Florida Geography – What makes our area unique!
I hosted an educational program on springs, sinkholes, and karst topography earlier this week. Participants seemed to really perk up when I explained why springs and sinkholes are not evenly distributed throughout the state of Florida. Seeing as how this information seemed to be a hit, I thought I would pass this information along.
To start off, we’ll have to go way back in time…somewhere around 25 million years ago to be exact. At this time, the first of two episodes (think moving tectonic plates) occurred that created the Ocala Uplift. The term “uplift” is used instead of “mountain” because it’s less than 100 ft. above sea level.
Over the last several millions years, much of the sand and clay that covered the Ocala Uplift has been removed by wind and rain. Therefore, the limestone is very close to the surface, somewhere between 0 and 50 feet. This creates an environment perfect for springs and sinkholes. First, it exposes the limestone to weathering and dissolution by slightly acidic rainfall. As the limestone dissolves, it creates cracks, crevices, and sinkholes close to the surface of the land that are readily visible. Secondly, since much of the overlying clay and sand has been removed, groundwater is able to move freely up and down in the limestone in what is called an unconfined aquifer. When the groundwater table is high enough, sinkholes fill up with water forming ponds and lakes and sometimes springs.
Western Marion County is also good horse county. This is primarily because the limestone close to the surface provides good drainage and is, therefore, good for growing grass.
Ocala Uplift – This map shows the extent of the Ocala Uplift in Florida.
Springs of Florida Map_11X17, REported Sinkholes in Florida – The maps show the location of springs and sinkholes in Florida. Notice how the locations line up closely with the location of the Ocala Uplift.
Confined & Unconfined Aquifer – This maps shows the location of confined and unconfined aquifers in Florida. Notice again how the location of springs and sinkholes overlays areas where the aquifer is unconfined. The areas in blue are where limestone can be found very close to the surface of the land.