How a Sinkhole Forms
| A sinkhole is a naturally occurring, usually cone- or bowl-shaped depression in the land surface formed as a result of the collapse of the soil cover into a crevice in the underlying bedrock, or the collapse of a cave roof and its overlying rock and soil cover into the cavity below. |
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Initially, a sinkhole forms as soil collapses into a crevice and is carried away through a conduit by water. |
Further collapse of the soil cover from below causes circular cracks to develop at the surface. |
Then the soil roof of the developing sinkhole falls into the hole to form a cylindrical cavity. |
Erosion by water flowing into this new drain hole smooths the hole's sharp edges to form the typical inverted cone- or bowl-shaped depression. |
Source: Illinois State Geological Service