Karst
Description
Karst is a distinctive topography that develops as a result of the dissolving action of water on soluble bedrock (usually limestone, dolomite, marble and, to a lesser extent, gypsum), which produces a landscape characterized by fluted and pitted rock surfaces, vertical shafts, sinkholes, sinking streams, springs, subsurface drainage systems, and caves. The unique features and three-dimensional nature of karst landscapes result from a complex interplay between geology, climate, topography, hydrology, and biological factors over long time scales.
How it is formed
The formation of karst in carbonate bedrock involves what is referred to as the carbon dioxide (CO2) cascade. As rain falls through the atmosphere, it picks up CO2, which dissolves in the droplets. Once the rain hits the ground, it percolates through the soil and picks up more CO2 to form a weak solution of carbonic acid.This mildly acidic water begins to dissolve the surface along fractures or bedding planes in the bedrock. Over time, these fractures enlarge as the bedrock continues to dissolve. Openings in the rock increase in size, and an underground drainage system begins to develop, allowing more water to pass through the area, and accelerating the formation of underground karst features.
Chemistry
Rain falling through the atmosphere picks up CO2, which dissolves into the droplets. The rain then percolates through the soil and picks up ore CO2, forming a weak solution of carbonic acid: H2O + CO2 = H2CO3 (the acid).
Hydrology
Water quality and quantity issues play an important role in karst terrain. The subsurface drainage networks associated with karst add a vertical underground dimension that can be difficult to define and understand. These underground hydrological systems can operate independently from the overlying surface drainage patterns, and sometimes cross topographic drainage divides. They are also capable of moving large quantities of water over great distances in relatively short periods of time.
The rapid transit times and limited natural cleansing and filtering mechanisms associated with subsurface stream systems can readily transport harmful materials, such as contaminants or sediments, from one area to another. These materials have the potential to seriously impact sensitive karst environments (e.g., surface and subsurface habitats, cave formations, and other secondary deposits), associated aquatic communities, and human water supplies. Variations in water quantity outside the range of natural conditions can alter both diffuse and discrete groundwater recharge rates to impact ongoing karst processes within the overall karst ecosystem.