Limestone bedrock covered by clay soils may fail catastrophically and form a?

• A. Solution sinkhole
• B. Piping sinkhole
• C. Collapse sinkhole
• D. Cover-collapse sinkhole

Answer: (D)

Limestone is soluble, so karst landscapes develop underground voids as water dissolves the rock. When the surface is covered by clay soils, that cover can act like a rigid cap over a growing cavity. As the void enlarges, the supporting strength of the overlying clay and soil is lost. If the roof collapses, the entire cover drops suddenly, creating a catastrophic surface sinkhole. This is characteristic of a cover-collapse sinkhole: a rapid failure of the soil cover over a dissolved rock cavity.

The other types don’t fit this scenario as well. A solution sinkhole forms mainly from ongoing dissolution with surface subsidence that tends to be gradual rather than abrupt. A piping sinkhole involves vertical erosion of sediments by infiltrating water through pipes or tunnels, not the sudden collapse of a clay-covered roof over a void. A more general collapse sinkhole could describe the event, but the specific situation of a clay cover over dissolving limestone that fails violently points to cover-collapse as the correct description.