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Of or associated with lakes.

Lagerstätte (pl. Lagerstätten)

Fossil deposit containing animals or plants that are preserved unusually well, sometimes even including the soft organic tissues. Lagerstätten form in chemical environments that slow decay of organic tissues or enhance preservation through mineralization. Also, quick burial of the organism leaves no opportunity for disturbance of the fossils. Lagerstätten are important for the information they provide about soft-bodied organisms that we otherwise would know nothing about.


A pyroclastic debris flow or mudflow that typically flows down river valleys after a volcanic eruption. Lahars can be very destructive, as they can reach thicknesses of over 140 meters (460 feet) and travel at tens of meters (yards) per second.
See also: debris flow, pyroclastic, volcanism

Lake Superior agate

The Minnesota state gemstone. This stone formed in magma containing bubbles created by water and carbon dioxide that had been trapped in the magma. After the magma cooled, these bubbles were slowly filled by mineral-rich water, depositing layers of fine quartz crystals and enough iron to color the resulting rocks red.
See also: iron, magma, quartz


An ultramafic volcanic (extrusive) rock with high levels of potassium and magnesium that contains coarse crystals. Diamonds can occur in lamproites.


The rapid slipping of a mass of earth or rock from a higher elevation to a lower level under the influence of gravity and water lubrication. Landslides include rock falls, avalanches, debris flows, mudflows, and the slumping of rock layers or sediment.
See also: mass wasting

Laramide Orogeny

A period of mountain building that began in the late Cretaceous, and is responsible for the formation of the Rocky Mountains.
See also: orogeny

last glacial maximum

The most recent time the ice sheets reached their largest size and extended farthest toward the equator, about 26,000 to 19,000 years ago. Ice sheets over North America melted back until about 10,000 years ago—they have been relatively stable since that time.

Laurentide Ice Sheet

An ice sheet that covered most of Canada during the last major glaciation. In its prime, the Laurentide was more than 5 kilometers (3.1 miles) thick at its thickest point on what is now the Hudson Bay. The sheet began to melt about 13,000 years ago.


Molten rock located on the Earth’s surface. When magma rises to the surface, typically through a volcano or rift, it becomes lava.
Lava cools much more quickly than magma because it is at the surface, exposed to the atmosphere or ocean water where temperatures are much cooler. Such rocks, with little time to crystallize, have small or no crystals.

lava tube

A natural tube formed by lava moving beneath the hardened surface of a lava flow.

Law of Superposition

The geologic principle that states that unless rock layers have been overturned or intruded, older rocks are found at the bottom and younger rocks are found at the top of a sedimentary sequence.
See also: stratigraphy


A metallic chemical element (Pb).
Lead was one of the first metals mined in North America, where it was sought after especially for making shot. It is used in batteries, communication systems, and building construction.


Downwind; facing away from the wind (not subject to orographic precipitation, and thus dryer).


A soft, waxy dark colored mineraloid found in association with near-surface lignite deposits. It is an oxidation product of lignite, and is used as a soil conditioner, a stabilizer in water treatment, and as a drilling additive.


A deposit of sediment built up along and sloping away from the sides of a river’s floodplain ; also, an artificial embankment along a waterway to prevent flooding, especially from a river.


A soft, brownish-black coal in which the alteration of plant matter has proceeded farther than in peat but not as far as in bituminous coal.


An inorganic white or grayish-white compound made by roasting limestone ( calcium carbonate, CaCO3) until all the carbon dioxide (CO2) is driven off. Originating from limestone, dolomite, or marble, lime is very important to agriculture, in which it is regularly applied to make soils “sweeter” (less acidic).


A sedimentary rock composed of calcium carbonate (CaCO3). Most limestones are formed by the deposition and consolidation of the skeletons of marine invertebrates; a few originate in chemical precipitation from solution.
Limestone is ordinarily white but can be colored by impurities such as iron oxide (making it brown, yellow, or red), or organic carbon (making it blue, black, or gray). The rock’s texture varies from coarse to fine.


A process by which water-saturated unconsolidated sediment temporarily loses strength and behaves as a fluid when vibrated.


The process of creating sedimentary rock through the compaction or cementation of soft sediment. The word comes from the Greek lithos, meaning “rock.”


A metallic chemical element (Li) used in the manufacture of ceramics, glass, greases, and batteries.


The outermost layer of the Earth, comprising a rigid crust and upper mantle broken up into many plates.
The plates of the lithosphere move with the underlying asthenosphere, on average about 5 centimeters (2 inches) per year and as much as 18 centimeters (7 inches) per year.

littoral cone

A volcanic ash or tuff cone formed when a lava flow runs into a body of water; "littoral" refers to nearshore.
See also: lava, tuff, volcanic ash, volcanism


A soil containing equal amounts of clay, silt, and sand.


An ore deposit that fills a fissure or crack in a rock formation; alternately, an ore vein that is embedded between layers of rock.


Very fine-grained, wind-blown sediment, usually rock flour left behind by the grinding action of flowing glaciers.


The emission of light.


A physical property of minerals, describing the appearance of the mineral’s surface in reflected light, and how brilliant or dull it is. Luster can range from metallic and reflective to opaque, vitreous like glass, translucent, or dull and earthy.


An extinct, terrestrial tree belonging to the plant division Lycopodiophyta, and characterized by a tall, thick trunk covered with a pattern of diamond-shaped leaf scars, and a crown of branches with simple leaves. Lycopods, or "scale trees," grew up to 98 feet (30 meters) high in Mississippian and Pennsylvanian forests.
The plant division Lycopodiophyta survives today but only as very small plants on the forest floor, sometimes called “ground pines.”