Tragedy struck a Florida home recently when the ground suddenly gave way to a sinkhole. In a matter of minutes, the sinkhole had swallowed up the home’s bedroom along with its occupant. The sink hole grew from 30 to 100 feet wide and is still in the process of settling. It's important to understand this phenomena isn't confined to Florida.
Why did this happen?
Sinkholes form in karst terrain, the name given to topography which occurs below the surface of the earth. A couple things are needed for this subterranean feature to develop: water-solubility of the bedrock and contact with ground water. The surface of the earth is comprised primarily of water. Of the land masses, approximately 10% is made up of limestone, 15% of the United States surface is limestone. Limestone or calcium carbonate (CaCO3), a sedimentary rock, is composed of calcium, carbon and oxygen. Groundwater is actually is a weak solution of carbonic acid, the result of water (H2O) and carbon dioxide (CO2) combining, and can easily dissolve limestone.
Karst terrain results as groundwater dissolves limestone. Invisible above ground, cavities even caves, are made over time. These, in and of themselves, don’t necessarily pose any risk. The tipping point, or more accurately, the caving in point is reached when the limestone has been dissolved to such a degree that the remaining ‘ceiling’ doesn’t have the structural integrity to continue to support everything above ground.
Sinkholes formed following a collapse in karst terrain is a ‘natural’ phenomena. Sinkholes also can be caused from man-made actions such as collapsing and/or compressing of buried, de-compostable material or after excavation work if the soil hasn’t been replaced and well-compacted.
How are sinkholes detected?
Most often sinkholes are detected as they’re discovered. Options to proactively discover potential sinkholes are limited, expensive and not conclusive. Knowing your local history and being aware of subtle settling signs offer the not much, but something to go on. Sinkhole.org lists signs to look for:
1. Cracks in interior joint areas, windows or doors
2. Cracks in exterior block or stucco
3. Windows or doors become harder to close properly
4. Depressions in your yard or the street or other yards nearby
5. Deep cracks and separation of paved concrete walks and drives
6. Circular patches of wilting plants
7. Sediment in your water
8. Neighbors have had or confirmed possible sinkhole activity
9. Observation of an actual cavity beginning to open
Visit their website for photographs accompanying each sign.
The University of Wisconsin’s Karst Topography provides a wealth of information. Note the distribution of karst topography in the United States. Though most states have some areas of karst terrain, this type of subterranean topography essentially includes entire state of Florida. All Floridians should be familiar with the signs of sinkholes to prevent or at least minimize the devastation of future sinkholes.