Why Is Tampa a Sinkhole Vortex?

In a cave in the Tampa Bay area.  Photo by Grant Harley.
Caves, when they collapse, turn into sinkholes.

The tragic sinkhole death in the Tampa Bay area the other day is a stark reminder of the instability of the Florida landscape as a result of karst processes.  Karst is a term applied to landscapes that form in soluble terrain--usually with limestone or dolomite bedrock.

Limestone, with time, can dissolve in water to create small holes called vugs.  They can expand into caves and caverns that are interconnected.  The holes in the limestone in Florida are very interconnected and the bedrock is like Swiss cheese.  It is difficult to see the limestone in Florida because it is mostly covered by thick layers of sediment that were deposited during higher sea level stands in the past (one of the key pieces of evidence of past climate change).

The distribution of the holes in the bedrock vertically is highly dependent upon the location of groundwater and the proximity to the coastline.  However, the geographic distribution of the sinkholes is highly dependent upon how thick the sediment cover is above limestone.  South of Tampa and Orlando the cover over the limestone thickens.  Because of this, sinkholes in south Florida are relatively rare.  However, in an area extending from Tampa, Orlando, and Ocala, sinkholes are relatively common due to the thin cover of sediment on top of the bedrock.

Most of these sinkholes form naturally.  However, some can be induced by changing the subsurface hydraulic conditions by pumping water from the rock.  In addition, excess weight added to the surface can also induce them.

As I've mentioned in the past, hundreds of sinkholes form every year in Florida.  They cause tremendous property damage, but this recent death is the first known injury or death in some time.  If you are interested in sinkholes in the Tampa area, check out this article I wrote with Mario Parise and Dan Dye.