A sinkhole is a depression or cavity in the ground which is caused by water erosion. Water erosion is a naturally occurring process in which water wears off soil and rocks.
The upper layers of the soil comprise of sand, clay, etc. While the bottom most layer called bedrock has rocks. Generally, sinkholes form in places where the bedrock layer has rocks made up of limestone or dolomite.
When rain falls, it seeps into the soil reaching the bedrock. Over time, the water dissolves these rocks and thus, erodes them forming hollow cavities. As these cavities get bigger, the ceiling of the cavity, that is, the upper layers of soil cannot hold the weight, hence they collapse forming sinkholes.
