All Sinkholes Are Not Created Equal
By Reporting. Filed in Updates |Tags: florida insurance, sinkhole repair
Sinkholes are a commonly occurring geologic phenomenon just about everywhere. Florida is especially prone to sinkholes. Sinkholes are depressions or holes in the land surface. They can be shallow or deep, small or large. However in Florida, sinkholes are virtually all a result of the dissolving limestone.
There are several basic types of naturally-occurring sinkholes. They are:
Dissolution sinkholes form where sediment cover is either thin or absent above the carbonates, a condition that occurs along much of Florida’s Gulf Coast – from just north of Tampa Bay through the Big Bend area.
Dissolution of the limestone can be intensive where the water first contacts the rock surface. Aggressive dissolution can also occurs where water flow is focused in pre-existing openings in the rock, such as along joints, fractures, and bedding planes, and in the zone of water-table fluctuation where ground water is in contact with the atmosphere.
Cover-subsidence sinkholes tend to develop gradually where the covering sediments are permeable and contain sand. In areas where cover material is thicker or sediments contain more clay, cover-subsidence sinkholes are uncommon, are smaller, and may go undetected for long periods of time.
Cover-subsidence sinkholes develop slowly where the overlying soil and rock are thin. The water seeps through the overlying soil to the limestone beneath. The water moves slowly down through the limestone, dissolving the limestone as it moves further down, and taking with some dissolved carbonates and some of the overlying soils.
The result is typically a bowl-shaped sinkhole, often called a doline. Water often fills this type of sinkhole, creating ponds or lakes. In fact, most of Florida’s lakes are formed by this sinkhole activity.
Cover-collapse sinkholes can develop abruptly – over a period of hours – and cause catastrophic damage. Cover-collapse sinkholes occur where the covering sediments contain a significant amount of clay. Over time, the surface drainage, erosion, and deposition form the sinkhole into a shallower bowl-shaped depression.
