Lake – Classification of Lakes
Lakes are among the most varied features of the earth s surface. A lake is a large body of natural water accumulated in a depression. Lake basins are formed due to endogenous geological processes like tectonism and volcanism and exogenous activities like landslides, glaciation, solution, river and wind action.
Lake and Its Classification
They vary tremendously in size, shape, depth and mode of formation. The tiny ones are no bigger than ponds or pools, but the large ones are so extensive that they merit the name of seas, e.g. the Caspian Sea. The Caspian Sea is the largest lake regarding the area. The deepest lake in the Lake Baikal in Siberia.
Lakes occupy about 1.8 % of the earth s surface. About 280 000 cu.km of water exists on earth in the form of lakes. This is 0.19% of the total volume of water in the hydrosphere.
Advantages of lakes
- The major role played by lakes and reservoirs is the regulation of stream flow.
- Lakes provide water for drinking, factory, irrigation and generating hydel-power.
- Lakes are a good refuge for an enormous variety of flora and fauna.
- The lives of the people, in a region, are greatly influenced by the presence of a lake in that area.
- In some places, lakes are good sources for water supply for drinking.
- Lakes help in the growth of the fishing industry.
- The salt lakes yield common salt. For example, Sambar lake
- Lakes are helpful in controlling the weather and moderating local climate- Lakes cool the air in summer and warm it during winter. They also enhance the humidity.
- Lakes have an aesthetic appeal and are helpful in recreation; tourists are attracted due to lakes which have boating, swimming and a good landscape around.
- Lakes are used for navigation. For example the Great Lakes in North America
- Lakes also help in flood control as rivers passing through the lakes in their course seldom cause disastrous floods. The Wular lake and the Dal lake do not allow the Jhelum river to be flooded and due to lack of such lakes, the Brahmaputra is subjected to very great floods every year.
Lakes only a temporary feature?
Lakes are thought to be only a temporary feature of the earth s crust. Eventually, they will be eliminated by the dual process of draining and sitting up. In regions of unreliable rainfall, lakes dry up completely during the dry season. In the hot deserts, lakes disappear altogether by the combined processes of evaporation, percolation and outflow. Though the process of lake elimination may not be completed within our span of life, it takes place relatively quickly regarding geological time.
Classification of lakes
When there are a large number and variety of lakes, people tend to classify them. There are several types, kinds and categories of lakes in the world. Classification helps us to understand and visualize the relationships and helps us to communicate. The most common classification of lakes is based on the size or dimension of lakes, whether it is small, big or very large.
Lakes are mainly classified on the basis of:
a) Nature of Inflow-outflow
c) Trophic levels
a) Classification based on inflow-outflow
Temporary and Permanent Lakes
- Temporary Lakes -These lakes may exist temporarily by filling up small depressions of undulating grounds after a heavy shower. In such lakes rate of evaporation is much greater than the rate of recharge through precipitation. They are usually saline. They are subject to extreme fluctuations in water level. Example - Badhkal Lake, Faridabad
- Permanent lakes Permanent lakes carry more water than could ever be evaporated. These are very deep. They have some perennial source of inflow of water such as a glacier. They are usually freshwater lakes. Example Dal Lake
Freshwater and Salt lakes
- Freshwater lakes Most of the lakes in the world are freshwater lakes. They are usually found in low lying areas and are fed from streams, rivers and runoff from the surrounding area. e.g. Great Lakes of North America, Lake Baikal in Russia, Lake Wular and Loktak Lake in India.
- Salt Lakes Salt Lake is an inland body of water situated in an arid or semiarid region, having no outlet to the sea, and containing a high concentration of dissolved salt. These lakes exist in regions of low precipitation and intense evaporation. Because of intense evaporation, the concentration of salts increases in the water body, turning them saline. Playas or salt lakes are a common feature of deserts. Example - Great Salt Lake of Utah, USA, Dead Sea etc.
Great Lakes of North America
b) Classification based on origin or mode of formation
The following are the various ways in which lakes can be formed. Each of them is placed in a different category, though in a few cases the lake could have been formed by more than one single factor
1) Lakes formed by earth movement
- These lakes are formed by filling up with water in the tectonic depressions created due to warping, sagging, bending and fracturing of the earth s crust.
- Such depressions give rise to lakes of immense sizes and depths.
- Example Lake Titicaca, Chile, the Caspian Sea etc.
Rift Valley Lakes
- These lakes include some of the oldest, deepest and largest lakes around the globe.
- Due to faulting, a rift valley is formed by the sinking of the land between two parallel faults, deep, narrow and elongated in character.
- Water is collected in these troughs
- Often their floors are below sea level.
- The best example of this is the East African Rift Valley which includes such lakes as Lake Tanganyika and the Dead Sea etc.
2) Lakes formed by Volcanism
Crater and Caldera Lakes
- A natural hollow called a crater is formed by blowing off of the top of the cone during a volcanic explosion.
- Crater may be widened and enlarged by further subsidence into a caldera.
- These depressions are normally dry.
- In dormant or extinct volcanoes, due to rainfall straight into these depressions which have no superficial outlet, a crater or caldera lake is formed.
- Examples Lonar crater lake in Maharashtra, India, Crater Lake in Oregon, USA and Lake Toba in Sumatra etc.
- In volcanic regions, it is common to find a stream of lava that flows across a valley
- This stream of lava may occasionally become solidified and block the valley thus forming a lake basin
- This basin may get filled up due damming up of the river due to solidified lava
- Example The Sea of Galilee which is an inland lake was created due to blocking of the Jordan valley by lava flow
One more type of lake formed due to subsidence of a volcanic land surface is included under this type. Under this type of lake, the crust of a hollow lava flow may collapse. The subsidence leaves behind a wide and shallow depression in which the lake may form. E.g. Myvatn Lake of Iceland
3) Lakes formed by Glaciation
Cirque or tarn lakes
- Cirque, a common landform in glaciated mountains, is often found at the heads of glacial valleys.
- A glacier on its way down the valley leaves behind circular hollows.
- These circular hollows, in the heads of the valley up in the mountain, are called cirques.
- Cirques are very deep, long and wide troughs or basins.
- The head and sides of these cirques have very steep to vertically dropping high concave walls
- Often, a lake of water can be seen within the cirques after the disappearance of the glacier. Such lakes are referred to as the Cirque or tarn lakes
- They are also called as Ribbon lakes
- Example Red tarn in the English Lake District and Chandra Taal (Himachal Pradesh) in India
Cirque or Tarn Lakes
- These are depressions in the outwash plain left by melting of a large mass of stagnant ice
- They are irregular in shape, and also these lakes are not very large or deep
- Example Kettle-lakes of Orkney in Scotland
- These lakes are formed by ice scouring when valley glaciers or ice sheets scoop out hollows or depressions on the surface
- Such lakes are abundant in Finland
Two more types of a glacial lake are formed due to damming up of valleys by morainic debris deposited by valley glaciers and deposition of glacial drifts in glaciated lowlands .
4) Lakes formed by Erosion
- Karst lakes are formed in depressions, carved out by solvent action of rainwater on water-soluble rocks such as limestone, gypsum and dolomite.
- The collapse of limestone roofs of underground caves may result in the exposure of long, narrow lakes that were once underground.
- The shallow bed of these lakes is usually an insoluble layer of sediment so that water is impounded, resulting in the formation of lakes.
- Many karst lakes only exist periodically but return regularly after heavy rainfall.
- Example the Lac de Chaillexon in the Jura mountains
Otjikoto Karst Lake in Namibia
Wind deflated lakes
- These lakes are formed in arid regions and deserts
- The depressions are created in deserts due to deflating action of winds
- Groundwater may seep out in these depressions forming lakes
- Excessive evaporation causes these to become salt lakes and Playas
- Example Great Basin of Utah, USA
5) Lakes formed by deposition
- In large flood and delta plains, rivers rarely flow in straight courses. Loop-like channel patterns called meanders develop over flood and delta plains
- During a flood, a river may shorten its course by cutting across its meandering loops, leaving behind a horse-shoe shaped channel as an ox-bow lake
- Example Ox-bow lakes are a common phenomenon in the floodplains of Lower Mississippi, USA and Rio Grande (Mexico), Kanwar Lake Bird Sanctuary in Bihar, India is one of Asia's largest oxbow lakes.
Meandering or river and Formation of Oxbow Lakes
- These lakes are formed by landslides, avalanches and such other processes
- These processes cause damming up of the river by blocking the valleys
- These lakes are short lived as the large piles of loose fragments soon give way under the pressure of water. The sudden release of water from these lakes like this can also cause floods
- Example Lake Gormire in Yorkshire, blocked by a landslide
6) Man-made lakes
- Besides natural lakes, man has now created artificial lakes
- Artificial lakes are created by erecting a concrete dam across a river valley
- These dams help in creating a reservoir by impounding river water
- Guru Gobind Sagar Lake which supports the Bhakra Nangal Hydel Project is an example of an artificial lake in India
c) Classification based on trophic level
- Eutrophic lakes have very high levels of biological productivity.
- The excessive level of nutrients, especially phosphorus and nitrogen gives rise to an abundance of aquatic plants in these water bodies.
- Usually, the water body will be dominated either by aquatic plants or algae.
- Eutrophication might occur naturally or due to human impact on the environment.
- Some of Highly Eutrophicated Lake in India include Udaisagar Lake (Rajasthan) and Dal Lake (Kashmir)
A Eutrophic Lake
- Lakes with an intermediate level of productivity are called mesotrophic lakes.
- The nutrients level of these lakes in medium or moderate.
- They usually have clear water with submerged aquatic plants
- An oligotrophic lake is a lake with low primary productivity, as a result of low nutrient content.
- Algal production in these lakes is relatively low.
- Often, they have very clear waters, with high drinking water quality
- A paleolake is a lake that existed in the past when hydrological conditions were different.
- Often, Paleolakes are identified based on relict lacustrine landforms such as coastal landforms that form recognizable relict shorelines, referred to as paleo-shorelines.
- Paleolakes can also be recognized by characteristic sedimentary deposits that accumulated in them and any fossils that these sediments might contain.
- Evidence of prehistoric hydrological changes during the time of their existence can be found from the sedimentary deposits of paleo-shorelines and paleo-lakes.
Types of Paleolakes
Former Lake - A former lake is a lake which is no longer in existence. Former lakes include prehistoric lakes and permanently dried up lakes resulting from evaporation or human intervention. A good example of a former lake is Owens Lake in California, USA.
Shrunken Lake - A shrunken lake is a lake which has drastically decreased in size over geological time. A good example of a shrunken lake is Agassiz Lake, once covering much of central North America.