Sinkholes, like the one that killed a Florida man last week, and the one that appeared on a golf course in Illinois on March 8, are really just hidden holes in the ground.
Caverns are carved out by water in the ground, sometimes from heavy rains.
They are found throughout the world, but are more common in areas where the ground is made of soft rocks like limestone, gypsum or salt beds, called "Karst Terrain." The rain dissolves these rocks and creates giant caverns.
About 20 percent of the U.S. is underlain by this kind of ground, according to the USGS.
Usually sinkholes are slow forming and end up just making divots in the ground where the earth is being washed away under it. Like in this image:
Reuters
But some can be catastrophic, the top layer of the ground remaining intact while a huge cavern is carved out underneath, like the image below:
Reuters
When the cavern gets too big and the "crust" can't support itself anymore, it falls into the earth forming a sudden hole in the ground. These are the ones that make the news. Here are some areas where they are likely to happen.
Here's USGS geologist Randall Orndorff, explaining the science of sinkholes: