How are Sinkholes Formed?

Sinkholes can be developed in a short amount of time due to the highly soluble material and can be either natural or due to human intervention. Sinkholes can be developed naturally in carbonate rock such as limestone, they can also be formed in highly soluble evaporite rocks such as gypsum and salt (Martinez, Johnson, Neal, 1998, p. 38).

Out of the common rocks, evaporite rocks have the highest solubility, about 150 to 7,500 times more than limestone. When this rock comes into contact with unsaturated water they dissolve quickly. The fast dissolvent of rocks allows the creations of channels. Soon after, orifices and channels are augmented, allowing a greater amount of water through. As water flows down through the augmented cavities, it brings downs the surface material.Eventually the surface above collapses into the cavities (Martinez, et al., 1998, p. 38). 

Martinez, Johnson, Neal, 1998.

Evaporite rocks lie beneath 32 states of the continental United States. Evaporite rocks Underlie 35 to 40 percent of the 48 contiguous states.

Human Made Sinkholes

Sinkholes can also be the result of human intervention, usually they are caused by over-extracting of water, minerals, oil, etc. The mere extraction is not the direct cause of the ground collapsing, it is the events that take place after a work-site is abandoned and not refilled.

The mining of salt is one example of how human intervention created sinkholes. The drilling through or into rock salt has created many man-made sinkholes. Texas, Kansas, Louisiana and New York are among the states most affected by man-made sinkholes due to such drilling ((Martinez, et al., 1998, p. 38-39).

This is how an oil well can contribute to the formation of sinkholes.

United States Geological Survey.

Fresh water from the surface or aquifers -underground water supplies- flows down the oil well and it dissolves the salt in an underlying formation. The result is a brine -water saturated or strongly impregnated with salt- and a cavity. Eventually, the roof of such cavity collapses and creates a sinkhole.

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Works Cited