In regions where karst rocks are covered by another type of rock, sinks can form below the surface in the karst rocks. The evidence for this feature may be either a collapse or subsidence doline in the overlying impervious or insoluble bedrock. Subjacent collapse dolines form when a cave in an underlying karst rock collapses to produce a sink in the overlying bedrock. These dolines exhibit collapse features such as steep walls and an angular shape in plan. If no further collapse occurs, the walls of the doline can become smoother with weathering.
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