Water seeping through soil into bedrock dissolves
the rock along cracks and between layers (called bedding planes). As the cracks
get bigger, soil falls into them. Water flowing underground may also dissolve
and remove earth materials from below, so the land surface forms a bridge or
arch of soil over a hidden hold or cave.
The soil arch gets thinner and weaker as more
earth materials collapse into the buried hole or cave. The collapsing material
may fill up the hole and stop the erosion. But it it's removed from below by
flowing water the collapsing continues right up to land surface.
Circular cracks appear in the soil at the surface
just before a catastrophic collapse of the surface.
Water washing down the sides of the sinkhole
soon erodes the sharp edges into the smooth contours of the classic bowl-shaped
sinkhole.
