GC Leong Test: Arid Or Desert Landforms - UPSC MCQ

• Limestone and Chalk: Limestone and chalk are sedimentary rocks of organic origin derived from the accumulation of corals and shells in the sea. 

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  In its pure state, limestone is made up of calcite or calcium carbonate, but magnesium is also termed dolomite. Chalk is a very pure form of limestone, white, and rather soft. 

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  Limestone is soluble in rain-water, which forms a weak acid with carbon dioxide from the air. 

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  A region with a large stretch of limestone, therefore, possesses a very distinct type of topography.

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  It is then termed a karst region, a name derived from Yugoslavia's Karst district where such topography is particularly well developed.

• Characteristic Features of a Karst Region: Generally speaking, karst regions have a bleak landscape, occasionally broken by precipitous slopes. 

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  There is a general absence of surface drainage as most of the surface water has gone underground. Streams rising on other rocks only flow over limestone for a short distance and then disappear underground.

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  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.

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   When the water penetrates to the limestone base and meets non-porous rocks, it reemerges onto the surface as a spring or resurgence.

• 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 a uvula.

Some of them are a mile across, containing much clayey soil from the limestones, weathered after their subsidence.

• The Major Limestone Regions of the World. The most characteristic stretch of limestone occurs in northwest Yugoslavia. 

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

• Limestone vegetation in tropical regions, how- ever, is luxuriant because of the heavy rainfall all the year-round. 

• Settlements are 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 materials or quarried for the cement industry.

• The landforms of chalk are rather different from those of other limestones. 

• There is little or no surface drainage, and valleys which once contained rivers are now dry. 

• These are often called coombes. The chalk forms low rounded hills in southern and southeastern 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.

Features adorn the limestone CaFeatures of Limestone Caves:

• Stalactites


• Stalagmites


• Pillars

All of these features can be found adorning limestone caves. Stalactites hang from the ceiling of the cave, while stalagmites grow up from the floor. Pillars are formed when stalactites and stalagmites grow together over time. These features are created through the slow deposition of minerals in the cave environment.ves: Stalactites, Stalagmites, Pillars