Showing posts with label Lakes. Show all posts
Showing posts with label Lakes. Show all posts
Wednesday, October 28, 2009
MARSHES AND BOGS
MARSHES AND BOGS A bog is an area of wet, spongy ground, consistj.ng of decomposing moss and other vegetation, on the surface of a shallow pond or lake. Marshes and swamps are poorly drained, low-lying tracts of land that possess distinct flora. These are places where water stands at or close to the ground surface over a broad area. Some emerge by shifting of river channels on flood plains, while others emerge from the sea. Rushes, reeds and certain mosses are characteristic of marshland. A marsh may be drained to provide agricultural land as has occurred in the Fens of East Anglia.
SOME IMPORTANT LAKES IN INDIA
SOME IMPORTANT LAKES IN INDIA
Some of the important lakes in India are-Oal and Wular lakes in Jammu and Kashmir; Chllka lake in Orissa;Ohebar, Sambhar and Pushkar lakes in Rajasthan; Bhimtal, Satta or Satta I and Roop Kund in Uttarakhand; BhoJ wetland in Bhopal (M.P.); Chandratal, KhaJjlar, Nake, Renuka lakes in Himachal Pradesh; Pulicat lake on the Coromandel Coast on the Andhra Pradesh-Tamil Nadu border; Chembarambakkam. Kalivell and Veeranam lakes in Tamil Nadu; Hussain Sagar Himayat Sagar and Osman Sagar lakes in Hyderabad and Kolleru in Andhra Pradesh; Loktal (also called Floating Lake) in northeast India; Khecheopalrl and Tsongmo lakes in Sikkim; Vembanad, Vembanattu and Veeranpuzha lakes in Kerala.
Some of the important lakes in India are-Oal and Wular lakes in Jammu and Kashmir; Chllka lake in Orissa;Ohebar, Sambhar and Pushkar lakes in Rajasthan; Bhimtal, Satta or Satta I and Roop Kund in Uttarakhand; BhoJ wetland in Bhopal (M.P.); Chandratal, KhaJjlar, Nake, Renuka lakes in Himachal Pradesh; Pulicat lake on the Coromandel Coast on the Andhra Pradesh-Tamil Nadu border; Chembarambakkam. Kalivell and Veeranam lakes in Tamil Nadu; Hussain Sagar Himayat Sagar and Osman Sagar lakes in Hyderabad and Kolleru in Andhra Pradesh; Loktal (also called Floating Lake) in northeast India; Khecheopalrl and Tsongmo lakes in Sikkim; Vembanad, Vembanattu and Veeranpuzha lakes in Kerala.
LAKES
A lake is a body of water that lies in a hollow on. the earth's surface and is entirely surrounded by land. It is unconnected with the sea except by rivers. In arid and semiarid areas lakes may have no outlet to the sea and form the focus of an area of inland drainage. As a result the water of the lake becomes increasingly saline. Some inland seas are actually large lakes, e.g:, the Caspian Sea, Dead Sea artd Aral Sea.
CLASSIFICATION OF LAKES Though most lakes have been formed by the action of glaciers and icesheets, others have been formed by rivers, marine and wind action, by earth movement and vulcanicity, and a few lakes are also man-made. Some basic categories may be considered.
(i) Lakes produced by earth movements These are lakes formed by tectonic forces. They may be formed in two ways. (a) By crustal warping. These occupy basin-like depressions e.g., Caspian Sea, Lake Victoria (Africa), Lake Eyre (Australia). Lake Titicaca (Peru/Bolivia) is the highest tectonic lake in the world. (b) By faulting. These occur in rift valleys, e.g., Lake Nyasa (East Africa), the Dead Sea and Loch Ness (Scotland). These lakes are usually long, narrow and deep.
(ii) Lakes formed by erosion They may be of two types.
a) Both valley glaciers and ice sheets gouge out hollows and troughs on earth surface which later get filled with water to form lakes. These may be cirque lakes, forming in arm-chain-like depressions, also called tarns, found in mountain regions, or they may be trough lakes which occupy long hollows excavated in valley bottoms, also called ribbon lakes. They may also be rock basin lakes, formed by ice-scouring action of ice sheets resulting in formation of shallow hollows, as in Canada and Finland.
(b) Wind-eroded lakes: In the extensive depressions which are created by wind-erosion in the arid regions, if excavation is carried out below the water table, a lake may develop; e.g., the Qattara Depression in Egypt. Oases formed out of aquifers are more permanent lakes. Some desert lakes-palaya, for example-dry up because of excessive evaporation.
(iii) Lakes produced by deposition These may be of the following kinds. (a) River deposits: Ox-bow lakes _are cutoffs of mature rivers, made in flood plains, which eventually get separated from the river. They are common in lower valleys of the Mississippi. Deposits of alluvium in deltas may isolate a distributary, thus producing a delta lake, e.g., Etang de Vaccares in the Rhone Delta.
(b) Lakes produced by glacial deposits: Moraine-dammed lakes are caused by the deposition of terminal moraine across a valley, e.g., in the Lake District (England). Lake Grade (Italy) was formed like this. Depressions in boulder clay result in lake formation, such as the lakes in Northern Ireland.
(c) Marine deposits can form lakes: They are called Haffs. These lakes have been formed by sand bars extending along a coast and cutting off indentations in the coast, thus producing lagoons. These are found in southern coast of Baltic Sea and along Les Landes coast of south-west France.
(iv) Lakes produced by vulcanicity
(a) Crater and caldera lakes: Craters are formed when the top of a volcano gets blown off in a violent eruption. A caldera is formed if a crater gets enlarged by subsidence. Examples are Crater Lake in Oregon (USA), Lake Toba in north Sumatra and Lake Knebel in Iceland.
(b) Lava-blocked lakes: River valleys get blocked by lava to form a lake; the Sea of Galilee was formed by lava-flow blocking Jordan valley.
(c) Lavasubsidence lakes: These are caused by depressions caused by collapse of the lava crust, e.g., Myvatn, in Iceland.
(v) Other Types
(a) Solution lakes: Some rocks are dissolved and removed by rain water. This produces underground caverns. Limestone caverns collapse to expose lakes which are usually long and narrow, e.g., Lac de Chailexon in Jura Mountain. Sometimes, solution, aided by subsidence, produces large depressions called polje. Rock salt has been removed by solution in Cheshire (England) and the depressions have formed containing lakes, called 'flashes'.
(b) Barrier lakes: These are temporary lakes formed by ice, lava, moraine damming a valley, or damming by landslides, avalanches or screes.
(c) Beaver lakes: These are created by some animals like beavers which build dams across the streams to form lakes, e.g., Beaver lake in Yellow Stone National Park (USA).
(d) Mining ponds: These are caused by open cast mining, e.g., by tin mining in West Malaysia. (e) Man-made lakes: These are artificial lakes made by building dams across rivers.
Importance and Use Lakes play an important role. They are used for communication as natural routes; for hydro-electric power development; for regulating the flow of rivers; as a source for fishery; for water storage; for providing irrigating water. They also moderate the climate.
CLASSIFICATION OF LAKES Though most lakes have been formed by the action of glaciers and icesheets, others have been formed by rivers, marine and wind action, by earth movement and vulcanicity, and a few lakes are also man-made. Some basic categories may be considered.
(i) Lakes produced by earth movements These are lakes formed by tectonic forces. They may be formed in two ways. (a) By crustal warping. These occupy basin-like depressions e.g., Caspian Sea, Lake Victoria (Africa), Lake Eyre (Australia). Lake Titicaca (Peru/Bolivia) is the highest tectonic lake in the world. (b) By faulting. These occur in rift valleys, e.g., Lake Nyasa (East Africa), the Dead Sea and Loch Ness (Scotland). These lakes are usually long, narrow and deep.
(ii) Lakes formed by erosion They may be of two types.
a) Both valley glaciers and ice sheets gouge out hollows and troughs on earth surface which later get filled with water to form lakes. These may be cirque lakes, forming in arm-chain-like depressions, also called tarns, found in mountain regions, or they may be trough lakes which occupy long hollows excavated in valley bottoms, also called ribbon lakes. They may also be rock basin lakes, formed by ice-scouring action of ice sheets resulting in formation of shallow hollows, as in Canada and Finland.
(b) Wind-eroded lakes: In the extensive depressions which are created by wind-erosion in the arid regions, if excavation is carried out below the water table, a lake may develop; e.g., the Qattara Depression in Egypt. Oases formed out of aquifers are more permanent lakes. Some desert lakes-palaya, for example-dry up because of excessive evaporation.
(iii) Lakes produced by deposition These may be of the following kinds. (a) River deposits: Ox-bow lakes _are cutoffs of mature rivers, made in flood plains, which eventually get separated from the river. They are common in lower valleys of the Mississippi. Deposits of alluvium in deltas may isolate a distributary, thus producing a delta lake, e.g., Etang de Vaccares in the Rhone Delta.
(b) Lakes produced by glacial deposits: Moraine-dammed lakes are caused by the deposition of terminal moraine across a valley, e.g., in the Lake District (England). Lake Grade (Italy) was formed like this. Depressions in boulder clay result in lake formation, such as the lakes in Northern Ireland.
(c) Marine deposits can form lakes: They are called Haffs. These lakes have been formed by sand bars extending along a coast and cutting off indentations in the coast, thus producing lagoons. These are found in southern coast of Baltic Sea and along Les Landes coast of south-west France.
(iv) Lakes produced by vulcanicity
(a) Crater and caldera lakes: Craters are formed when the top of a volcano gets blown off in a violent eruption. A caldera is formed if a crater gets enlarged by subsidence. Examples are Crater Lake in Oregon (USA), Lake Toba in north Sumatra and Lake Knebel in Iceland.
(b) Lava-blocked lakes: River valleys get blocked by lava to form a lake; the Sea of Galilee was formed by lava-flow blocking Jordan valley.
(c) Lavasubsidence lakes: These are caused by depressions caused by collapse of the lava crust, e.g., Myvatn, in Iceland.
(v) Other Types
(a) Solution lakes: Some rocks are dissolved and removed by rain water. This produces underground caverns. Limestone caverns collapse to expose lakes which are usually long and narrow, e.g., Lac de Chailexon in Jura Mountain. Sometimes, solution, aided by subsidence, produces large depressions called polje. Rock salt has been removed by solution in Cheshire (England) and the depressions have formed containing lakes, called 'flashes'.
(b) Barrier lakes: These are temporary lakes formed by ice, lava, moraine damming a valley, or damming by landslides, avalanches or screes.
(c) Beaver lakes: These are created by some animals like beavers which build dams across the streams to form lakes, e.g., Beaver lake in Yellow Stone National Park (USA).
(d) Mining ponds: These are caused by open cast mining, e.g., by tin mining in West Malaysia. (e) Man-made lakes: These are artificial lakes made by building dams across rivers.
Importance and Use Lakes play an important role. They are used for communication as natural routes; for hydro-electric power development; for regulating the flow of rivers; as a source for fishery; for water storage; for providing irrigating water. They also moderate the climate.
PRINCIPAL RIVER SYSTEMS OF THE WORLD
1. Nile (Africa): The longest river, 6690 km; White Nile originates from Lake Albert in Uganda and Blue Nile from Ethiopia; the two join together at Khartoum in Sudan to form River Nile. After flowing through Egypt (the river's longest course), it falls into the Mediterranean Sea near Alexandria.
2. Amazon (South America): Originates from the Andes Mountain in Peru; tributaries come from Bolivia, Ecuador and Venezuela; the river flows mainly through Brazil and falls into the Atlantic Ocean.
3. Yangtze Kiang (Asia): Rises in north-east Tibet; and flows mainly through China, draining into the East China Sea.
4. Mississippi-Missouri (North America): Mississippi rises in Lake Itasca in Minnesota state of USA; Missouri joins it at Saint Louis; together, they flow into the Gulf of Mexico at New Orleans.
5. Mackenzie (North America): Rising in Great Slave Lake, it flows through Canada to Mackenzie Bay in the Arctic Ocean.
6. Mekong (Asia): Rises in Tibet, enters China through which it flows and later forms, for some distance, the borders between Thailand and Laos and falls into the South China Sea.
7. Niger (Africa): Rising near Sierra Leone, it crosses Niger and flows mainly through Nigeria and enters the Atlantic Ocean at the Gulf of Guinea.
8. Murray-Darling (Australia): Murray rises in the Australian Alps; Darling, its biggest tributary, joins it in the state of New South Wales. Both empty into the Indian Ocean at Encounter Bay.
9. Volga (Europe): Rises in Valdai Plateau north-west of Moscow, Russia, and enters the Caspian Sea at Astrakhan.
10. Danube (Europe): Rises near Baden in Germany, flows through Austria, Hungary, Czechoslovakia and Yugoslavia, crosses Romania and enters the Black Sea.
2. Amazon (South America): Originates from the Andes Mountain in Peru; tributaries come from Bolivia, Ecuador and Venezuela; the river flows mainly through Brazil and falls into the Atlantic Ocean.
3. Yangtze Kiang (Asia): Rises in north-east Tibet; and flows mainly through China, draining into the East China Sea.
4. Mississippi-Missouri (North America): Mississippi rises in Lake Itasca in Minnesota state of USA; Missouri joins it at Saint Louis; together, they flow into the Gulf of Mexico at New Orleans.
5. Mackenzie (North America): Rising in Great Slave Lake, it flows through Canada to Mackenzie Bay in the Arctic Ocean.
6. Mekong (Asia): Rises in Tibet, enters China through which it flows and later forms, for some distance, the borders between Thailand and Laos and falls into the South China Sea.
7. Niger (Africa): Rising near Sierra Leone, it crosses Niger and flows mainly through Nigeria and enters the Atlantic Ocean at the Gulf of Guinea.
8. Murray-Darling (Australia): Murray rises in the Australian Alps; Darling, its biggest tributary, joins it in the state of New South Wales. Both empty into the Indian Ocean at Encounter Bay.
9. Volga (Europe): Rises in Valdai Plateau north-west of Moscow, Russia, and enters the Caspian Sea at Astrakhan.
10. Danube (Europe): Rises near Baden in Germany, flows through Austria, Hungary, Czechoslovakia and Yugoslavia, crosses Romania and enters the Black Sea.
Rivers and Lakes
A river is a large stream of fresh water flowing downhill within a channel to enter another river or a lake or sea. All rivers ultimately receive their water from precipitation, though this relation is not a very simple one. The flow of a river depends upon three main factors: the amount and intensity of rainfall, governed by climatic factors; the permeability of the surface on which it is flowing; and the morphological properties of the drainage basin. The nature of the vegetation cover also plays an important role. When water flows in a stream, it is subject to two basic forces: gravity, aimed downstream and causing the flow; and frictional resistance between the water and the river bed. The effect of friction ensures an uneven velocity of water flow in the river. Thus, water near the centre moves the fastest while it is slow near the banks.
PARTS OF RIVER
The place at which the river begins to flow is called its source. It may be in the melt waters of a glacier, e.g., the Rhone (France), or in a lake, e.g., the Nile (Africa), or in a spring, e.g., the Thames (England), or in a region of steady rainfall, e.g., the Zaire (Africa). The place where the river ends is called a river's mouth. It is usually in the sea, e.g., the Indus (Arabian Sea) and the Amazon (Atlantic), although it may be in a lake, e.g., the Volga (Caspian), or in a salt swamp, e.g., the Chari River (Lake Chad) and the Tarim River (Lap Nor).
A mature river has three sections: (i) the upper course representing the stage of youth of a river, called the torrent stage; (ii) the middle course, representing the state of maturing called the valley stage, and (Hi) the lower course, representing the stage of old age and called the plain stage. In the stage of youth, the river flows turbulently in a narrow steep-sided valley whose floor is broken by (a) 'potholes' or circular depressions in the river bed, caused by pebbles,
(b) waterfalls, occurring where the bed of the river becomes suddenly steepened. Some deep and narrow valleys having very steep sides are called gorges. These are formed where a waterfall retreats upstream. The head waters of the Ganga have cut deep gorges in the Himalayas. The Indus Gorge in Kashmir is 5180 metres. Canyons are large gorges, formed in dry regions where large rivers are actively eroding vertically. A canyon is a deep valley with steep, near vertical sides. River Colorado has cut a gorg~ 1.6 km (1 mile) deep and 480 km (300 miles) long into the Colorado plateau (USA).
As the valley widens, meanders are formed. A meander is a loop. in the course of a river channel. Water flows in corkscrew manner, causing erosion on the concave bank and deposition on the convex bank.
In the mature stage form the flood plains-low lying land composed of deposits of sediment (alluvium). Meanders migrating downstream cause widening of the valley. Ox-bow lakes are produced by cut-offs in a meander during floods.
Reaching old age, the river deposits its load into the sea or lake into which it flows. The deposited load sometimes collects in the river mouth, where it builds up into a low-lying swampy plain called a delta. The river divide~ into several channels due to the depositions at its mouth, called distributaries. Arcuate deltas are formed by coarse sediments like gravel and sand and are triangular in shape, having many distributaries, e.g., in Rivers Ganga, Indus, Nile, Niger, Hwang-Ho. Bird's foot deltas are composed of very fine sediments, having few distributaries with clearly defined channels, like the Mississippi delta. An estuarine delta develops in the mouth of a submerged river, e.g., deltas of Elbe (Germany) and Ob (Russia).
A river does three types of work: it erodes, and most erosion takes place in the upper course; it transports: a process dominant in the middle course; and it deposits: depositional process is dominant in the lower course of the river. A river's ability to work, Le., to erode and transport material, depends upon its energy. Potential energy is provided by weight and the elevation of water. This is converted into downflow by gravity and thus into kinetic energy. However, about 95 per cent of this energy is lost due to frictional resistance.
PARTS OF RIVER
The place at which the river begins to flow is called its source. It may be in the melt waters of a glacier, e.g., the Rhone (France), or in a lake, e.g., the Nile (Africa), or in a spring, e.g., the Thames (England), or in a region of steady rainfall, e.g., the Zaire (Africa). The place where the river ends is called a river's mouth. It is usually in the sea, e.g., the Indus (Arabian Sea) and the Amazon (Atlantic), although it may be in a lake, e.g., the Volga (Caspian), or in a salt swamp, e.g., the Chari River (Lake Chad) and the Tarim River (Lap Nor).
A mature river has three sections: (i) the upper course representing the stage of youth of a river, called the torrent stage; (ii) the middle course, representing the state of maturing called the valley stage, and (Hi) the lower course, representing the stage of old age and called the plain stage. In the stage of youth, the river flows turbulently in a narrow steep-sided valley whose floor is broken by (a) 'potholes' or circular depressions in the river bed, caused by pebbles,
(b) waterfalls, occurring where the bed of the river becomes suddenly steepened. Some deep and narrow valleys having very steep sides are called gorges. These are formed where a waterfall retreats upstream. The head waters of the Ganga have cut deep gorges in the Himalayas. The Indus Gorge in Kashmir is 5180 metres. Canyons are large gorges, formed in dry regions where large rivers are actively eroding vertically. A canyon is a deep valley with steep, near vertical sides. River Colorado has cut a gorg~ 1.6 km (1 mile) deep and 480 km (300 miles) long into the Colorado plateau (USA).
As the valley widens, meanders are formed. A meander is a loop. in the course of a river channel. Water flows in corkscrew manner, causing erosion on the concave bank and deposition on the convex bank.
In the mature stage form the flood plains-low lying land composed of deposits of sediment (alluvium). Meanders migrating downstream cause widening of the valley. Ox-bow lakes are produced by cut-offs in a meander during floods.
Reaching old age, the river deposits its load into the sea or lake into which it flows. The deposited load sometimes collects in the river mouth, where it builds up into a low-lying swampy plain called a delta. The river divide~ into several channels due to the depositions at its mouth, called distributaries. Arcuate deltas are formed by coarse sediments like gravel and sand and are triangular in shape, having many distributaries, e.g., in Rivers Ganga, Indus, Nile, Niger, Hwang-Ho. Bird's foot deltas are composed of very fine sediments, having few distributaries with clearly defined channels, like the Mississippi delta. An estuarine delta develops in the mouth of a submerged river, e.g., deltas of Elbe (Germany) and Ob (Russia).
A river does three types of work: it erodes, and most erosion takes place in the upper course; it transports: a process dominant in the middle course; and it deposits: depositional process is dominant in the lower course of the river. A river's ability to work, Le., to erode and transport material, depends upon its energy. Potential energy is provided by weight and the elevation of water. This is converted into downflow by gravity and thus into kinetic energy. However, about 95 per cent of this energy is lost due to frictional resistance.
Subscribe to:
Posts (Atom)
