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Karst Topography

Karst Topography: requirements for karst cycle, role of limestone and dolomite, surface and subsurface landforms, climatic conditions and resurgence

Introduction

Originally limestone was found in the sedimentary rocks. The composition of the limestone in its pure state is calcite or calcium carbonate. Magnesium is also present in the limestone, and it is termed dolomite. It is soluble in rain. The conditions involved in the formation of karst topography are

  • Karst topography takes place in the region with a large stretch of water-soluble rocks
  • Limestone should be present at the surface level and also at the subsurface level
  • There should be no porous limestone in that particular area
  • The rock layer should be dense with no gaps in joints
  • The perennial source and low water table are some of the salient features of Karst topography
  • The area should have low rainfall
  • Heavy rainfall leads to the desolvation of rock

Features of Karst Topography

  • Swallow Hole in Section
  • Cave in Section
  • Sinkholes
  • Valley Sinks or Uvalas

(i) Swallow Hole in Section: Surface water and groundwater will vanish in the hole. The other name of Swallow holes in the section are Ponor and Serbo-coat

(ii) Cave in section: Due to the heavy running of surface water, cavities are formed in the rock. The formation of the cavity is due to erosion.

(iii) Sinkholes: Sinkholes are considered as the depression on limestone. Transformation of shallow saucer shapes to the funnel-shaped or cylindrical pipe. It is one of the usual features in the karst topography. The average depth of the sinkhole should be around 3 to 9 meters.

(iv) Valley sink or Uvalas: In the case of valley sink, depression becomes very wide.

Karst Landforms

Karst Landforms are made up of limestone. It is found in the Karst regions in the Balkans adjacent to the Adriatic sea. Karst landforms include:

  • It is one of the most major conditions present in limestone or dolomite regions
  • Produced by the action of groundwater
  • Through the process of solution and deposition

Mechanism of erosion in Karst region

  • Rocks should be permeable
  • The arrangement should be well structured and should be well joined
  • The surface should be absent from drainage facilities so that the water can be drained by the underground drainage
  • After some depth, horizontal movements of water follow the vertical movements
  • This horizontal movement allows the water to flow through the bed planes
  • The water also flows through joints and all the materials by themselves
  • The erosion of rock takes place by the downward and horizontal motion of the water
  • Erosion takes place by the chemical process of solution and precipitation, deposition by surface water and groundwater
  • Landforms developed in the dolomites region are rich in calcium carbonate

Karst Erosional landforms

Sinkhole

  • It happens when the rainfall hits the limestone at the point of weakness
  • Sinkholes are considered to be the depression of limestone
  • Transformation of shallow saucer shapes to the funnel-shaped or cylindrical pipe
  • It is one of the usual features in the karst topography
  • Size varies from square meter to hectare
  • The average depth of the sinkhole should be around 3 to 9 meters
  • The hole size will gradually increase due to continuous solvent action
  • The sinkhole is also referred to as a solution sink

Doline

  • It is also called a Collapse sink
  • It is less common in Karst topography

Uvalas

  • The depression is long, narrow to wide trenches
  • It is also called Valley sinks
  • The Uvala is the result of the merging of the Solution sink and Collapse sink
  • It may lead to a larger depression

Lapies or Karren

  • It occurs due to different solution cations at the parallel and sub-parallel joints
  • The Lapies may pave the way for the transformation of smooth limestone pavements
  • Lapies are grooved, flute, and ridge-like structures

Limestone Topography

Limestone Topography pavements

  • It is one of the natural karst landforms
  • It resembles artificial platforms
  • The pavements are flat surfaces decorated with limestone
  • Due to solvent action, progressive enlargement and widening of limestone take place
  • It also leads to the formation of cracks in trenches
  • The term “grikes” refer to the enlargement of joints
  • The term “clints” represents isolated and rectangular blocks

Caves

  • It is more common in areas where limestone is present between the rocks or in areas where limestone is very massive and dense
  • The percolation of water through the horizontal movement through cracks or joints forms caves
  • The filter of water along the bedding planes aids in the widening of the caves
  • The limestone gets dissolved between the planes
  • It results in the formation of gaps
  • This gap is termed caves

Polije

  • It is a huge flat-floored depression in the karst topography
  • It happens due to the merging of Valley sinks or By faulting
  • Found in tropic and subtropic latitudes
  • Sometimes it may also be seen in temperate regions and also in boreal regions
  • Dry areas are covered by thick segments and are rich in fertility
  • It can be used for agricultural purposes

Ponor

  • Natural opening surface
  • Located underneath the sinkhole
  • It is considered as a portal where the lake and surface water flows into the karst groundwater system

Landforms Due to Depositions

The deposition in Karst topography is mainly due to calcium carbonate. It gets dissolved and starts to precipitate when the solution is supersaturated and evaporation is more.

The spectacular features of landforms are

  1. Stalagmites
  2. Stalactites
  3. Pillars

Stalactites

  • These structures hang from the rooftops of caves and are of different shapes such as sharp, slender with varying diameters
  • It is broad at base and point at free ends
  • When water and lime meet, evaporation takes place, and crystalline calcium carbonate is left behind

Stalagmites

  • This type of formation is due to the dripping of water from a thin pipe
  • Dripping water from the roof forms Stalactite, and when it is from the surface, it forms Stalagmites
  • The shape of Stalagmites may be a column or a disc
  • Sometimes, it is either a smooth, rounded, bulging end or a miniature crater-like depression

Pillars

  • It happens when stalactite and stalagmite merge
  • The shape of the Pillar is a column and appears in a different size

Conclusion

In Karst topography we have covered all features of karst topography, erosional landforms such as pools, sinkholes, Lapies, limestone pavements, caves, collapse sinks etc. We also saw the depositional landforms of karst topography such as stalactites, stalagmites and pillars.