Cedar Sink

Cedar Sink is a vertical-walled large depression, or sinkhole, in the ground, that is located in Edmonson County, Kentucky and contained within and managed by Mammoth Cave National Park. The sinkhole measures 300 feet (91.4 m) from the top sandstone plateau to the bottom of the sink and was caused by collapse of the surface soil. The landscape is karst topography, which means the region is influenced by the dissolution of soluble rocks. Sinkholes, caves, and dolines typically characterize these underground drainage systems. Cedar Sink has a bottom area of about 7 acres (2.8 ha) and has more fertile soil compared to the ridgetops.

The rocks of Cedar Sink and the surrounding area are from the Mississippian (also known as Lower Carboniferous or Early Carboniferous) subperiod that occurred 358.9 to 323.2 million years ago.

The Big Clifty Sandstone caprock has been breached exposing the limestone Girkin Formation resulting in a relief between approximately 200 feet (61 m) below the main plateau surface. The bottom of the sink lies another 100 feet (30.5 m) below and exposes the top of the Ste. Genevieve Limestone.

The weakening of the ceiling from the breaching of the caprock and the formation of Smith, Cedar Spring, and Woolsey Valleys caused the ancestral master trunk to collapse. Continuous flow in the master drainage line further undermined the sink and triggered further collapse.

Collapse sinkholes, like Cedar Sink, form after an initial subsurface collapse occurs. This collapse commonly happens at the intersection of two passages underground where the roof span is the widest and therefore weakest. The process continues as the underground stream repeatedly undercuts the cave walls, inducing collapse of the weight-bearing cantilever beams resulting in a wider passage. Erosion continues and eventually the void reaches the surface.

Water in an ephemeral stream can be seen from the overlook and occasionally at six other places within this sink, based on the season and recent precipitation events.

...
Wikipedia