The lake basins are also filled and destroyed in the following ways

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Lakes, when viewed from geological point of view, are undoubtedly a temporary and ephemeral relief feature. Lake basins are ultimately filled and they disappear due to various factors.

According to Gilbert, “rivers are the mortal enemies of lakes.” In case the water level in a lake rises, there would be an increased outflow which leads to the deepening of the lake’s outlet.

In this way, the lake basin whose bottom is above the level of stream-cut valley is drained out. The lake basins are also filled and destroyed in the following ways:

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(i) Filling by sediments brought into the basins by streams

(ii) Filling by wave-action

(iii) Filling by wind-borne materials

(iv) Filling by organic accumulations

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(v) Filling by landsides and avalanches

(vi) Destruction by glaciers

(vii) Filling by delta growth.

(i) Filling by sediments:

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All streams flowing into lakes invariably bring with them sediments that are deposited on the floor of the basin. Slope wash from the borders of basins also aid in filling the basin by depositing sediments into them.

However, the amount of sediment varies in different streams. Besides, lake-bottom deposits are usually fine grained. They are formed in Lake Basin on or near the melting ice.

(ii) Filling by wave action:

Waves formed into lake water attack the shore of the lake and rock particles loosened by them are brought and deposited into the basin. Gradually the sediments fill the lake-basin.

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(iii) Filling by wind:

This process is more pronounced in arid regions where huge amount of dust and sand are blown into lakes. In some cases great quantities of volcanic dust have been blown into the lake basins.

(iv) Filling by organic accumulations:

The filling of lakes is aided by organism’s plant and animal organisms, using the mineral nutrients brought into the lake by streams, occupy the shore, build up communities on the floor, thus helping advance the shoreline farther into the lake area.

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As the lake becomes smaller and shallower, plants take root on its floor which gradually becomes marsh. It may also be converted into peat bogs and muskegs.

Muskeg, a Canadian Indian term for a Shagnum moss-covered bog in the sub-Arctic latitudes of Canada and Alaska. It is a region of marshy depressions. In addition, there are numerous shell-building animals and some plants that secrete lime or silica.

When these organisms die, their remains contribute a lot toward the deposits that fill the lake basin. Thousands of shallow lakes of glacial origin have been trans­formed into swamps in northern United States, Canada, and Europe.

(v) Filling by landslides and avalanches:

Filling of lakes by such processes is commonly seen in the mountains and plateaus. Such lakes as are situated at the foot of steep cliffs are filled with a lot of material brought in by landslides, mudflows and avalanches, etc.

Mountain lakes are generally characterized by huge boulders that fall into the lakes from nearby cliffs. Such materials ultimately destroy a lake.

(vi) Destruction by glaciers:

Filling of a lake by advancing glacier is completed by the removal of moraines. This is common in regions where glaciers are found.

(vii) Filling by delta growth:

Streams entering into a lake begin forming deltas by deposit­ing coarse and fine materials as sediments. As the deltas grow in size, the area of the lake begins to shrink. Ultimately the lake disappears and the lake basin is converted in a lacustrine plain.

(viii) Lake destruction by climatic change:

Lakes can also disappear when climate changes. If there is reduction in the amount of precipitation within a region or temperatures and net radiation increase, evaporation can exceed input and the lake will dry up.

Many former lakes of south western United States flourished in wet periods of glacial advance during the Pleistocene Age. But today the picture has altogether changed. Lakes have shrunk greatly or have disappeared completely under the present arid regime.

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