Physical Geography (Part-11): Islands & Coral Reefs

Islands and Coral Reefs

An island is a piece of land surrounded on all sides by water. It may occur individually or in a group, in open oceans or seas. Smaller ones of only local significance are found even in lakes and rivers. 

All Islands may be grouped under the following types:

1.) Continental Islands: These islands were formerly part of the mainland and are now detached from the continent. They may be separated by a shallow lagoon or a deep channel. Their separation could be due to subsidence of some part of the land or to a rise in sea level so that the lowland links are submerged by the sea. Their former connection with the neighbouring mainland can be traced from the similar physical structure, flora and fauna that exist on both sides of the channel. Over time, modification by men and other natural forces may give rise to different surface features. But even then, the basic structural features will remain the same. Continental islands may appear as:

• Individual Island: These lie just outside the continent, very much associated with the characteristics features of the mainland of which they were once part. Example- Newfoundland, separated from the mainland by the Strait of Belle Isle, Madagascar, by the Mozambique Channel, Ceylon by the Palk Strait, Tasmania by the Bass Strait and Formosa by the Formosa Strait.

• Archipelagoes or Island groups: These comprise groups of islands of varying sizes and shapes. Eg. the British Isles, the Balearic Islands of the Mediterranean and also those of the Aegean Sea.

• Festoons or Island arc: The islands form an archipelago in the shape of a loop around the edge of the mainland, marking the continuation of mountain ranges that can be traced in the continent. Eg. the East Indies, the Aleutian Island, Ryukyu Islands, Kurile Islands and other arcs of the Pacific coasts. 

2.) Oceanic Islands: These islands are normally small and are located in the midst of oceans. They have no connection with the mainland which may be hundreds or thousands of miles away. They have a flora and fauna unrelated to those of the continents. The Galapagos Islands have many unique species of animals. Due to their remoteness from the major trading centres of the world, most of the oceanic islands are very sparsely populated. Some of them provide usefully stops for aeroplanes and ocean streams that ply between continents across vast stretches of water.

Generally, oceanic islands fall into one of the following groups:

• Volcanic Islands: Many of the islands in the oceans are in the fact the topmost part of the cones of volcanoes that rise from the ocean bed. Most of them are extinct, but there are also some active ones. The best known volcanic peak of the Pacific Ocean is Muana Loa in Hawaii, which is 13,680 feet above sea level. Mauna Loa is found to have been built up from the water surface! Other volcanic islands have emerged from the submarine ridges of the oceans. The volcanic islands are scattered in most of the earth's oceans. In the Pacific Ocean, they occur in several groups such as Hawaii, the Galapagos Island and the South Sea islands. In the Atlantic are the Azores, Ascension, St. Helena, Madeira and the Canary Islands. Those of the Indian Ocean are Mauritius and Reunion. In the Antarctic Ocean are the South Sandwich Islands, Bouvet Island and many others.

• Coral Island: The coral islands are very much lower and emerge just above the water surface. These islands, built up by coral animals of various species, are found both near the shores of the mainland and in the midst of oceans. Coral islands include the Marshall Islands, Gilbert and Ellice Islands of the Pacific, Bermuda in the Atlantic and the Laccadives and Maldives of the Indian Ocean.

Coral Reefs:

In tropical seas, many kinds of coral animals and marine organisms such as coral polyps, calcareous algae, shell-forming creatures and lime-secreting plants live in large colonies. Though they are very tiny creatures, their ability to secrete calcium carbonate within tiny cells has given rise to a particular type of marine landform. They exist in numerous species of my forms, colours and shapes. Under favourable conditions, they grow in great profusion just below the water level. Taking coral animals as a whole, the polyps are the most abundant and also the most important. Each polyp resides in a tiny cup of coral and helps to form coral reefs. When they die, their limy skeletons are connected to coastline limestones. There are also non-reef-building species such as the 'precious corals' of the pacific ocean and the 'red coral' of the Mediterranean which may survive in the colder and even the deeper waters. As a rule, they thrive well only in the warmer tropical seas.

The reef-building corals survive best under the following conditions:

• The water temperature must not fall below 68° F (20°C). This virtually limits the areal distribution of coral s to the tropical, and subtropical zones. Again they will not flourish where there are cold currents because of the upwelling of the cold water from the depths that cools the warm surface water. This explains why coral reefs are generally absent on the western coasts of continents. On the other hand of the warming effect of the warm currents eg. the Gulf stream, means that corals are found to the north of the West Indies in the Atlantic Ocean. The pacific and the Indian oceans, however, have the most numerous coral reefs.

• The depth of the water should not exceed 30 fathoms or 180 feet, because beyond this depth sunlight is too faint for photosynthesis to take place. This is essential for the survival of the microscopic algae, on which the coral polyps depend. The shallow water of fewer than 100 feet is ideal. But there should always be plenty of water as polyps cannot survive for too long out of water.

• The water should be saltish and free from sediment. Corals, therefore, survive best in the moving ocean water well away from the silty coasts or muddy mouths of streams. The corals are best developed on the seaward side of the reef, where constantly moving waves, tides and currents maintain an abundant supply of clear, oxygenated water. They also bring an adequate supply of food in the form of microscopic organisms.

Types of Coral Reefs:

There are three (3) main types of coral reefs:

1.) Fringing reefs: A fringing reef is a coralline platform lying close to the shore extending outwards from the mainland. It is sometimes separated from the shore by a shallow lagoon. It is widest when fringing a protruding headland but completely absent when facing the mouth of the stream. The outer edge grows rapidly because of the splashing waves that continuously renew the supply of fresh food. The reefs may be about a mile wide, lying just above the level of low water and sloping steeply downwards on the seaward side to a depth of about 100 feet.

2.) Barrier reef: A barrier reef is separated from the coast by a much wider and deeper channel or lagoon. The reef is partially submerged. where it lies above the water level and sand can accumulate on it, a little vegetation is possible. The barrier reefs have narrow gaps at several places to allow the water from the enclosed lagoon to return to the open ocean. Such gaps are very useful for shipping and provide the only entrances for ships to enter or leave the lagoon. Eg. the Great Barrier reef off the coast of Queensland (Australia). It is 1,200 miles long, separated from the coast by a channel 100 miles wide in places and over 200 feet deep.

3.) Atolls: Atolls are similar to barrier reefs except that they are circular in shape, enclosing a shallow lagoon without any land in the centre. The encircling ring is usually broken in a few places to allow the free flow of water. On the inside of the reefs, sand and limestone debris collect and palm trees like coconuts may grow. Such palm trees thrive well in the brackish water of the lagoon. The nuts fall into the water and are distributed widely by floating from one coral island to another. The calm waters are useful for fishing and canoeing. Some of the large atolls eg. Suvadiva (Maldives), west of Ceylon, have a lagoon over 40 miles across. A number of them provide essential air bases for trans-Pacific aircraft. 

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Physical Geography (Part-7): Arid and Desert Landforms

Arid and Desert Landforms

About a fifth of the world's land is made up of deserts, some rocky other stony, and the rest sandy. Deserts that are absolutely barren and where nothing grows at all are rare and they are better known as 'true deserts'.

On the World's Map almost all the deserts are confined within the 15° to 30° parallels of latitude N and S of the equator. They lie in the trade wind belt on the western parts of the continents where Trade Winds are off-shore. They are bathed by cold currents which produce a 'desiccating effect' so that moisture is not easily condensed into precipitation. Dryness or aridity is the keynote. Such deserts are tropical hot deserts or 'Trade Wind deserts'. Example: Great Sahara deserts, Arabian, Iranian, and Thar deserts, Kalahari, Namib, and Atacama deserts, the Great Australian deserts, and the desert of the south-west USA and northern Mexico. In the continental interiors of the mid-latitudes, the deserts such as Gobi and Turkestan are characterized by extremes of temperatures. 

The work of winds and water in eroding elevated uplands, transporting the worn-off materials, and depositing them elsewhere, has given rise to five distinct kinds of a desert landscape.

• Himalayan or Rocky Desert: This consists of large stretches of bare rocks, swept clear of sand and dust by the wind. The exposed rocks are thoroughly smoothed and polished. The region is bare and sterile. The best known rocky deserts are those of the Sahara deserts eg. Hamada el Homra (Libya), which covers almost 20,000 square miles.

• Reg or Stony Desert: This is composed of extensive sheets of angular pebbles and gravels which the winds are not able to blow off. Such stony deserts are much more accessible than the sandy deserts, and large herds of camels are kept there. In Libya and Egypt, the term serir is used; elsewhere in Africa, stony deserts are called reg.

• Erg or Sandy Desert: This is a sea of sand that typifies the popular ideas of desert scenery. Winds deposit vast stretches of undulating sand-dunes in the heart of the deserts. The intricate patterns of the ripples on the dune surfaces indicate the direction of the winds. The Calanscio Sand Sea (Libya) is characteristic of a sandy desert. In Turkestan, sandy deserts are also known as koum.

• Badlands: The term 'badlands' was first given to an arid area in South Dakota (USA), where the hills were badly eroded by occasionally rainstorms into gullies and ravines. The extent of water action on hill slopes and rock surfaces was so great that the entire region was abandoned by the inhabitants. Deserts with similar features are now referred to as badlands. Eg. the Painted Desert (Arizona), which lies southeast of the Grand Canyon of Colorado River.

• Mountain Deserts: Some deserts are found on highlands such as plateaux and mountain ranges. Erosion has dissected the desert highlands into harsh, serrated outlines of chaotic peaks and craggy ranges. Their steep slopes are cut by wadis (steep-sided, often dry, valleys) and the action of frost has craved out sharp, irregular edges. Eg. In the Sahara Desert, the Ahaggar Mountains, and the Tibesti Mountains.

The Mechanism of Arid Erosion:

Arid landforms are the results of many combined factors, one creating upon the other. Insufficient rainfall (often less than 5 inches) coming at most irregular periods, coupled with very high temperatures (87° F is the average) and a rapid rate of evaporation, are the chief causes of aridity. Sub-aerial denudation through the processes of weathering (mechanical and chemical), wind action, and the work of water have combined to produce a desert landscape that is varied and distinctive.

Weathering: This is the most potent factor in reducing rocks to sand in arid regions. Even though the amount of rain that falls in the desert is small, some manage to penetrate into the rocks and sets up chemical reactions in the various minerals. Intense heating during the day and rapid cooling at night by radiation set up stresses in the already weakened rocks so that they eventually crack. As heat penetrates rocks slowly when the outer surface of rocks remains quite cool. The heating of the rocks causes the outer surface to expand and so prise itself off from the interior rocks so that it peels off in successive very thin layers. As the onion-peeling process of mechanical weathering is called exfoliation. Angular rock debris is found in abundance as screes at the foot of upstanding rocks. Similarly, when water gets into the cracks and joints of rocks and the temperature at night suddenly drops to below freezing point, the water freezes and therefore expands by 10% of its volume. Successive freezing will prise off fragments of rock that accumulate as screes. These rock fragments become the 'teeth' or tools of wind erosion.

Action of winds in deserts: The wind though not the most effective agent of erosion, transportation, and deposition is more efficient in arid than in humid regions. Since there is little vegetation or moisture to bind the loose surface materials, the effects of wind erosion are almost unrestrained.

Wind erosion is carried out in the following ways:

• Deflation: This involves the lifting and blowing away of loose materials from the ground. Such unconsolidated sands and pebbles may be carried in the air or rolled along the ground depending on the grain size. The finer dust and sands may be removed miles away from their place of origin, and be deposited even outside the desert margins. Deflation results in the lowering of the land surface to form large depressions called deflation hollows. The Qattara Depression (Sahara Desert) lies almost 450 feet below sea level.

• Abrasion: The sand-blasting of rock surfaces by winds that hurl sand particles against them is called abrasion. The impact of such blasting results in rock surfaces being scratched, polished and worn away. Abrasion is most effective at or near the base of rocks, where the amount of material the wind can carry is greatest. A great variety of desert features are produced by abrasion.

• Attrition: When wind-borne particles roll against one another in a collision they were each other away so that their sizes are greatly reduced and grains are rounded into millet seed sand. This process is called attrition.

Landforms of Wind Erosion in Deserts:

• Rock pedestal or Mushroom rocks: The sand-blasting effect of winds against any projecting rock masses wears back the softer layers so that an irregular edge is formed on the alternate bands of hard and soft rocks. Grooves and hollows are cut in the rock surfaces, carving them into fantastic and grotesque-looking pillars called rock pedestals. Such rock pillars will be further eroded near their bases where the friction is greatest. This process of undercutting produces rocks of mushroom shape called mushroom rocks or gour in the Sahara.

• Zeugen: These are tabular masses that have a layer of soft rocks lying beneath a surface layer of more resistant rocks. The sculpting effects of wind abrasion wear them into a weird-looking ridge and furrow landscape. Mechanical weathering initiates their formation by opening up joints of the surface rocks. Wind abrasion further eats into the underlying softer layer so that deep furrows are developed. The hard rock then stands above the furrows as ridges or zeugen and many even overhang. Such tabular blocks of zeugen may stand 10 to 100 feet above sunken furrows. Continuous abrasion by wind gradually lowers the zeugen and widens the furrows. 

• Yardangs: Quite similar to the 'ridge and furrow' landscape of zeugen are steep-sided yardangs. Instead of lying in horizontal strata upon one another, the hard and soft rocks of yardangs are vertical bands and are aligned in the direction of the prevailing winds. Wind abrasion excavated the bands of softer rocks into long, narrow corridors, separating the steep-sided overhanging rides of hard rocks, called yardangs. They are commonly found in the Atacama Desert (Chile), but the more spectacular ones with yardangs rising to 25-50 feet are best developed in the interior deserts of Central Asia.

• Mesas and Buttes: Mesa= table (in Spanish). It is a flat, table-like landmass with a very resistant horizontal top layer and very steep sides. The hard stratum on the surface resists denudation by both wind and water, and thus protects the underlying layers of rocks from being eroded away. Mesas may be formed in canyons regions eg. Arizona, or on fault blocks eg. the Table Mountain (Cape Town, South Africa). Continued denudation through the ages may reduce mesas in the area so that they become isolated flat-topped hills called buttes. Many of them in arid countries are separated by deep gorges or canyons.

• Inselbergs: Inselbergs= island mountain (in German). They have isolated residual hills rising abruptly from the level ground. They are characterized by their very steep slopes and rather rounded tops. They are often composed of granite or gneiss and are probably the relics of an original plateau that has been almost entirely eroded away. Inselbergs are typical of many deserts and semi-arid landscapes in old age eg. Nothern Nigeria, Western Australia, and the Kalahari Desert.

• Ventifacts or Dreikanter: These are pebbles faceted by sand-blasting. They are shaped and thoroughly polished by wind abrasion to shapes resembling Brazil nuts. Rock fragments, mechanically weathered from mountains and upstanding rocks are moved by wind and smoothed on the windward side. If the wind direction changes another facet is developed. Such rocks have characteristics of flat facets with sharp edges. Amongst the ventifacts, those with three wind-faceted surfaces are called dreikanter. These wind-faceted pebbles from the desert pavement a smooth, mosaic-like region, closely covered by the numerous rock fragments and pebbles.

• Deflation hollows: Wind lower the ground by blowing away the unconsolidated materials, and small depressions may form. Similarly, minor faulting can also initiate depressions and the eddying action of on-coming winds will wear off the weaker rocks until the water table is reached. Water then seeps out forming oases or swamps, in the deflation hollows or depressions. The Faiyum Depression in Egypt lies 130 feet below sea level. Large areas in the western USA, stripped of their natural vegetation for farming, were completely deflated when strong winds, moved materials as dust-storms, laying waste crops and creating what is now known as the Great Dust Bowl. In a dust storm, winds may lift dust hundreds of feet high and carry it thousands of miles away.

Landforms of Wind Deposition in Deserts:

Materials eroded and transported by winds must come to rest somewhere. The finest dust travels enormous distances in the air and may be moved completely out of the desert. It has been estimated that some dust grains travel as far as 2,300 miles of dust before they are finally deposited on land or sea. The dust from the Sahara Desert is sometimes blown across the Mediterranean to falls as blood rains in Italy or on the glaciers of Switzerland. Dust that has accumulated over past centuries to a depth of several hundred feet!

The following are some of the major features of wind deposition:

1.) Dunes: Dunes are, in fact, hills of sand formed by the accumulation of sand and shaped by the movement of winds. They may be active or live dunes, constantly on the move, or inactive fixed dunes, rooted with vegetation. Dunes are most well represented in the erg desert where a sea is redeposited into a variety of features. Because of their great contrast in shape, size, and alignment, they have been given a long list of fanciful names, such as attached dune or head dune, tail dune, advanced dune, lateral dune, wake dune, star dune, pyramidal dune, sword dune, parabolic blow-out dune, hairpin dune, smoking dune, and transverse dune. Various types of common dunes:

• Barchans: These are crescentic or moon-shaped dunes that occur individually or in groups. They are live dunes that advance steadily before winds that come from a particular prevailing direction. They are most prevalent in the desert of Turkestan and in the Sahara. Barchans are initiated probably by a chance accumulation of sand at an obstacle, such as a patch of grass or a heap of rocks. They occur transversely to the wind so that their horns thin out and become lower in the direction of the wind due to the reduced frictional retardation of the winds around the edges. The windward side is convex and gently sloping while the leeward side, being sheltered, is concave and steep. The crest of the sand dune moves forward as more sand is accumulated by the prevailing wind. The sand is driven up the windward side and, on reaching the crest, slips down the leeward side so that the dune advances. The rate of advancement varies from 25 feet a year for the high dunes measuring up to 100 feet high, to 50 feet a year, for the lower dunes which may be only a dozen feet high. The migration of the barchans may be a threat to desert life for they may encroach on an oasis burying palm trees or houses. Long rooted trees and grasses are therefore planted to halt the advances of the dunes thus preventing areas of fertile land from being devastated. Under the action of winds, barchans take a chaotic changing pattern. Several barchans may coalesce into a line of irregular ridges, ever-changing with the direction of the winds. Ergs or sandy deserts are thus most difficult to cross.

• Seifs or longitudinal dunes: Seif= sword (in Arabic). They are long, narrow ridges of sand, often over a hundred miles long lying parallel to the direction of the prevailing winds. The high, serrated ridges may attain a height of over 200 feet. The Crestline of the seif rises and falls in alternate peaks and saddles in regular successions like the teeth of a monstrous saw. The dominant winds blow straight along the corridor between the lines of dunes so that they are swept clear of sand and remain smooth. The eddies that are set up blow towards the sides of the corridor, and, having less power, drop the sand to form the dunes. In this manner, the prevailing winds increase the length of the dunes into tapering linear ridges while the occasional crosswinds tend to increase their height and width. Extensive seif dunes are found in the Sahara Desert, south of the Qattara Depression, the Thar Desert, and the West Australian Desert.

2.) Loess: The fine dust blown beyond the desert limits is deposited on neighboring lands as loess. It is a yellow, friable material and is usually very fertile. Loss is in fact, fine loam, rich in lime, very coherent, and extremely porous. Water sinks in readily so that the surface is always dry. Streams have cut deep valleys through a loess region soon sink and their walls rise steeply. The most expensive deposit of loess is found in northwest China in the loess plateau of the Hwang-Ho basin. It is estimated to cover an area of 250,000 square miles, and the deposits have accumulated to a depth of 200 to 500 feet! In China, such yellowish wind-borne dust from the Gobi Desert is called 'Hwangtu-the yellow earth'! But the original term loess actually comes from a village in Alsace, France. Similar deposits also occur in some parts of Germany, France and Belgium, and are locally called Limon. They are also wind-borne but were blown from material deposited at the edge of ice sheets during the Ice Ages. In part of the Mid-West, USA loess was derived from the ice sheets which covered northern North America and is termed adobe.

Landforms due to Water Action in Deserts:

Few deserts in the world are entire without rain or water. The annual precipitation may be small, 5 to 10 inches, and comes in irregular showers. But thunderstorms do occur and the rain falls in torrential down porous, producing devastating effects. A single rainstorm may bring several inches of rain within a few hours, drowning people who camp in dry desert streams and flooding mud-baked houses in the oases. A desert has little vegetation to protect the surface soil, large quantities of rock wastes are transported in sudden ranging torrents or flash-floods. Loose gravel, sand and fine dust are swept down the hillsides. They cut deep gullies and ravines forming badland topography. Subsequent down porous widen and deepen the gullies when they wash down more soft rocks from the surface. There is so much material in the flash floods that the flow becomes liquid mud. When the masses of debris are deposited at the foot of the hill or the mouth of the valley, an alluvial cone or fan or 'dry delta' is formed, over which the temporary stream discharges through several channels, depositing are subjected to rapid evaporation by the hot sun and downward percolation of water into the porous ground, and soon dry up leaving mounds of debris.

Apart from gullies, there are many larger dry channels or valleys. These are deepened by vertical corrosion by raging torrents during the occasional cloudburst. These are wadis and are dry for most of the time. Some desert streams are fed by the melting snow of the distant mountains outside the deserts and rivers flow as exotic streams. The water carves out steep walls, which rise abruptly from the stream bed. In Algeria, such gorges are termed chebka.

In arid and semi-arid areas the outflowing streams from the upland regions are both short and intermittent. They drain into the lower depressions so that drainage is almost entirely internal. Sometimes water collected in a depression or a desert basin does not completely disappear by evaporation or seepage, and a temporary lake is formed. Such lakes contain a high percentage of salts, because of high evaporation, and are glistening white when they dry up. The lakes and the alluvial plains formed by them are called playas, salinas or salars in the United States, Mexico, and shotts in northern Africa. The floor of the depression is made up of two features, the bajada and the pediment. The bajada is a depositional feature made up of alluvial material laid down by the intermittent streams. The pediment is an erosional plain formed at the base of the surrounding mountain scarps.

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Physical Geography (Part-8): Lime Stone & Chalk Landforms

Limestone and Chalk Land-Forms

Limestone and chalks are sedimentary rocks of organic origin derived from the accumulation of corals and shells in the sea.

In its pure state, limestone is made up of calcite or calcium carbonate, but where magnesium is also present it is termed dolomite. Chalk is a very pure form of limestone, white and rather soft. Limestone is soluble in rainwater, which, with carbon dioxide from the air, forms a weak acid. A region with a large stretch of limestone, therefore, possesses a very distinct type of topography. It is then, termed a karst region, a name derived from the Karst district of Yugoslavia where such topography is particularly well developed.

Characteristics features of a Karst Region:

Karst region has a bleak landscape, occasionally broken by precipitous slopes. There is a general absence of drainage as most of the surface water has gone underground. Streams raising of the other rocks only flow over limestone for a short distance and then disappear underground. For the greater part of their course, they cut their way along the joints and fissures of the rock wearing out a system of underground channels. The surface valleys are therefore dry. When the water penetrates to the base of the limestone and meets non-porous rocks it re-emerges onto the surface as a spring or resurgence.

Limestones are well jointed and it is through these joints and cracks that rainwater finds its way into the underlying rock. Progressive widening by solution enlarges these cracks into trenches and a most intriguing feature called limestone pavement is developed. The enlarged joints are called grikes and the isolated, rectangular blocks are termed clints. The limestone pavements may have been formed beneath the soil and are now exposed by the removal of the soil cover.

On the surface of the limestones are numerous swallow holes, which are small depressions carved out by solution where rainwater sinks into the limestone at a point of weakness. They are also known as sinkholes. Example: Gaping Ghyll in Yorkshire. These holes grow in size through continuous solvent action.

Once the water has sunk into the limestone it etches out caverns and passages along joints or bedding planes. When the roof of an underground tunnel collapses, a precipitous limestone gorge such as the Cheddar Gorge is formed. Where several swallow holes coalesce a larger hollow is formed and is called a doline. Several Dolina may merge as a result of subsidence to form a larger depression called an uvala. Some of them are miles across, containing much clayey soil from the limestones, weathered after their subsidence.

In Yugoslavia, some very large depressions called polje may be as large as hundred square miles but these are partly due to faulting. During the rainy season, parts of the floor that are at or near the water table may become temporary lakes, but the drier areas are fertile and may support large villages.

Where subterranean streams descend through swallow holes to underground passages, the region may be honeycombed with caves and caverns, some containing ponds and lakes. The most spectacular underground features that adorn the limestone caves are stalactites, stalagmites, and pillars.

• Stalactites: These are the sharp, slender, downward-growing pinnacles that hang from the cave roofs. The water carries calcium in the solution and when this lime-charged water evaporates, it leaves behind the solidified crystalline calcium carbonate.

• Stalagmites: As moisture drips from the roof it trickles down the stalactite and drops to the floor where calcium is deposited to form stalagmites. They are shorter, flatter, and more rounded.

• Pillar: Over a long period, the stalactite hanging from the floor forms a pillar. Such features are commonly seen in any well-developed limestone cave eg. Batu caves, Kuala Lampur, Mammoth caves, Kentucky and Carlsbad cave, New Mexico, in the USA, and Postojna caves, Yugoslavia.

The major Limestone Regions of the World:

• The most characteristics stretch of limestone occurs in north-west Yugoslavia.

• Other regions include the Causses district of southern France, the Pennines of Britain, Yorkshire, and Derbyshire in particular, the Kentucky region of United States, the Yucatan Peninsula of Mexico, the Cockpit Country of Jamaica, and the limestone hills of Perlis.

Human activities of Karts Regions:

Karts regions are often barren and at best carry a thin layer of soil. The porosity of the rocks and the absence of surface drainage make vegetative growth difficult, so that limestone can usually support only poor and short turf, some sheep grazing is possible. Limestone vegetation in tropical regions, however, is luxuriant because of the heavy rainfall all year round. Settlement is scattered and the population is often sparse. The only mineral of importance is lead which occurs in veins in association with limestone. Besides this, good-quality limestones are often used as building material or quarried for the cement industry.

In West Malaysia, the limestone outcrops of the Kledang range and the Main range are quarried for the Pan-Malaysian and Tasek Cement Works.

Chalk:

The landforms of chalk are rather different from those of other limestones. There is little or no surface drainage and valleys that once contained rivers are now dry. These are often called coombes. The chalk forms low rounded hills in southern and southern eastern England, where they are called downs, and in Northern France. 

The chalk is covered with short turf, and in places with woodland, and is used for pasture and sometimes for arable farming. Because of the friable nature of the rock, swallow-holes and underground cave networks do not generally develop.

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Jharkhand Geography: River Valley Projects- JPSC/ JSSC

River Valley Projects :

The water resources department (WRD, Jharkhand) is making efforts to expand the land under irrigation by implementing large, medium, and small irrigation projects for storage and conservation of all water resources in the state after making a proper estimation of their availability.

In addition to this work is in progress for infrastructure creation for the conservation of enrichment flotation and optimal use of underground water resources. 

Several different projects launched by the water resources department (WRD) have been able to create irrigation capacity for a total of 9.198 lakh hectares of agricultural land, which is 37.40% of the total land out of that about 24.59 lakh hectares is good for irrigation. 

The multipurpose river valley project also has been implemented in the state. There are the following objects for River Valley Projects:

• Augmentation of the irrigation area;
• Power generation & industrial development;
• Fishery;
• Flood Control;
• Cattle feed;
• Production of drinking water;
• Recreational activities.

Major Irrigation Projects

The most significant major multipurpose projects in the state are following:

Damodar Valley river project (Damodar Valley Corporation)

• The first multipurpose River Valley multipurpose project in independent India
• Established in: 1948 on the lines of the Tennessee river project in the United States of America.
• Objective: The main objectives of this project are power generation & irrigation.
• The project provides irrigation to eight lakh hectares of land and generates 1200 megawatts (MW) of power.
• Eight dams listed below have been built under this project.

River	Dams
Barakar	Tilaiya, Maithon, Balpahari
Damodar	Panchet, Aiyar (Tenughat), Bermo
Bokaro	Konar, Garga

Other Important Projects:

Subarnarekha Multipurpose Project (Chandil Dam):

• Launched: 1980- 83 and construction for its first stage was completed by 2003.
• Objectives: planned for irrigation, hydro-power generation, and water supply.
• This is an interstate project launched jointly by Jharkhand, West Bengal, and Odhisa.
• Chandil Dam & Galudih Barrage across River Suvarnarekha;
• Icha Dam & Galudih Barrage, Ganjia Barrage across River Kharkai have been constructed under this project.
• Hundu Fall is being used for the generation of 120-megawatt (MW) power under this river project.

Konar Irrigation Project:

• 1955: Konar dam is the second of the 4-multipurpose dams included in the first phase of Damodar Valley Corporation (DVC), built-in Hazaribagh, and inaugurated by India's First Prime Minister Pt. Jawaharlal Nehru, for irrigation purposes.
• 1978: Then Bihar Governor Jagannath Kaushal had laid the foundation of the irrigation project in September 1978.
• This provides irrigation benefits to Hazaribagh, Giridih, and Bokaro district.

Ajay Barrage project:

• This project is located in Deoghar and Jamtara district.
• This Barrage has been constructed under this project across the Ajay river near Sikatia village in Sarath block of Deoghar district.
• This 110 km long Canal has been constructed under the same, which provides irrigation in Jamtara, Nala, and Kundahit blocks.

Gumani Barrage Project:

• Started- 1977.
• This Barrage has been constructed under the Gumani river near Pettarkhassa village of Barhait block in Sahibganj district.
• This provides irrigation in the Barhait, Patan, Barharwa, Littipara, and Hiranpur blocks of Sahibganj and Pakur districts.

Punasi Reservoir Project:

• Under this scheme, a dam is being constructed near Punasi village in the Deoghar district.
• This scheme will provide irrigation benefits to Chanan, Katoria,  Saraiyahat, Mohanpur, and Sarvan blocks in the Deoghar district.

Amanat Barrage Project:

• The Barrage under this project is being constructed across the Amarnath river in the Panki block (Medininagar) of Palamu District.
• This project will provide irrigation benefits to Panki, Manatu, and Patan blocks in Palamu District.
• After this completion, the project will provide irrigation facilities to 25,000 hectares of farmland.

North Koel Reservoir:

• The project is being constructed on the north Koel river near Kutku village in Garhwa District.
• Under this project, a composite dam and barrage are being constructed across the Koel river.
• The 109 km long right main canal from the barrage will provide irrigation facilities to Palamu District whereas the 11.81 km long left main canal will serve the Garhwa district.
• The project also includes the generation of 24 megawatts (MW) of power.
• The National Park is also located in the submersible area of the project.

Bateshwarsthan Ganga Pump Canal Scheme:

• This is an inter-state scheme of Jharkhand and Bihar states.
• Under this scheme, water will be lifted from the Ganges and released in a canal.
• The scheme will provide irrigation of Mahatma and Mahagama blocks of Godda district.

Upper Shankh Reservoir:

• Under this scheme, a dam is being constructed across the Sankh River near Tangal village in the Dumri block of Gumla district.

Sonua Reservoir Scheme:

• The scheme involves the construction of a dam across the Sanjay River near Parsua village under the Sonua block of West Singhbhum district.

Panchkhero Reservoir Scheme:

• This is under construction across the Panchkhero River.
• Rajdhanwar block of Giridih district and Markhaccho block of Koderma district are covered under the scheme.
• This scheme will provide irrigation to 2548 hectares of Kharif crops and 537 hectares of Rabi crops.

Sukri Reservoir Scheme:

• The scheme is under construction across the Sukri river near Banjari village in the Kisko block of Lohardaga district.
• This will provide irrigation to 440 hectares of land in the Kisko block.

Bhairwa Reservoir Scheme:

• Under this scheme, a dam is being constructed across the Bhairwa River near Sonai village in the Gola block of Ramgarh district.
• This scheme will provide irrigation to 3643 hectares of Kharif crops and 1214 hectares of Rabi crops.

Ram Rekha Reservoirs:

• This dam is being constructed across Utayal Nala in the Simdega district near Kairbaira village.
• This will provide irrigation to 4405 hectares of land in the Simdega block of the Simdega district.

Batane Reservoir Scheme:

• Under this scheme, a dam is being constructed across the Batani river near Dhabudih village in Palamu District.
• This is an inter-state project of Bihar and Jharkhand.
• This will provide irrigation to 2360 hectares of land in the Palamu District.

Much more irrigation scheme listed below are proposed:

• Tiliaya Irrigation Scheme: Tilaiya- Dhadhar Irrigation project, Jayanagar, Koderma.
• Domni Nala Irrigation Scheme: Kharaundhi, Garhwa.
• Budhai Irrigation Project: Madhupur, Deoghar.
• Radhu Irrigation Project: Silli, Ranchi.
• Daharbati Irrigation Scheme: Kisko, Lohardaga.

In addition to the irrigation scheme above mentioned, a 'Water Resolution Campaign' has been initiated by the State Government in the year 2015-16 based on the policies of the Government of India for the development of water resources. 

• Under this campaign, 48 villages in 24 districts (two villages for every district) have been selected as Jal-Grams.
• A comprehensive Integrated Water Security Plan (CIWSP) has been formulated to make these villages self-sufficient in all kinds of water needs.
• The Government of India is providing 50% of the fund required for the Command area of the Kanchi Weir Scheme in the Ranchi district. This scheme will provide irrigation facilities to 3 blocks- Bundu, Tamar, Sonahatu in Ranchi district, and Arki block in Khunti district. 
• The Government of India has accorded approval for the development of the command area of the Mayurakshi Reservoir Scheme in the Dumka district.

Irrigation Project of Jharkhand:

Kind of Project	Name of the Project	River	District/ State
Central Multipurpose Scheme	Damodar River Valley (DVC) Project	Damodar	Jharkhand, West Bengal
Comprehensive Irrigation Scheme under AIBP	Subarnarekha Multipurpose Project	Subarnarekha, Kharkai	Jharkhand, West Bengal, Odisha
Comprehensive Irrigation Project of the State	Konar Irrigation Project	Konar	Hazaribagh
	Ajay Barrage Project	Ajay	Deoghar, Jamtara
	Gumani Barrage Project	Gumani	Sahibganj
	Punasi Reservoir Project	Ajay	Deoghar
	Amanat Barrage Project	Amanat	Palamu
	North Koel Reservoir Project	North Koel	Garhwa, Palamu, Latehar
	Bateshwarsthan Ganga Pump Canal Project	Ganga	Godda
Medium Irrigation Scheme	Upper Sankh Reservoir Scheme	Sankh	Gumla
	Sonua Reservoir Scheme	Sanjay	West Singhbhum
	Panchkhero Reservoir Scheme	Panchkhero	Giridih, Koderma
	Sukri Reservoir Scheme	Sukri	Lohardaga
	Bhairwa Reservoir Scheme	Bhairwa	Ramgarh
	Ramrekha Reservoir Scheme	Utayal Nala	Simdega
	Kesho Reservoir Scheme	Sakri	Koderma
	Batane Reservoir Scheme	Batane	Palamu
	Raisa Reservoir Scheme	Raisa	Ranchi
	Tajna Reservoir Scheme	Tajna	Khunti
	Surangi Reservoir Scheme	Surangi Nala	Tamar (Ranchi)
	Nakti Reservoir Scheme	Nakti Nala	Bandagaon (West Singhbhum)
	Shuru Nakti Reservoir Scheme	Shuru Nala	West Singhbum, Saraikela-Kharsawan

  

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