It's like a think that's in the ground and it usually on the roads or in a field but they just callaps in and then you fall in it if you were on top of it or whatever was on top of it .. It's really scary I saw that in the news . :(
Sinkholes are depressions that occur when soil or bedrock has been removed and only air remains -commonly when the rock below the land surface is limestone carbonate rock or salt.Beds that have been naturally dissolved by ground water circulating through them and then the water dries up.
Before the sink hole forms, the surface will look fine. But it could be egg-shell thin since nature has been hard at work using water to move the solid material to someplace else.
Some of the news articles & photographs on the web involve bizarre cases of sinkholes swallowing a city block, a huge chunk of forest, or an SUV that seems to have fallen a full story into the hole that was a city street a second ago. Lots of weird sink hole pictures on the internet. Truly, truly bizarre effect of erosion at work.
I guess it's technically erosion underneath the ground that we don't notice until the hole finishes "digging up" or something heavy or forceful finishes the job in one fell swoop. I can think of a few ways things can erode above ground, but I can only think of water eroding things beneath ground, there may be more though.