(World Geography) Karst Processes and Landforms - Characteristic, Erosional Features & Depositional Features


Concepts of Geography, Natural Resources


Limestone and chalk 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 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 than termed karst region.


Karst regions have a bleak landscape, occasionally broken by precipitous slopes. 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. 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.


Erosional Features

Limestones are well jointed and it is through there joints and cracks that rain-water 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, rectangular blocks are termed clints.


On the surface of the limestone are numerous swallow holes, which are small depression carved out by solution were rainwater sinks into the limestone at a point of weakness. They are also known as sink hole. Where a number of swallow holes coalesce a larger hollow is formed and is called a doline. Several doline may merge as a result of subsidence to form a larger depression called an uvala. Polje may be as large as a hundred square miles but there are partly due to faulting. Where subterranean streams descend through swallow holes to underground passages, the region may be honeycombed with caves and caverns. Vertical pipe like chasms that connect caves and swallow holes are ponores.

Depositional Features

Stalactites are slender growing pinnacles that hang from cave roofs. The water carries calcium in solution and when this lime-charged water evaporates, it leaves behind the solidified crystalline calcium carbonate. 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, fatter and more rounded. Over a long period, the stalactite hanging from the roof is eventually jointed to the stalagmite growing from the floor to form a pillar. All types of deposits in the caverns are collectively called speleothems.



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