Karst region refers to large stretch of land occupied by limestone which possesses a unique type of topography. Limestone is a sedimentary rock of organic materials made of calcium carbonate. Karst landscapes develop where the bedrock is comprised of an extremely soluble calcium carbonate rock, for example: limestone, gypsum, or dolomite. Limestone is the most soluble calcium carbonate rock. Consequently, most karst regions develop in areas where the bedrock is limestone. Karst regions occur mainly in the great sedimentary basins. The United States contains the most extensive karst region of the world. The Mammoth cave system is located in this area. Other extensive karst regions can be found in southern France, southern China, Central America, Turkey, Ireland, and England.
Karst regions are formed when there is a chemical reaction between the groundwater and the bedrock. As rain, streams, and rivers flow over the earth’s surface, the water mixes with the carbon dioxide that naturally exists in air, and the soil becomes acidic and corrodes the calcium carbonate rock. The carbonate solution seeps into fissures, fractures, crevices, and other depressions in the rock.
Limestone region has no surface water, since the sudden disappearance of springs underground to form subterranean streams.
Famous Karst Locations
- The region of the Ozark Plateau in the Ozark Mountains of Missouri and Arkansas has many karst areas of limestone cliffs and other rock formations. The Arbuckle Mountains of Oklahoma contain much uplifting of limestone layers. Streams and waterfalls dissolve and carry the limestone downstream, coating some areas under and near the waterline with limestone deposits.
- The area of Turner Falls has the most of these. The world’s largest single formation of limestone exposed at the surface, and perhaps the world’s largest karst formation, is the Nullarbor Plain of Australia covering approximately 77,000 square miles.
- Many caves, blowholes and sinkholes can be found along the coast line and up to several hundred yards inland. Limestone cliffs overlook the southern Australian coast from the karst plain. Further inland there are potholes in the limestone and other less prominent features.
- The Chocolate Hllls are peculiar smooth conical-shaped karst formations on the Island of Bohol in the Philippines. They are a form of limestone with grass growing on their surface. When the grass turns brown in the dry season, their appearance is like bonbons or chocolate kisses. How they were formed is a mystery that is difficult to explain. Heavy rainfall may have helped to erode their surface during formation.
CHARACTERISTICS OF LIMESTONE REGION
- Owing to easy penetration of water in limestone region, all the valleys are usually dry. Water, on meeting hard rocks underground may re-emerge below the limestone as spring or resurgence.
- Limestone region contains depressions of varying sizes and depths.
- Limestone is insoluble but is made soluble by the action of rainwater which dissolves carbon dioxide to form a weak acid which in turn acts upon it (limestone) to make it soluble.
- There is complete absence of thick vegetation cover in limestone region.
- Limestone regions are well jointed, stony with broken landscape.
- Most surface water flows for short distance and disappears underground due to easy permeability of the region.
THE FEATURES OF SURFACE KARST OR LIMESTONE REGION
- Grikes: Grike is a surface feature in a limestone region. It is formed as a result of progressive widening of cracks or joints by solution to form limestone pavement. Such enlarged pavements or joints are called grikes.
- Clints: Clints are surface features of isolated and rectangular blocks which exist between the joints or grikes.
- Sink holes: These features are the results of small depression shaped by solution where rainwater sinks into limestone at the various points of weakness.
- Doline: This is formed when a number of several sink holes join together to form a large depression.
- Uvala: This results when several dolines join together to form a larger depression.
- Poljes: These features are large depressions created by faulting in limestone regions of the world.
UDERGROUND FEATURES OF A KARST OR LIMESTONE REGION.
- Caves or Caverns: These are underground features of limestone region. It is linked to the surface by swallow holes and may contain stalagmites and stalactites. They are large underground spaces formed as a result of the sinking and flowing of water into the limestone through joints and bedding planes. The large space created may contain ponds or lakes at the bottom.
- Limestone gorge: This has vertical sides formed when the roof of an underground cave collapses or when a river cuts across and runs down into a limestone region.
- Resurgence or springs: These result from water sinking into the underground. When the water meets hard rocks underground, it re-emerges below the limestone to form springs or resurgence.
- Stalactites: These are underground features of limestone region found in caves and they grow from up, downwards and may join stalagmite to form pillars. They are sharp, slender and downward growing pinnacles that hang from the roofs of the caves. Stalactites are formed when water dripping down into the cave carves out sharp and slender pinnacles. They are precipitates of calcium carbonate in solution of the underground water.
- Stalagmites: These are also underground features of limestone region. They are found in caves and they grow from ground upwards and may join stalactite to form pillars. They are shorter, fatter and more rounded. Stalagmites are formed when water drips down stalactite to the floor; evaporation then occurs while calcium is deposited leading to the formation of stalagmite.
- Pillar: Natural pillar is formed by the joining of the stalactite hanging from the roof to the stalagmite growing from the floor of the cave.
IMPORTANCE OF LIMESTONE REGION TO MAN
- Limestone region provides limestone which is an essential raw material for cement making.
- Limestone is also used in smelting of tin and iron.
- The limestone region is also a beautiful area of tourism.
- It is also a source of underground water.
- It also ensures or provides grazing land for animals.