional elevation.

Low-Velocity Zone:

A zone within the upper mantle where seismic wave velocities are relatively low. This zone is located about 35 to 155 miles below the surface.

Luster:

The manner in which light reflects from a mineral surface. Metallic, submetallic and non-metallic are the basic types of luster.

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