LAKES

  • A lake is a water body of considerable size, localized in a basin, that is surrounded by land apart from a river or other outlet that serves to feed or drain the lake.
  • Lakes are found on land and are not part of the ocean system, therefore are distinct from lagoons, and are also larger and has more depth than ponds.
  • Natural lakes are commonly found in mountainous areas, rift zones, and areas with ongoing glaciation.
  • Most lakes have at least one natural outflow in the form of a river or stream, which maintain a lake’s average level by allowing the drainage of excess water
  • Although a few lakes do not have a natural outflow and lose water solely by evaporation or underground seepage. They are termed endorheic lakes.
  • The majority of lakes on Earth are fresh water lakes, and most lie in the Northern Hemisphere at higher latitudes. Canada, Finland and Siberia contain most of the fresh water lakes.

 

CLASSIFICATION OF LAKES

A) Temporary lakes

  • Lakes may exist temporarily filling up the small depressions of undulating ground after a heavy shower.
  • In this kind of lakes, the Evaporation > Precipitation.
  • Example: Small lakes of deserts.

B) Permanent lakes

  • In this kind of lakes, Evaporation < Precipitation.
  • These lakes are deep and receives more water than their evaporation.
  • Example: Great Lakes of North America, East African Rift Lakes.

C) Fresh water lakes

  • Most of the lakes in the world are fresh-water lakes fed by rivers and with out-flowing streams e.g. Great Lakes of North America.

D) Saline lakes

  • Salt lakes (saline lakes) can form where there is no natural outlet or where the water evaporates rapidly and the drainage surface of the water table has a higher-than-normal salt content.
  • Because of the intense evaporation,these lakes are saline.
  • Examples of salt lakes include Great Salt Lake, the Aral Seaand the Dead Sea.
  • the Dead Sea has a salinity (salt content) of 250 parts per thousand, and the Great Salt Lake of Utah, U.S.A. has a salinity of 220 parts per thousand.
  • Playas or salt lakes, are a common feature of deserts.

E) Lakes Formed by Earth Movement

Tectonic lakes

  • Due to the warping (simple deformation), subsidence,bending and fracturing of the earth’s crust, tectonic depressions occur.
  • Such depressions give rise to lakes of enormous sizes and depths.
  • Examples – Lake Titicaca, and the Caspian Sea.

 

 

Rift valley lakes

  • A rift valley is formed when two blocks of earth move apart letting the ‘in between’ block slide downwards. Or, it’s a sunken land between two parallel faults.
  • Rift valleys are deep, narrow and elongated. Hence the lakes formed along rift valleys have same features.
  • Water collects in troughs (Valley in the rift) and their floors are often below sea level.
  • The best-known example is the East African Rift Valleywhich runs through Zambia, Malawi, Tanzania, Kenya and Ethiopia, and extends along the Red Sea to Israel and Jordan over a total distance of 3,000 miles.
  • It includes such lakes as Lakes TanganyikaMalawi, Rudolf, Edward, Albert, as well as the Dead Sea1,286 feet below mean sea level, the world’s lowest lake.

 

 

F) Lakes Formed by Glaciation

Cirque lakes or tarns

  • Cirque is a hollow basin cut into a mountain ridge. It has steep sided slope on three sides, an open end on one side and a flat bottom.
  • When the ice melts, the cirque may develop into a tarn lake.

 

 

Rock-hollow lakes

  • The advance and retreat of glaciers can scrape depressions in the surface where water accumulates; such lakes are common in Scandinavia, Patagonia, Siberia and Canada.
  • These are formed by ice-scouring (eroding) when ice sheets scoop out (dig) hollows on the surface.
  • Such lakes of glacial origin are abundant in Finland – Land of Lakes. It is said that there are over 35,000 glacial lakes in Finland.

Lakes due to morainic damming of valleys

  • Valley glaciers often deposit morainic debris across a valley so that lakes are formed when water accumulates behind the barrier.

G) Lakes Formed by Volcanic Activity

Crater and caldera lakes

  • During a volcanic explosion the top of the cone may be blown off leaving behind a natural hollow called a crater.
  • This may be enlarged by subsidence into a caldera.
  • In dormant or extinct volcanoes, rain falls straight into the crater or caldera which has no superficial outlet and forms a crater or caldera lake.
  • Examples: Lonar in Maharashtra and Krakatao in Indonesia.

H) Lakes Formed by Erosion

Karst lakes

  • The solvent action of rain-water on limestone carves out solution hollows. When these become clogged with debris lakes may form in them.
  • The collapse of limestone roofs of underground caverns may result in the exposure of long, narrow- lakes that were once underground.

Wind-deflated lakes

  • The winds in deserts creates hollows. These may reach ground water which seeps out forming small, shallow lakes. Excessive evaporation causes these to become salt lakes and playas. Example: Great Basin of Utah, U.S.A.

I) Lakes Formed by Deposition

Lakes due to river deposits

  • Ox-bow lake, e.g. those that occur on the flood-plains of Lower Mississippi, Lower Ganges etc.

Lakes due to Marine deposits

  • Also called Lagoons.
  • Example: Lake Chilka

Lakes due to damming of water

  • Lakes formed by these processes are also known as barrier lakes. Landslides, avalanches may block valleys so that rivers are dammed. Such lakes are short-lived.
  • Lakes that are formed in Shiwaliks (Outer Himalayas). Dehradun (all Duns) were lakes formed a few centuries ago.

Man-made lakes

  • Besides the natural lakes, man has now created artificial lakes by erecting a concrete dam across a river valley so that the river water can be kept back to form reservoirs.
  • Example: Lake Mead above the Hoover Dam on the Colorado River, U.S.A.
  • Man’s mining activities, e.g. tin mining in West Malaysia, have created numerous lakes. Inland fish culture has necessitated the creation of many fishing-lakes.

 

LAKES AND HUMANS

A) Means of communication

  • Large lakes like the Great Lakes of North America provide a cheap and convenient form of transport for heavy and bulky goods such as coal, iron, machinery, grains and timber.
  • The Great Lakes-St. Lawrence waterwayspenetrate more than 1,700 miles into the interior. They are thus used as the chief arteries of commerce.
  • In countries where they are found in abundance, such as Finland, Canada, U.S.A., Sweden and the East African states, lakes are used as inland waterways.

B) Economic and industrial development

  • The Great Lakes-St. Lawrence waterways were responsible for the development of the interior wheat farms and lakeside automobile and steel industries.

C) Water storage

  • Kolleru lake in Andhra Pradesh.

D) Hydro-electric power generation

  • Artificial lakes like Hirakud.

E) Agricultural purposes

  • Many dams are built across artificial lakes.
  • Bhakra Nangal Dam. Its reservoir, known as the “Gobind Sagar Lake”and Hirakud Dam (Madhya Pradesh) on the Mahanadi in India.

F) Regulating river flows

  • Hoover Dam on the River Coloradoand the Bhakra and Nangal Dams on the Sutlej in India.
  • The Hirakud dam was originally conceived as a flood control measure.

G) Moderation of climate

  • Lakes moderate the extreme temperatures of the surrounding regions.

H) Source of food

  • Many large lakes have significant supplies of proteinsas freshwater fish. Sturgeon is commercially caught in the Caspian Sea, salmon and sea trout in the Great Lakes.

I) Source of minerals

  • Salt lakes provide valuable rock salts. As in Dead Sea, the highly saline water is being evaporated and produces common salt. Borax is mined in the salt lakes of the Mojave Desert.

J) Tourist attraction and health resorts

  • Lake Chilka, Leh, Dead Sea etc.

 

IMPORTANT LAKES ON EARTH

A) World

 

B) India

There is no need to remember – which is the largest/ longest/deepest lakes. Please locate these lakes on the map and remember the country of their location in a few important cases.

C) Lake Baikal – Deepest and largest lake in the world.

  • Located in Siberia, Russia.
  • The deepest lake in the world[1,637 metres deep) and also the world’s largest lake by volume.

D) Lake Tanganyika – Longest Lake

  • The longest lake in the world. (660 kilometres long) and also the second largest by volume.
  • It is the second deepest lake in the world, after lake Baikal.

E) World’s Highest and Lowest Lakes

  • The world’s highest lake, if size is not a criterion, may be the crater lake of Ojos del Salado, at 6,390 metres. It is in Andes.
  • The highest large lake in the world is the Pumoyong Tso (Pumuoyong Tso), in the Tibet Autonomous Region of China. (5 kms above sea level)
  • The world’s highest commercially navigable lake is Lake Titicaca in Peru and Bolivia border at 3.8 kms above sea level. It is also the largest lake in South America.
  • The world’s lowest lake is the Dead Sea, bordering Israel and Jordan at 418 metres below sea level. It is also one of the lakes with highest salt concentration.

F) The Largest Lakes (surface area) by Continent

  • Australia – Lake Eyre(Salt Lake)
  • Africa – Lake Victoria, also the third-largest freshwater lake on Earth. It is one of the Great Lakes of Africa.
  • Antarctica – Lake Vostok(subglacial)
  • Asia – Lake Baikal(if the Caspian Sea is considered a lake, it is the largest in Eurasia, but is divided between the two geographic continents)
  • Europe – Lake Ladoga, followed by Lake Onega, both located in north western Russia.
  • North America – Lake Superior.
  • South America – Lake Titicaca, which is also the highest navigable body of water on Earth at 3,812 metres above sea level. The much larger Lake Maracaibo is a contiguous body of water with the sea, so it is ignored.

G) Great Lakes

  • Great Lakes of North America are a series of interconnected freshwater lakes which connect to the Atlantic Ocean through the Saint Lawrence river-Seaway.
  • Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario[in the order of west to east].
  • Lake Superior is the largest continental lake in the world by area, and Lake Michigan is the largest lake that is entirely within one country.

 

 

H) Dead Sea( important for prelims)

  • Also called the Salt Sea.
  • Lake bordering Jordan to the east, and Palestine and Israel to the west.
  • It Earth’s lowest elevation on land.

 

 

I) Aral Sea

  • It is a lake lying between Kazakhstan in the north and Uzbekistan, in the south.
  • Aral Sea has been steadily shrinking since the 1960s after the rivers that fed it were diverted for the Soviet irrigation projects.

J) African Great Lakes

  • Series of lakes constituting the part of the Rift Valley lakes in and around the East African Rift.
  • They include Lake Victoria, the second largest fresh water lake in the world, and Lake Tanganyika, the world’s second largest in volume as well as the second deepest.

 

 

K) Largest Lakes by Surface Area

  1. Lake Superior – North America
  2. Lake Victoria – Africa
  3. Lake Huron – North America
  4. Lake Michigan – North America

L) Largest Lakes by Volume

  1. Baikal – Asia
  2. Tanganyika – Africa
  3. Superior – North America

M) Deepest Lakes in the World

  1. Lake Baikal – Asia
  2. Lake Tanganyika

 

CHANGES IN CRITICAL FEATURES

A) SHRINKING OF ARAL SEA: A MAN-MADE CRISIS

In the early 1900s, the Aral Sea was the fourth largest inland lake in the world.  By 2005, it had lost more than half of its surface area.

 

 

Causes

  • In 1918, policymakers from the former Soviet Union decided to divert fresh water from the Syr Darya and the Amu Darya for irrigation.
  • This was an essential part of their plans to increase cotton production1930s saw the construction of a system of irrigation canals. Crop production rose as irrigated areas in Uzbekistan and Turkmenistan increased.
  • But with its major inflows being diverted for irrigation, the Aral Sea began shrinking in the 1960s
  • Unfortunately, the much larger South Aral Sea is still shrinking. Uzbek leaders are unwilling to relinquish the primary water source for their cotton irrigation. Uzbekistan remains one of the world’s major cotton exporters, and thus the Amu Darya is still being diverted to irrigate the crops that sustain the lives of millions of people.

Consequences

  • The formerly thriving fishing industry collapsed as the freshwater influx declined and salinity increased, leading to the disappearance of thousands jobs linked to the Aral Sea fishery.
  • The dried up sea bed produced dust storms laden with chemicals and pesticides from the intensive agriculture occurring along the two rivers.
  • This in turn led to increased air and water pollution levels, and crop damage Thousands of people were forced to abandon their homes as their livelihoods dried up and their health was threatened.

B) Drying lakes crisis in India

 

 

  • Chennai, Bangalore, Bhopal and many other cities are facing water crisis because of drying of water bodies.
  • Chennai is one of several cities that is facing intense water shortage across the country. Tamil Nadu’s three reservoirs at lake Puzhal, Cholavaram and Chembarambakkam, which supply water to Chennai, have depleted dramatically because of following reasons: –
    • Large urban agglomerations utilize more water resource than the natural supply of the region, therefore these large cities with enormous population density can’t rely only on monsoons for replenishment of its lakes.
    • The poor and unplanned urban development and expansion of cities has blocked the natural ways for replenishment of lakes as water is not recycled and rainwater is not collected.
    • Ever increasing water scarcity in major cities will force thousands of MNCs to shift their base and will cause mass migration of professionals along with them.
  • Therefore, artificial measures for ground water recharge (rainwater harvesting or traditional baoli) must be taken by the civic agencies and the government
  • The Niti Aayog said last year that India was facing the worst long-term water crisis in its history as demand was outstripping supply.
  • Under the new government a new ministry named Jal shakti ministry was formed to formulate and implement policies and programmes for water supply and management.

 

VIDEOS TO WATCH FOR

Shrinking of the Dead Sea :

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