Phosphate Mining Linked To Sinkholes
Sink Holes Defined
A Sinkhole is an area of ground that has no natural external surface drainage–when it rains, all of the water stays inside the sinkhole and typically drains into the sub-surface aquifers.
Sinkholes can vary from a few feet to hundreds of acres and from less than (1) foot to more than (100) feet deep. Some are shaped like shallow bowls or saucers whereas others have vertical walls; some hold water and form natural ponds or lakes.
Typically, sinkholes form so slowly that little change is noticeable, but they can form suddenly when a collapse occurs. Such a collapse can have a dramatic effect if it occurs in an urban setting.
Sinkhole formation data correlate directly to overburden removal practices from aquifer destruction and complete removal, such as practiced by the phosphate industry.
Southwest Florida Water Management believes…
When natural water drainage pattern is changed dramatically or when new water diversion systems are used, sinkholes may soon develop. Some sinkholes form when the land surface is changed as described above, such as when industrial phosphate run-off and materials settlement storage ponds are created.
The substantial weight of the new material can trigger an underground collapse of supporting material, thus causing a sinkhole.
The overburden sediments that cover buried cavities in the aquifer systems are delicately balanced by ground-water fluid pressure (surface materials back pressure). The water below ground is actually helping to keep the surface soil in place.
Ground-water pumping for phosphate mines is enormous based on a seemingly unending water supply, in the form of Florida’s aquifers. Draglines are used for moving millions of metric tons of surface materials known as Overburden. This results in a lowering of groundwater levels and underground structural failure.
Areas Prone to Collapse Sinkholes
Figure (2) below displays formations where underground cavities can form and catastrophic surface collapses will happen. These rock types are evaporites (salt, gypsum, and anhydrite) and carbonates (limestone and dolomite). Evaporite rocks underlie about 35 to 40 percent of the United States, though in many areas they are buried at great depths.
Map of the United States showing areas where rock that are prone to dissolution and sinkholes are prevalent. Central Florida is shown on the map to have karst rock along with gypsum very close to the surface. These rock types are prone to sinkhole formation. Historically, karst rock formations near the surface can be a deadly combination.