THE SCIENCE OF THE MISSOURI KARST
by RANDALL C. ORNDORFF
Geological science can benefit greatly from cave diving. Speleogenesis (the development of cave passages) is poorly understood since much cave development occurs below the water table in the saturated subsurface. Cave surveys, videography, and rock samples collected by cave divers gives scientists a better chance to understand how cave systems and large spring systems form.
The Ozarks of southeastern Missouri contains a world-class spring system with the highest concentration of large springs in the U.S. Protecting this natural resource is important for water quality, tourism in National and State parks, and an appreciation on how these large springs form.
Geologists from the U.S. Geological Survey are working with the Ozark Cave Diving Alliance (OCDA) to collect information from the springs to better understand the geologic controls on how Ozark caves form. The geologists had an idea on how the rock strata played a part in the formation of the cave, but they needed an accurate cave survey and rock samples from various areas to prove this idea. The great majority of the rock strata in this area are dolomite (a cousin of limestone) that dissolves to form the caves that dominate the region. Active solution of the rock occurs below the water table and when these caves intersect the surface, large springs form. However, there are a few beds of sandstone that are a part of the stratigraphic package. The idea is that ground water trapped beneath these sandstone horizons is under pressure and enhances the dissolution beneath the sandstone. Once the cave system gets large enough, it breaks through the sandstone and rapidly dissolves the dolomite above as the water works its way to the surface to form the spring.
Alley Spring, within the Ozark National Scenic Riverways (National Park Service), is an ideal place to test the idea. The OCDA found that the deepest part of the cave system, to date, is about 160 ft deep and levels out beneath a sandstone horizon. The cave survey verified depth and rock samples verified sandstone rock type. Information from the cave survey and the videography of Alley Spring show the cave system breaking through the sandstone bed in several areas. Future work by the OCDA in Alley Spring, and other Ozark spring systems, will help define the morphology of the cave system and help the scientists to understand Ozark springs and environmental affects on ground water.
Randall Orndorff, USGS