In time, the vadose waters seeping down through bedrock fissures reach an
area where all these cracks and pores are already filled -- the phreatic
zone or water table. Here, the water moves laterally along bedding
planes, slowly dissolving still more of the bedrock, and joining other
waters until they eventually emerge in the form of a spring.
This particularly well- developed spring is the Orangeville Rise. This National Natural Landmark is also part of the Lost River system. Drainage from more than 40 square miles of property to the north and northeast finds its way through underground channels to resurface here, forming a "new" headwaters for Lost River. The Lost River itself sinks over 7 miles east of this location, and eventually joins these waters at a similar rise pool about a mile downstream from Orangeville.
As surface streams deepen their valleys, the water table lowers and these phreatic passages drain, allowing air to enter. Thus, most solution caves are drained spring- water conduits. From this point, the primary mechanism for enlarging the passage is erosion, although some dissolution still takes place. The hardness of the rock, orientation of the original fissures, prevalence of vadose versus phreatic dissolution, and amount of subsequent erosion all determine the final structure of the resulting cave passages.
Photo courtesy J Adams / Indiana Cave Survey