Figure 1: A huge sinkhole that destroyed
Figure 2: Another collapsing sinkhole that swallowed a building and a truck. Photo Courtesy of Geotimes.
Figure 3 : Arial photo of several sinkholes located
Figure 4: Process of developing a sinkhole. Diagram
Figure 6: The Wrath of the Sinkhole, destroying an
The Bright Side of Sinkholes:
Karst topography is a type of landscape where areas rich in carbonate rocks are sculpted by water (Tarbuck and Lutgens, 2002). Associated with karst topography is the development of sinkholes, which are depressions created by the removal of soluable rock by groundwater (Tarbuck and Lutgens, 2002). Since karst topography occupies approximately 10% of the Earth's surface, understanding the process and side-effects are important (GCRIO, 2002). Sinkholes can range from a meter to over 100 meters wide (Murck & Skinner, 1999). Areas that display karst topography and have potential for sinkholes development are portions of Kentucky, Tennessee, southern New Mexico, southern Indiana, central and northern Florida, and the Appalachian Mountain Great Valley Limestone Belt (Schmidt, 2001).
Conditions for Formations
Chemical weathering occurs with minerals that are of the
carbonate group, typically bedrock of limestone and dolostone. The reaction
that the water has on the rock will proceed to dissolve it (Murck &
Skinner, 1999). Less common, evaporite rocks are susceptible to the same
process, except at a much faster pace. For example, gypsum is 150-7,500
times more soluble than limestone (Martinez et al, 1998). So in these
areas the dissolution is very intense.
Since the bedrock in karst areas are typically limestone or dolostone, a reaction occurs with rainwater (which percolates down into the groundwater system). This reaction occurs because the water is mildly acidic (McKenzie et al, 2000). Carbonic acid, the most common acid in water, forms when water and carbon dioxide combine in the atmosphere (Carving Canada, 1995). Once the water reaches the bedrock, the chemical reaction begins. The acid then dissolves the carbonate minerals through this reaction:
CaCO3 + H2CO3
=> Ca+2 + 2HCO3 -1
(Formula from McKenzie et al, 2000)
Products of the Geologic Process
This process can take several years to develop a porous
medium that can transport groundwater (Carving Canada, 1995). Continuation
of this will then produce large cavities or caves. From these large voids
sinkholes are likely to form. Two different types of sinkholes develop
from this process, subsidence sinkholes and collapsing sinkholes.
Impact on Humans
The entire karst dissolving process can take several years to develop, however the actual release and formation of a collapsing sinkhole can happen in a matter of seconds. As seen in the figures, sinkholes can have damaging effects to large manmade objects. They are capable of destroying entire houses, swallowing portions of roads, or anything that sits above the unstable ceiling.
Carving Canada, 1995, [Online]: http://www.cancaver.ca/docs/karst.htm (2/5/02).
Hornsby, A.G., Sinkholes. [Online]: http://www.aterquality.ifas.ufl.edu/PRIMER/sinks.html (2/6/02).
Hubbard Jr., D.A., 1990, Sinkholes. [Online]: http://www.mme.state.va.us/Dmr/PUB/Brochures/sink.html (2/6/02).
Martinez, J.D., Johnson, K.S. and J.T. Neal, 1998, Sinkholes in Evaporite Rocks. American Scientist, v.86 Jan/Feb: p.38-51.
McKenzie G.D., Storm, R.N, and J.R. Wilson, 2000, Groundwater Processes, Resources, and Risks, Laboratory Manual in Physical Geology 5th ed., Upper Saddle River, New Jersey, Prentice-Hall, Inc.
Murck, B.W. and B.J. Skinner, 1999, Geology Today: Understanding Our Planet, New York, New York, John Wiley & Sons, Inc.
Schmidt, W., 2001, Sinkholes in Florida. Geotimes, v.46 May: p.18
Skinner, B.J. and Porter, S.C., 1992, The Dynamic Earth: An Introduction to Physical Geology 2nd ed., New York, New York, John Wiley & Sons, Inc.
Tarbuck, E.J. and F.K. Lutgens, 2002, Earth: An Introduction to Physical Geology 7th ed., Upper Saddle River, New Jersey, Prentice-Hall, Inc.
The U.S. Global Change Research Information Office, 2002, Karst Activity, [Online]: http://www.gcrio.org/geo/karst.html (2/6/2002).
White, W.B., Culver, D.C. and J.S. Herman,
1995, Karst Lands, American Scientist, v.83 Sept/Oct: p.450-9.
Author: Eric Scheumann
Creation/revision date: February 26, 2002
Copyright ©-2001 Earlham College. Revised 25 January 2002. Send corrections or comments to firstname.lastname@example.org