how are sink holes created

Otjikoto Lake is a sinkhole lake, created by a collapsing karst cave near Tsumeb, Namibia. In June 1915 German troops dumped war materials in the lake Natural sinkholes occur when bedrock is dissolved by water, causing the ground above it to collapse. The bedrock typically consists of carbonate rock, such as limestone or dolomite. Rocks that readily dissolve in water are called karst. A sinkhole form when water falls onto an area composed of easily-dissolved rock and the water cannot drain out. A devastating sinkhole occurred in Florida on February 28, 2013, raising questions and concerns about this incredible phenomenon.