In 2013, a Wallace County sinkhole in far western Kansas appeared without warning and then grew to more than 200 feet across and 90 feet deep. The KGS determined that natural dissolution of underground halite (rock salt) likely caused the catastrophic collapse. During the dissolution process, groundwater seeped through fractures in layers of Cretaceous chalk and slowly dissolved a substantial hole in the 2,000-foot-deep and 200-foot-thick bed of halite. When the salt bed could no longer sustain the weight of higher rock layers, everything from the surface on down collapsed into the void.
Much of what is known about the state's subsurface geology has been learned through data collected during oil and gas and mining activities. Because northeastern Wallace County is short on oil and gas and its salt is too deep to mine economically, data about the subsurface geology there is limited. However, by extrapolating data collected from wells in other parts of Wallace County and western Kansas, KGS scientists determined that the Permian-age salt bed probably extends beneath the site of the collapse, making dissolution of the salt by groundwater the apparent culprit.
Although the 2013 sinkhole is unusual, it is not unique. Several historical collapses have been documented in Wallace County alone, including the circular Old Maid Pool about six miles northwest of Sharon Springs. Although the age of the Old Maid Pool is unknown, R. C. Moore, director of what was then known as the State Geological Survey of Kansas (now the KGS), estimated it was decades, if not hundreds of years, old when he first saw it in 1926. Moore had made the trip to Wallace County to investigate a newly collapsed sinkhole discovered by a rancher investigating a suspicious cloud of dust.