SEDIMENTARY ROCKS

Karst Topography

Karst Topography mainly related to geological work of ground water. The ground water does erosional work mainly by solution. The physical erosion is negligible as the groundwater moves very slowly through bedrocks. The erosive action of groundwater is most conspicuous in regions where easily soluble rocks especially limestone underlie the surface. The water charged with carbon dioxide dissolves limestone very easily. The common solution structures found in limestone are as follows.

Erosion features karst topography                                                                                                         

    • Sinkhole:-these are funnel shaped hollows of varying sizes which are made in the carbonate rocks by the solvent action of groundwater. A sinkhole may form when a cavern roof collapses or it may develop slowly as the material is dissolved and carried away in solution. In regions with many sinkholes streams are often absent as following a rainfall most of the runoff is funnel below the ground.
    • Caverns:- the tunnels underground chambers which are formed in limestone by the solution of rock by groundwater are called caverns. These stand without collapsing the roofs. Joints are the natural avenues through which groundwater moves. The dissolution of rock gradually enlarges the joints and produces a complex system of caverns. The caverns are believed to have formed at or just below the water table. The stream’s water may sometimes flow through these underground caverns.
    • Solution valleys:- solution valleys with continued solution of limestone the closely spaced sinks and solution basins are enlarged into a big valley called solution valley.
    • Karst topography:- the irregular terrain produced largely by the underground solution of limestone  is called  karst topography. The karst topography is characterized by numerous sinkholes, caverns and underground channels. This topography develops in humid climate.
    • Stylolites:-when groundwater percolates through bedding planes of limestone the more soluble parts are dissolved easily leaving the less soluble parts as ridges. In adjacent beds these ridges project into each other forming a zig zag lime along the junction of the bedding plane. Such a structure is called stylolite.

 

Depositional features of karst topography

  • Stalactite and stalagmite:-these features are found in caverns. As water drip from the roof of a cavern, evaporation leaves a small deposit of calcite behind. Gradually a cone shaped piller of calcium carbonate; hanging from the cavern roof develops. such a deposit is called stalactite. Similar deposits also grow from the floor of the caverns where water drop. Such piller like forms which grow upward from the cavern floor are called stalagmite. When a stalactite and a stalagmite meet a column or dripstone is formed.
Karst topography
Karst Topography
  • Geode:- sometime in the cavities of rocks the groundwater deposits crystals of quartz , calcite or other minerals. These deposits are called geode.
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