11:32 am - Monday May 28, 2012

Sinkholes

A sinkhole, also known as a sink, shake hole, swallow hole, swallet, doline or cenote, is a natural depression or hole in the Earth’s surface caused by karst processes - the chemical dissolution of carbonate rocks or suffosion processes for example in sandstone. Sinkholes may vary in size from 1 to 600 meters (3.3 to 2,000 ft) both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may be formed gradually or suddenly, and are found worldwide. The different terms for sinkholes are often used interchangeably.

Types of Sinkholes

Since Florida is prone to sinkholes, it is a good place to use to discuss some different types of sinkholes and the geologic and hydrologic processes that form them. The processes of dissolution, where surface rock that are soluble to weak acids, are dissolved, and suffosion, where cavities form below the land surface, are responsible for virtually all sinkholes in Florida.

1. Dissolution Sinkholes
2. Cover-Subsidence Sinkholes
3. Cover-Collapse Sinkholes

Causes of Sinkholes

1. Water dissolved minerals in the rock, leaving residue and open spaces within the rock. (This is called “weathering”.)
2. Water washes away the soil and residue from the voids in the rock.
3. Lowering of groundwater levels can cause a loss of support for the soft material in the rock spaces that can lead to collapse.
4. Changing groundwater gradients (due to removing or introducing water to the system) can cause loose material to flush out quicker from the voids and the surface to collapse in response.
5. Any change to the hydrologic system (putting more water in or taking it out) causes the system to become at least temporarily unstable and can lead to sinkholes.
6. Sinkholes can result from seasonal changes in the groundwater table, freeze and thaw of the ground, and extremes in precipitation (drought vs heavy rain).

Impacts of Sinkholes

Sinkholes have very localized strusinkholesctural impacts, but they may have far reaching effects on ground water resources. Sinkholes can also impact surficial hydrologic systemslakes, streams, and wet lands by changing water chemistry and rates of recharge or run-off. Because the Earth’s surface is constantly changing, sinkholes and other subsidence features will continue to occur in response to both natural and human induced changes.

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