How sinkholes form

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Posted: Thursday, November 14, 2013 12:07 pm | Updated: 9:05 pm, Tue Aug 12, 2014.

Sinkhole formation is again in the news.  Just to our north another large sinkhole has threatened a neighborhood and its residents forming suddenly and seemingly without warning.  How do these sinkholes form?

The geology of Florida is such that much of the state sits on a strata of limestone.  Through the limestone beneath the ground are a network of underground rivers and fresh water springs that make central Florida a wonderland for boaters, divers and fishermen.  The beauty of the natural springs is a must for every Floridian to see.

Yet the very nature of the geology of north central Florida causes the state to be susceptible to sinkhole formation.

Central Florida sinkhole

The key to sinkhole formation is the chemistry of limestone.  Limestone is a rock that is very easy to dissolve if it sits in water that is slightly acid.  The soil that we walk on sits over the limestone beneath. Rain water and  water from lakes and springs move through the soil and eventually downward into the limestone. On the journey downward the water may become acidified by the soil and carbon dioxide. As the water seeps into the cracks of the limestone it chemically reacts and dissolves the stone.  The cracks are then enlarged and let in more acid water and this dissolves more stone.  Eventually caverns in the rock form.

How sinkholes form (SWIFTMUD)

When the weight of the soil above becomes too great the cavern collapses and a sinkhole forms.

If you look at a map of sinkhole locations in Florida you will notice that most of the activity is well north of us.

Florida sinkhole locations

The reason for this is the difference in the geology of our soil.  There is a boundary between the soil and limestone that prevents the free percolation of water into the limestone in our area.  We also do not have the network of springs underground.  It is this difference in geology that makes sinkhole formation much more difficult on the Suncoast.

John Scalzi

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