• Karst topography is formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum.
• It is characterized by underground drainage systems with sinkholes and caves.
• Karst is most strongly developed in dense carbonate rock, such as limestone, that is thinly bedded and highly fractured.
• Karst is not typically well developed in chalk because the flow of groundwater is not concentrated along fractures.
• Karst is most strongly developed where the water table is relatively low, such as in uplands with entrenched valleys, and where rainfall is moderate to heavy.
• Karsts are found in widely scattered sections of the world, including the Causses of France, the Kwangsi area of China, the Yucatán Peninsula, and regions in the United States.
• In India, karst topography is present in the Vindhya region, the Himalayas, Pachmarhi, Gupt Godavari Cave, the surrounding coast near Vishakhapatnam, and Bastar.
• Borra Caves, also called Borra Guhalu, are located on the East Coast of India, in the Ananthagiri hills of the Araku Valley.

Limestone & chalk

• Limestone and chalk are sedimentary rocks of organic origin.
• They are formed from the accumulation of corals and shells in the sea.
• Limestone is made up of calcite or calcium carbonate, along with magnesium in the form of dolomite.
• Chalk is the pure form of limestone and is white and 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 possesses a distinct type of topography termed as Karst region.

Characteristics of Karst Landforms

• Karst regions have a bleak landscape, occasionally broken by precipitous slopes.
• Most of the surface water percolates underground, hence surface valleys are generally dry.
• Streams generally cut their way along the joints and fissures of the rock, wearing out a system of underground channels.
• Water reemerges onto the surfaces as a spring or resurgence when it penetrates to the base of the limestone and meets the non-porous rocks.
• Rainwater finds its way into the underlying rock through joints and cracks in the well-jointed limestone.
• Enlarged cracks are called Grikes and isolated, rectangular blocks are termed as clints.
• Swallow holes are small depressions carved out by solution on the surface of limestone, where rainwater sinks into limestone at the point of weakness, also known as sinkholes.
• A larger hollow is formed when a number of swallow holes coalesce, which is called a Doline.
• Several dolines may merge as a result of subsidence (gradual caving) to form an even larger depression called an Uvala.
• Some very large depressions called Polje may be as large as 100 square miles, produced partly due to faulting.
• Subterranean streams which descent through swallow holes to the underground passes lead to the formation of caves and caverns which may contain ponds or lakes.
• The most spectacular underground features that adorn the limestone caves are stalactites, stalagmites, and calcite pillars.
• Water carries calcium in solution, and when this lime-charged water evaporates, it leaves behind solidified crystalline calcium carbonate.
• Stalactites are sharp, slender, downward-growing pinnacles that hang from the cave roofs.
• When moisture drips from the roof, it trickles down the stalactites and drops to the floor, where calcium is deposited to form Stalagmites, which are shorter, fatter, and more round.
• Over a longer period, the stalactite hanging from the roof is eventually joined to the stalagmite growing from the floor to form a pillar.

Erosional landforms of Karst topography

• Blind Valley:
  • A steephead valley or blind valley is a type of valley with a flat bottom and a steeply rising head.
  • It has an abrupt ending and does not continue further.
  • It is formed by the underground passage of a watercourse that was previously on the surface.
  • The watercourse resists the karst processes that shape the surrounding landscape and remains on the surface until it meets a non-porous layer.
  • At this point, the watercourse sinks underground, leaving behind a steephead valley.
• Swallow Hole/Sinkholes/Doline:
  • A sinkhole is a depression or hole in the ground caused by surface layer collapse.
  • Sinkholes are often caused by karst processes, such as chemical dissolution of carbonate rocks or suffosion processes.
  • Surface streams disappear underground through swallow holes.
  • Sinkholes have different local names such as Black hole for sea water, Blue hole for deep under water, Cenotes in Belize, Sotanos in Mexico, and Tomo in New Zealand.
• Clift:
  • a dipped part of a solution hole over time.
• Pinnacles:
  • vertical rock blades sharpened by dissolution.
• Lapies/Karren:
  • ridge-like features formed by differential solution activity along parallel to sub-parallel joints.
• Limestone Pavements:
  • a smoother form of lapies.
• Sinking Creeks/Bogas:
  • water lost through cracks and fissures in the bed, and if their tops are open, they are called bogas.
• Karst Window/Fenster:
  • a geomorphic feature formed from the dissolution of carbonate bedrock. It is caused by a caving in of portions of the roof of a subterranean stream, thus making some of the underground stream visible from the surface. 
  • When a number of adjoining sinkholes collapse, they form an open, broad area called a karst window.
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• Uvalas:
  • large karst depressions with gentle slopes and complex three-dimensional shapes that result from the coalescence of multiple smaller sinkholes.
• Polje:
  • a large flat plain found in karstic regions, usually 5 to 400 km² in size.
• Pools:
  • an opening at the top with water collected in the void of the surface with varying depth.
• Caves/Caverns:
  •  underground caves formed by water action in a limestone or chalk area; formation is prominent in areas with alternating beds of rocks or in areas with dense, massive limestone beds.
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• Karst Lake:
  • formed as a result of a collapse of subterranean caves, especially in water soluble rocks like limestone, gypsum, and dolomite; shallow lakebed is usually an insoluble layer of sediment so that water is impounded, leading to the formation of lakes.
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Depositional landforms of Karst topography

• Speleothems:
  • Deposits in caverns are called “speleothems”.
  • Calcite is the common constituent of speleothems.
  • Speleothems form due to carbonate dissolution reactions in calcareous caves.
  • They can take different forms depending on their depositional history and environment.
• Stalactites & Helictite:
  • Stalactites form when water containing limestone in solution seeps through the roof of the cave in the form of drops.
  • A small deposit of limestone is left behind on the roof, contributing to the formation of a stalactite that grows downwards.
  • Stalactites have a broader base than their free end.
  • Helictites are stalactites that extend horizontally or diagonally.
  • 
• Stalagmites & Halagmite:
  • A stalagmite is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from the ceiling drippings.
  •  It is an upward-growing mound of mineral deposits that have precipitated from water dripping onto the floor of a cave.
  • Ones that extend horizontally or diagonally from stalagmites are known as Halagmite.
  • 
• Cave Pillars:
  • Pillars in caves are formed by the fusion of stalactites and stalagmites.
• Drapes/Curtain:
  • needle-shaped dripstones hanging from the cave ceiling.
• Tufa:
  • a variety of limestone formed from precipitation of carbonate minerals from ambient temperature water
• Travertine:
  • a sedimentary rock formed from calcium carbonate minerals precipitated from freshwater, often in springs, rivers, and lakes
• Drip Stone:
  • calcium carbonate rock deposited in caves by the precipitation of calcite from water as excess dissolved carbon dioxide diffuses into the atmosphere
• Terra Rossa:
  • a reddish, clayey to silty clayey soil with neutral pH conditions

Human activities of Karst region

• Karst regions have little soil and vegetation due to the porosity of the rocks and lack of surface drainage.
• Limestone typically only supports poor grass due to these factors.
• Vegetation in tropical regions with heavy rainfall can be more abundant in limestone areas.
• The only mineral commonly found in association with limestone is lead.
• Good quality limestone is used for building materials and is quarried for the cement industry.