Lake

Lakes are inland bodies of standing water. Although millions of lakes are scattered over Earth's surface, most are located in higher latitudes and mountainous areas. Canada alone contains almost 50 percent of the world's lakes. Lakes can be formed by glaciers, tectonic plate movements, river and wind currents, and volcanic or meteorite activity. Some lakes are only seasonal, drying up during parts of the year.

The study of lakes, ponds, and other freshwater bodies is called limnology (pronounced lim-NOL-o-gee). Although ponds are considered small, shallow lakes, there is one important difference between the two bodies of water: temperature. Ponds generally have a consistent temperature throughout, whereas lakes have various temperature layers, depending on the season.

The Great Lakes of the United States and Canada are the world's largest system of freshwater lakes. Lake Superior, the northernmost of the Great Lakes, is the world's largest freshwater lake with an area of 31,820 square miles (82,730 square kilometers). Lake Titicaca in the Andes Mountains on the border between Peru and Bolivia is the world's highest large freshwater lake at 12,500 feet (3,800 meters) above sea level.

Some freshwater lakes become salty over time, especially in arid regions. Because the water in these lakes evaporates quickly, the salt from inflowing waters reaches a high concentration. Among the world's greatest salt lakes are the Caspian Sea, Dead Sea, and Great Salt Lake. Covering an area of about 144,000 square miles (372,960 square kilometers), the Caspian Sea is the largest lake in the world. At 1,292 feet (394 meters) below sea level, the Dead Sea is the lowest lake in the world.

Origins of lakes

Most lakes on Earth were formed as a result of glacier activity. Earth's glacial ice formed and extended into what is now Canada, the northernmost United States, and northern Europe. As the heavy, thick ice pushed along, it created crevices by scouring out topsoil and even carving into bedrock (the solid rock that lies beneath the soil). Glacial growth peaked about 20,000 years ago, after which time the ice slowly began to melt. As the ice melted, the glaciers retreated, but the basins formed by glaciers remained and filled with water from the melting glaciers.

Movements of Earth's crust, water, and wind can also form lakes. The moving of the plates that compose Earth's crust (called tectonic activity) often forms basins, especially along fault lines (where plates meet and move against each other). These basins or depressions fill with water, forming lakes such as Lake Baikal in Siberia.

Words to Know

Blowout: Lake basin created in coastal or arid region by strong winds shifting sand.

Caldera: Volcanic crater that has collapsed to form a depression greater than 1 mile (1.6 kilometers) in diameter.

Eutrophication: Natural process by which a lake or other body of water becomes enriched in dissolved nutrients, spurring aquatic plant growth.

Limnology: Study of lakes, ponds, and other freshwater bodies.

Oxbow lake: Lake created when a loop of a river is separated from the main flow by gravel, sand, and silt deposits.

Solution lake: Lake created when groundwater erodes bedrock, resulting in a sinkhole.

Turnover: Mixing and flip-flopping of the differing temperature layers within a lake.

Water currents and land erosion by water form oxbow and solution lakes. Oxbow lakes are created when winding rivers such as the Mississippi change course, carrying water through twists and turns that form loops. As deposits build up and separate a loop from the main flow of the river, an oxbow lake such as Lake Whittington in Mississippi forms. Solution lakes result from groundwater eroding the bedrock above it, creating a sinkhole. Lakes from sinkholes are the predominant type in Florida and on Mexico's Yucatan Peninsula. Wind can also create lake basins called blowouts, which usually occur in coastal or arid regions. Blowouts created by shifted sand are typical in northern Texas, New Mexico, southern Africa, and parts of Australia.

A few lakes are formed by volcanic activity or meteors. After erupting, some volcanoes collapse, forming basins that collect water. Volcanic basins with diameters greater than one mile are called calderas. Crater Lake in Oregon (the seventh deepest lake in the world) is a caldera 1,932 feet (590 meters) deep, 6 miles (10 kilometers) long, and 5 miles (8 kilometers) wide. The largest meteorite-formed lake in the world is found in New Quebec Crater (formerly Chubb Crater) in northern Quebec, Canada. It is 823 feet (250 meters) deep inside a crater about 2 miles (3 kilometers) wide.

Water circulation

Water circulation is the mixing of water in a lake. When the three temperature layers of a lake mix and change places, a lake is said to undergo

turnover. Turnover occurs when water in an upper layer is denser, or heavier, than the layer of water underneath it. Cooler water tends to be denser than warmer water. Deeper water is generally both denser and colder than shallow water.

In autumn, the upper layers of a lake cool down because of the cooling air above. Eventually, these layers, mixed by winds, cool to a temperature lower than that of the layer at the bottom of the lake. When this occurs, the lowest layer rises to the surface, mixing with the other layers. This process is called fall turnover.

In spring, ice covering a lake melts and mixes with the upper layer, which then becomes denser than the layers beneath. Mixing takes place and the whole lake turns over. This is spring turnover.

Lake threats

Pollution is the major threat to the life of a lake. Acid rain is formed by sulfates and nitrates emitted from coal-burning industries and automobile exhaust pipes. These chemicals combine with moisture and sunlight in the atmosphere to form sulfuric and nitric acids that enter lakes via rain and other precipitation. Acid rain is 10 times more acidic than normal rain. When a freshwater lake becomes too acidic, its life-forms gradually die. Other chemical pollutants include fertilizers and pesticides, which enter lakes through soil run-offs into streams. Pesticides are toxic to fish, while fertilizers can cause eutrophication (pronounced YOU-trofi-KAY-shun).

Eutrophication is the natural process by which a lake or other body of water becomes enriched in dissolved nutrients (such as nitrogen and phosphorus) that spur aquatic plant growth. Increased plant growth leads to an increase in the organic remains on the bottom of a lake. Over time, perhaps centuries, the remains build up, the lake becomes shallower, and plants take root. Finally, as plant life fills in the water basin, the lake turns into a marsh and then a meadow.

Chemical pollutants, including phosphorous and nitrogen compounds, can artificially accelerate this aging process. The growth of algae and other plant life is overstimulated, and they quickly consume most of the dissolved oxygen in the water. Soon, the lake's oxygen supply is fully depleted and all life in it dies.

[See also Eutrophication; Ice ages; River; Water ]

lake inland body of standing water occupying a hollow in the earth's surface. The study of lakes and other freshwater basins is known as limnology. Lakes are of particular importance since they act as catchment basins for close to 40% of the landscape, supply drinking water, generate electricity, are used to irrigate fields, and serve as recreational areas.

The Environment of Lakes

The primary source of lake water is precipitation that may enter the depression directly, as runoff from surrounding higher ground, or through underground springs. Unique flora and fauna live around a lake and vary depending on the size and shape of the lake and the surrounding rocks and soil. Flora and fauna in the lake are usually found in three zones: the littoral zone closest to the shallow water shore; the limnetic, in the open, well-lit water away from most vegetation; and the lower profundal zones areas of low oxygen and light.

Ponds are generally small, shallow lakes; the criterion for differentiating between ponds and lakes is usually temperature. Ponds have a more consistent temperature throughout; while lakes, because they are deeper, have a stratified temperature structure that depends on the season.

Global Distribution of Lakes

Lakes are not evenly distributed on the earth's surface; most are located in high latitudes and mountainous regions. Canada alone contains nearly 50% of the world's lakes. Although lakes are usually thought to be freshwater bodies, many lakes, especially in arid regions, become quite salty because a high rate of evaporation concentrates inflowing salts. The Caspian Sea, Dead Sea, and Great Salt Lake are among the greatest of the world's salt lakes. The Great Lakes of the United States and Canada is the world's largest system of freshwater lakes. Lake Superior alone is the world's largest freshwater lake with an area of 31,820 sq mi (82,414 sq km), although there is a larger volume of freshwater in Lake Baykal. The Caspian Sea is the largest lake in the world, with an area of c.144,000 sq mi (372,960 sq km). Lake Titicaca in the Andes Mts. of South America is the world's highest large lake at 12,500 ft (3,800 m) above sea level; the Dead Sea is the lowest at 1,345 ft (410 m) below sea level.

Formation and Fate of Lakes

Many lakes were formed as a result of glacial action during the Pleistocene ice sheets. In some areas, as exemplified by the Great Lakes, basins were carved into bedrock by the erosive action of the advancing ice mass. Lake basins are also formed by glacial moraine deposits that dam preexisting stream valleys. Lakes also form in calderas, created by the collapse of volcanic craters. Where extensive limestone deposits underlie a region, groundwater can dissolve great volumes of the limestone, forming caves that often contain underground lakes and eventually, if the roofs collapse, leave deep lake basins. Tectonic activity in the earth's crust forms lake basins in many ways, such as fault-generating rift valleys as those found in E Africa, that often fill with water. Oxbow lakes form in abandoned stream channels in floodplains of meandering rivers. Deposition of sediment along a shoreline can cut off bays, forming coastal lagoons. Humans often form lakes by building dams across river valleys for flood control, hydroelectric generation, or recreational purposes.

Lakes are transient features on the earth's surface and generally disappear in a relatively short period of geologic time by a combination of processes (e.g., erosion of an outlet or climatic changes that bring drier conditions). In a process called eutrophication, a lake gradually fills with organic and inorganic sediment, becoming a swamp or bog, and eventually a meadow. Human activity has greatly increased the rates of eutrophication; urban and suburban land construction activities result in increased discharge of soil debris into streams draining into lakes, filling them.

Lake

The Lake (Senijextee, Gens des Lacs) lived on both sides of the Columbia River from Kettle Falls in northeastern Washington into British Columbia to the Arrow Lakes, on the Kettle River, and on the lower Kootenay River. Their culture was of the general Plateau type and they spoke an Interior Salish language. Most of them now live on or near the Colville Indian Reservation in northeastern Washington as part of the Confederated Tribes of the Colville Reservation and are generally assimilated into European-American society. Their Current population is unknown, but they probably number about three hundred.

Bibliography

Curtis, Edward (1911). The North American Indian. Vol. 11. Norwood, Mass. Reprint. Johnson Reprint Corp., 1970.

Teit, James A. (1930). The Salishan Tribes of the Western Plateau. U.S. Bureau of American Ethnology, 45th Annual Report (1927-1928), 37-396. Washington, D.C.

lake¹ / lāk/ • n. a large body of water surrounded by land: [in names] Lake Superior. ∎  a pool of liquid: the fish was served in a bright lake of spicy carrot sauce. DERIVATIVES: lake·let / -lit/ n. lake² • n. [often with adj.] an insoluble pigment made by combining a soluble organic dye and an insoluble mordant. ∎  a purplish-red pigment of this kind, originally one made with lac, used in dyes, inks, and paints.

lake in dyeing, an insoluble pigment formed by the reaction between an organic dye and a mordant . The color of a lake depends upon the mordant as well as the dye used. Generally, lakes are not as colorfast as many inorganic dyes, but their colors are more brilliant.

lake1 body of water surrounded by land; †pond, pool XIII; †pit, grave XIV. ME. lac—(O)F.— L. lacus basin, tank, lake, pool, rel. to Gr. lákkos hole, ditch, Gael., Ir. loch LOCH, OE. lagu, ON. lǫgr sea, water, OSl, loky pool, reservoir.

lake Inland body of water, generally of considerable size and too deep to have rooted vegetation completely covering the surface. The expanded part of a river and a reservoir behind a dam are also termed lakes.

Lake Wilts. Lake 1289. OE lacu ‘small stream’.

lake2 reddish pigment. XVII. unexpl. var. of LAC.

lake. See LOCH; LOUGH; LLYN.

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