Approximately 20% of the U.S. lies in “karst terrain” -- areas where rocks below the surface can be dissolved naturally by water, making the ground more vulnerable to sinkholes.
According the USGS, a sinkhole is an area that has no natural external surface drainage. When it rains, water is trapped inside and it drains onto the subsurface.
It isn't exclusively a natural phenomenon. Human activity can also cause sinkholes, which can form over mines, washed-out sewers, and ground construction sites.
They can be hard to predict, and a reliable testing method has yet to be developed.
But the USGS is hoping to change that by developing geological maps that identify karst regions.
"Starting with science is important to understanding where sinkholes are likely to occur and making the best decisions to protect life and property," the agency explains in a blog post.
"Scientists at the U.S. Geological Survey ... play a key role by developing geologic maps of the nation."
People living in high-risk areas should survey their land for small holes or cracks in their home's foundation. Homeowners can also check with local surveys to see if their area is underlain with soluble rock.