LIMESTONE (KARST) REGION
Meaning: Limestone or Karst region (Fig. 38.10) refers to a large stretch of land occupied by limestone which possesses a unique type of topography. Limestone is a sedimentary rock of organic materials made up of calcium carbonate.
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Characteristics of limestone region
- Solubility: Limestone is insoluble but is made soluble by the action of rain water which dissolves carbon dioxide to form a weak acid which in turn acts upon it (limestone) to make it soluble.
- Presence of depressions: Limestone region contains depression of varying sizes and depths.
- Absence of luxuriant vegetation cover in limestone region: There is a complete absence of thick vegetation cover in limestone region.
- Absence of surface drainage: Most surface water flows for a short distance and disappears underground due to easy permeability of the region.
- Presence of jointed and rugged topography: Limestone regions are well jointed, stony with a broken landscape.
- Presence of dry surface valleys: Due to easy penetration of water in limestone region, all the valleys are usually dry. Water, on the meeting hard rock underground may re-emerge below the limestone below the limestone as spring or
SURFACE FEATURES OF A KARST OR LIMESTONE REGIONS
- Grikes: Grike is a surface features in a limestone region. It is formed as a result progressive widening of cracks or joints by solution to form limestone pavement.
- Clint’s: Clint’s are surface features of isolated and rectangular blocks which exist between the joints or grikes.
- Shallow holes or sink holes: These are also surface features. They are small depression carved out by solution where rain water sinks into the limestone at a point of weakness.
- Dolina: This is formed when a number of several swallow holes join together to form large depression.
- Uvala: This result when several dolines join together to form a larger depression.
- Poljes: These are formed from larger depressions partly due to faulting.
UNDERGROUND LIMESTONE OR KARST FEATURES
- RESURGENCE OR SPRING: When water percolates the base of limestone, it re-emerges as resurgence. This is when the water reaches an impermeable surface before flowing horizontally. The stream in the landscape disappears through the swallow holes.
- CAVES OR CAVENS: These are underground features of karst regions. Some of these features may contain water or ponds. This feature is often linked by swallow holes and may contain stalagmites and stalactites. The caves are large underground spaces formed as a result of sinking and flowing of waters into the limestone through joints and bedding planes.
- STALACTITES: These are underground features of limestone region found in caves growing from up downwards and may join stalagmites to form pillars. Stalactites are sharp, slender and downward-growing pinnacles that hang from the roof of the caves formed when the water drips downwards.
- STALAGMITES: These features are also of underground limestone found in caves, growing from the grounds upwards and may stalactites to form pillars. These features are shorter, fatter and more rounded. They are formed when water drips down stalactite to the floor.
- LIMESTONE GORGES: These features are created when the vertical sides of an underground cave collapse or when a river cuts across and down into a limestone region.
- PILLAR: Natural pillar is formed by joining of the stalactite hanging from the roof to the stalagmite growing to roof 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.