Hydrology of Sinkholes
 Florida is dominated by the sedimentary rock known as limestone, a rock made of the mineral calcite (calcium carbonate).  The mineral calcite is very susceptible to weak acids, it dissolves quite readily; statues, buildings and headstones made of limestone or marble (a cooked version of limestone) are often pitted and corroded from acid rainfall.  Acid rainfall (either naturally acid or artificially acidic) falls on the Florida limestone, and combined with soil acids, produces a powerful dissolving agent that eats away at the limestone bedrock.  The acid waters percolate and infiltrate into cracks in the limestone, penetrating far underground.  Acid groundwater moves slowly through the limestone, dissolving the calcite and carrying it away as groundwater flows from high spots to low spots.

 The result (over many years) is a system of underground caves and caverns, partially or completely filled with groundwater.  The roofs of these caverns can collapse, producing sinkholes.  Withdrawal of groundwater and lowering of the water table (the top of the water saturated ground) is one of the main causes of collapse of cave roofs, because the groundwater filling the cave partially supports the cave roof.  The water table can be lowered naturally during drought, and lowered artificially by excess groundwater withdrawal from wells (especially agricultural or industrial wells) or by draining wetlands.  The sinkholes can be dry but are usually partly filled with water, forming lakes.  On the Lake Wales map, sinkholes are shown by closed contours with tick marks (hachures) on the contour lines, indicating a depression or basin; the sinkholes look like bomb craters.  Note that the topography of southern Florida is not quite as dramatic as the contour lines might suggest; the contour interval is only 5 feet on the Lake Wales map.

 Sinkholes are a hazard throughout Florida and other parts of the southeastern United States.  Sinkholes can form without warning, swallowing houses and other buildings.  Sinkhole hazards are found at:   http://web.ngdc.noaa.gov/seg/hazard/resource/geohaz/sinkrsch.html
 

Aerial photo of sinkhole at Winterpark, near                 Ground level view of sinkhole at Winterpark.  Water table not visible.
Orlando, Florida.  roads for scale

    Information on Lake Annie sinkhole and the Lake Wales region can be found at:  http://www.archbold-station.org/abs/regionalecol/lkannie.htm

Information on Florida sinkholes in general can be found at http://www.dep.state.fl.us/geology/geologictopics/sinkhole.htm

 The size of sinkhole lakes in Florida is probably related to the size of the original cavern or cave.  As can be seen on the map, there are many small sinkholes and a few larger ones.  Some of the larger lakes do not have the characteristic "bomb crater" shape, and may not be water-filled sinkholes.

 The lakes in Florida represent places where the groundwater is at the surface; Florida lakes are not "bowls of water" sitting on dry ground, but instead are expressions of the water table intersecting the topography.  The elevation of a lake is the elevation of the water table at that locality.  With the large number of lakes in the quadrangle, you can easily map out the water table; the water table is highest in the western part of the map, and lowest in the east, indicating that groundwater is flowing underground from west to east.

 Human activities in Florida are both creating and destroying lakes and wetlands.  Lakes are decreased in size or completely destroyed by lowering the water table through artificial drainage and groundwater withdrawal, and by infilling lakes.  Paradoxically, lakes are also created when groundwater levels are artificially lowered, forming sinkholes.
 
 
 

go to top of page