What are Sinkholes?

Sinkholes are a common feature of Florida's landscape, and being a resident of Florida myself, they are something I have become familiar with. 

Over the past month, they have become a major issue with many appearing in the corridor between Tampa and Orlando. In fact, they have had to close the Interstate #4 which connects Tampa and Orlando a number of times during the past three weeks due to sinkholes compromising the roadway and exits. So I thought it was a perfect time to take a minute and talk about what Sinkholes really are.

Sinkholes are only one of many kinds of karst landforms, which include caves, disappearing streams, springs, and underground drainage systems, all of which occur in Florida. Karst is a generic term which refers to the characteristic terrain produced by erosional processes associated with the chemical weathering and dissolution of limestone or dolomite, the two most common carbonate rocks in Florida. Dissolution of carbonate rocks begins when they are exposed to acidic water. Most rainwater is slightly acidic and usually becomes more acidic as it moves through decaying plant debris.

Limestone in Florida is porous, allowing the acidic water to percolate through their strata, dissolving some limestone and carrying it away in solution. Over eons of time, this persistent erosional process has created extensive underground voids and drainage systems in much of the carbonate rocks throughout the state. Collapse of overlying sediments into the underground cavities produces sinkholes.

When groundwater discharges from an underground drainage system, it is a spring, such as Wakulla Springs, Silver Springs, or Rainbow Springs. Sinkholes can occur in the beds of streams, sometimes taking all of the stream's flow, creating a disappearing stream. Dry caves are parts of karst drainage systems that are above the water table, such as Marianna Caverns.

And so, that's what a sink hole is--but let's hope we don't see too many more anytime soon! If you want to know more, I found a really great sinkhole Q&A sheet on the Florida Department of Environmental Protection Web site.