Home General Knowledge GK SPECIAL TOPIC : LAKES
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Tuesday, 22 April 2014 08:28





Lakes are inland bodies of water found in natural depressions surrounded by higher ground. Lakes are extremely varied in terms of origin, occurrence, size, shape, depth, water chemistry, and other features. Lakes can be only a few hectares in surface area (i.e., less than a square kilometer), or they can be thousands of square kilometers.

Their average depth can range from a few meters to more than a thousand metersTheir water can be highly acidic (as in some caldera lakes), nearly neutral, or highly alkaline (as in soda lakes). Lakes can be low in nutrients (oligotrophic), moderately enriched (mesotrophic), or highly enriched (eutrophic).

The different types of lakes are described below:

Glacial Lakes: By far the most important agents in the formation of lakes are the catastrophic effects of glacial ice movements that occurred 10,000 to 12,000 years ago. Gigantic sheets of ice and snow are created in climates where snow falls but does not melt. Although these glaciers did eventually melt, ten percent of the earth is presently covered with glaciers. Some of these glaciers can still be seen in the mountainous areas of the world.

As a glacier moves back and forth across the land, scraping off the tops of hills and bluffs and taking rocks with it, lakes are formed. The material picked up by the glacier is later dropped off at other sites. This back and forth and stop and go movement of the glaciers permanently alters the landscape. This movement creates several important landforms. When the glacier stops, it leaves behind piles of rocks and materials that it carried over time, called moraines. This dams up rivers and smaller streams to form lakes. Sometimes, huge blocks of ice are broken off and covered by sand and gravel. When the ice melts, the sand and gravel cave in, leaving a large hole behind. These kettles may form large marshes or lakes. As the large mass of ice melts, rivers form beneath the glaciers.

Solution Lakes: Lakes can form when underground deposits of soluble rocks are dissolved by water running through the area, making a depression in the ground. Rock formations made of sodium chloride (salt), or calcium carbonate (limestone), are most likely to be dissolved by acidic waters. Once the groundwater has dissolved the rocks below the surface, the top of the land caves in, usually forming a round-shaped lake, called a solution lake. Typically, the depressions are deep enough to extend below the groundwater table and are permanently filled with water. Solution lakes are common in Michigan, Indiana, Kentucky and particularly in Florida.

Oxbow Lakes: The flow of water from rivers has a great deal of energy and erosive strength that may create lake basins. As a river winds over the earth’s surface, a greater amount of erosion occurs on the outer river bend, where the flow of water is the fastest. Materials carried by the river are deposited on the inner portion of the bend, where currents are reduced. As time passes, erosion continues and more materials are left off until the U-shaped meander of the river closes in. The main course of the river cuts a new channel to the inner end of the meander. Oxbow lakes are usually shaped like the letter C.

Man-made or Animal-made Lakes: Many small lakes in India have been formed by the activities of the dam construction. Sticks, aquatic plants and mud are used to build dams across small streams to form an impoundment of the water. These ponds are usually very shallow and are rich in nutrients and plant life. Humans have constructed artificial lakes (reservoirs) to supply drinking water to the public, to provide power, to aid in navigation, to provide flood control and for recreational purposes. These reservoirs are usually well engineered by humans to hold back a certain quantity of water with the use of dams.

Volcanic Lakes: Sometimes, disastrous events associated with volcanic activity form lake basins. The formation of volcanic lakes can occur in different ways. As volcanic material, including magma, is discharged out of the volcano, empty depressions or cavities are formed within the volcano. Some of these depressions cannot drain and become sealed holes on top of the volcano. Rainfall and runoff eventually fill the depression with water and a new lake is formed.

Lakes that form in the craters of volcanoes, or crater lakes, are more common in areas that are subject to volcanic activity. Lakes formed by the caving in of a roof of a partially empty magmatic chamber are termed calderas. One of the most spectacular lakes formed in this way is Crater Lake in Oregon. Volcanic basins, like Crater Lake, are usually very round in shape.

Lava flows from volcanic activity can also form lakes. The surface lava cools, and becomes solid, while the inside of the lava flow remains hot enough to continue moving. Eventually, the surface of the hardened lava collapses, forming a depression. These depressions eventually fill with water to form smaller lakes. Lava streams also flow into existing river valleys and solidify into a dam. This solid mass of rock backs up the river water into a new lake.

Landslide lakes: Large quantities of materials that fall from the sides of steep valleys into the floors of stream valleys can cause dams that create new lakes. Such landslides usually occur as a result of abnormal meteorological events, such as excessive rains acting on an unstable slope. Landslide dams may be a result of rockfalls, mudflows or even ice-slides. Lakes that are formed by landslides are usually only temporary because they may be susceptible to erosion by the flow of the river or stream. If the dam is very large, the lake may become permanent.

Tectonic lakes: Tectonic basins are depressions formed by the movements of the earth’s crust deep underground. The major types of tectonic basins are formed from faulting. A depression forms when a weak section of the earth’s crust separates, resulting in an earthquake. Rainfall and groundwater may collect in this depression, forming a lake. This type of basin is referred to as a graben and is the mode of origin of a large number of the most spectacular relic lakes in the world containing a vast number of native plant and animal species. The deepest lake in the world, Lake Baikal in Siberia, was formed from tectonic activity.



Last Updated on Wednesday, 23 April 2014 07:13

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