A depression or hole in the ground caused by some form of collapse of the surface layer is known as what?

A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are locally also known as vrtače and shakeholes, and to openings where surface water enters into underground passages known as ponor, swallow hole or swallet. A cenote is a type of sinkhole that exposes groundwater underneath. Sink and stream sink are more general terms for sites that drain surface water, possibly by infiltration into sediment or crumbled rock.

Classification:

1-Solution or dissolution sinkholes form where water dissolves limestone under a soil covering. Dissolution enlarges natural openings in the rock such as joints, fractures, and bedding planes. Soil settles down into the enlarged openings forming a small depression at the ground surface.

2-Cover-subsidence sinkholes form where voids in the underlying limestone allow more settling of the soil to create larger surface depressions.

3-Cover-collapse sinkholes or "dropouts" form where so much soil settles down into voids in the limestone that the ground surface collapses.

4-Pseudokarst sinkholes resemble karst sinkholes but are formed by processes other than the natural dissolution of rock.