What are common sinkhole signs to be aware of?

  • Cracks in the walls
  • Cracks around the door or window frames
  • Cracks in the floor or pavement
  • Cracks in and around the pool area
  • Cracks in the foundation or the structure separating from the foundation
  • Not being able to close doors and windows correctly
  • Pooling of water on the property
  • Slumping or slanting trees or sagging fencing
  • Wilting vegetation in small circular areas

But, what even causes them to begin with? Ruptured sewer lines contribute to some urban sinkholes, but generally they are naturally recurring phenomenon characterized by sudden settlement or collapse of land. Most of the time, they happen when underground water or seismic activity creates voids or chasms underneath the surface of the earth. When topsoil becomes heavy with rainwater, or is subject to some other stressor, or even simply from gradual groundwater erosion, the surface collapses into the void, and a sinkhole forms and swallows whatever was sitting on top of it.

Areas built on soft rock, such as limestone, and near underground aquifers are particularly susceptible to sinkholes. While they are found all over the world, the area’s most at risk in the United States are here in Florida along what many call Sinkhole Alley representing Hillsborough, Pinellas, Pasco, & Hernando Counties. 

Sinkhole Locations

Florida residents can look here to see where subsidence reports have been filed in their neighborhood. Click on the image to the right or the button below.

What Causes Sinkholes?

Water.

More specifically, sinkholes are the result of water collecting underground and lacking external drainage of some sort, according to the U.S. Geological Survey (USGS). As the water collects and circulates, it slowly erodes the bedrock and creates caverns and underground spaces.

Water can erode just about anything given enough time, but soluble minerals and rocks, like evaporaites (salt, gypsum) and carbonates (limestone, dolomite), are particularly vulnerable and can be worn away more easily than some other types of rocks and minerals.

Over time — often a very long time — these caverns grow and grow until the very top layer of the ground is no longer supported. Then the ground opens up and swallows anything sitting there, and you have a sinkhole.

Adding additional weight on the surface, be it buildings or just heavy rainfall, can break the top of such a cavity and create a sinkhole.