Sinkholes, also called sinks, develop slowly when the ground subsides a few inches a year or catastrophically when the surface drops tens of feet per second. A common instigator is groundwater that dissolves a sizable hole in an underground layer of halite (rock salt), gypsum, or other evaporite. If a void becomes so large that the evaporite layer can no long support overlying rocks and sediment, the ground sinks slowly or collapses quickly. Sinkholes also can be the result of underground mining, oil and gas operations, and other human activities.
A cavernous sinkhole that appeared suddenly in 2013 in a Wallace County pasture, for example, probably was caused by the natural dissolution of salt by groundwater. Conversely, a gaping hole that developed near Hutchinson in 1974 was related to decades of salt mining.
About a quarter of Kansas counties have sinkholes. Some occurred hundreds of thousands of years ago and others appeared virtually yesterday. They vary in size from smaller than a manhole to wider than a mile. Two older ones, Big Basin and its neighbor Little Basin in Clark County, likely have been fixtures in the state's landscape for a few thousand years.
KGS researchers use seismic reflection techniques to better understand the formation of sinkholes and identify sink-prone areas. Their past investigations have included a water-filled dip in Russell County that led to the demolition of an I-70 overpass and a catastrophic collapse in Pawnee County north of Macksville linked to a well used to dispose of saltwater brought to the surface when companies drill for oil.