Indiana's Region of Karst Topography (GM-15)
Some rocks, limestone and dolomite in particular, are soluble in water. Weakly acidic rainwater seeping into joints and fractures of underlying carbonate rocks gradually enlarges them and eventually forms caves and other solution features. A region in southcentral Indiana is noted for these characteristic landforms, known as "karst" after a similar region in Yugoslavia.

Sinkholes are perhaps the most widespread karst feature. These funnel-shaped sinks may be broad, dish-shaped depressions of may have steep sides where surface materials have collapsed into underlying caverns. As many as 1,022 sinkholes were counted in 1 square mile in southern Indiana, each draining into a subterranean stream. Only a few of the largest streams can maintain their flow across the sinkhole plain and cave-riddled uplands. In the karst region, streams enter swallow-holes, leaving blind valleys and dry streambeds and emerging as springs miles away.

Solution-widened joints, usually filled with soil, are called "grikes" and can be seen in most road cuts and quarry walls. Upward projecting, usually very irregular surfaces of limestone in southern Indiana's karst area are called "lapies."

Our Hoosier State Beneath Us: Geomorphology