Karst landscapes are found throughout the world, varying from dotted hills to sinkholes, as can be found in portions of the central United States. The term “karst” is used to refer to a special type of landscape which results from the dissolution of the soluble rocks including but not limited to limestone and gypsum. The landscape is characterized by natural features such as caves and springs that provide water to more than 25% of the world’s population. The karst formation process is a geological process that takes many years, resulting in unique surface and subsurface formations, some of which form complex underground drainage systems and caves. Around 10% of the surface of the earth is taken up by karst landscape.
The process of karst formation is linked to what is called “carbon dioxide cascade.” The process takes place when the surface of bedrocks, especially around the cracks is broken down by the acidic water. Karst formation varies from region to region. As the rain passes through the atmosphere, carbon dioxide gets dissolved in the water. Once the rain droplets hit the surface, the water sips into the soil, dissolving more CO2 to form weak carbonic acid water. The infiltrated water erodes cracks and crevices in the rock. With the steady supply of carbonic acid water, carbonate bedrocks such as limestone and gypsum begin to dissolve. The openings on the bedrocks will become larger, with an underground drainage system beginning to develop, enabling large quantities of water to pass, and further increasing the rate of karst formation.
The process of karst formation may result in the formation of several large or small features both on the surface and beneath the ground. On the surface, small features such as runnels and limestone pavements can be formed in areas with a loose surface. Features such as sinkholes, vertical shafts, and disappearing streams are common on medium-sized surfaces. Some of the large-scale karst features include karst valleys and poljes. Complex underground drainage systems and large caverns and cave systems are formed beneath the surface. Another notable karst topography is the makatea surface which is common in the tropics, formed by erosion along the limestone shore.
Notable Karst Areas
Although karst features are spread across the world, especially in areas with soluble rock material, some features require an intense search to be noticed. Australia’s Nullarbor Plain is the largest limestone karst in the world. It occupies an area of approximately 77,000 square miles. Slovenia has some of the highest risk sinkholes in the world. Highland Rim in the western US is the second-highest risk of karst in the world. Mexico’s regions of Yucatan peninsula and Chiapas host some of the most important karst.
Karst Induced Environmental Problems
Shallow aquifers in karst areas are vulnerable to groundwater contamination, especially through agricultural activities and disposal of solid waste. Structures built within sinkhole plains are likely to experience flooding which may be aggravated by increasing rate of surface runoff or decreased storage due to the filling of the sinkhole. Sinkhole collapse may lead to a costly destruction of properties built on the surface. The collapse is often caused by a drop in the water table below the regolith-bedrock contact.