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Karst Country


Sat, Jan 13th, 2001
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A landscape that needs special careBy Nancy OvercottMonday, January 15, 2001

We live in a beautiful part of the world, but under our feet is rock that is dissolving and full of holes. Our drinking water lies in spaces found in that rock. It's been said that living on this kind of landscape is like living on Swiss cheese.
- Introductory panel to "Karst, a Special Landscape that needs Special Care"

January 8, 2001: The Southeast Minnesota Water Resources Board unveils a traveling exhibit of this area's unique karst landscape and its relationship to water quality. The exhibit was developed by the Science Museum of Minnesota and will be at Eagle Bluff Environmental Learning Center until February 25.

Karst is a type of landscape where rocks are soluble, fractured and lie close to the surface creating direct connections between surface and ground water. We are about to learn the geological history of this landscape and how karst features such as springs, trout streams and caves provide a wide variety of habitats and draw sightseers, birdwatchers and fishermen to the area. We will also learn how this terrain, with its ubiquitous sinkholes, creates a nightmare of potential pollution problems for water resources. The exhibit has something for everyone, including games, videos and a large black trunk full of materials for classroom use.

Commissioner Dick Cummings, Vice-Chairperson, SE Mn Water Resources Board and Bea Hoffmann, Executive Director, SE Mn Water Resources Board welcome visitors and introduce the design team. Donna Rasmussen, Fillmore County Water Plan Coordinator, dons her "Queen of Sinkholes" crown and introduces Fillmore County as the karst capitol of the upper Mississippi valley.

Speaker Jeff Green, Regional Ground Water Specialist, Minnesota Department of Natural Resources (DNR), says karst used to be a problem no one wanted to talk about. We've come a long way over the years; in 1995, the University of Minnesota published the Geologic Atlas of Fillmore County; the mapping of karst in Goodhue, Mower and Wabasha Counties is now underway; the Minnesota DNR recently purchased property rich in karst features near Cherry Grove as a scientific and natural area; and sinkholes are no longer used as dumps. Green says all of this has come about through the cooperative efforts of concerned citizens and local, county and state agencies.

Dr. Calvin Alexander, University of Minnesota Department of Geology and Geophysics, says, "Karst is a state of mind." In slides, he shows us cross-sections of limestone rock, its many vertical fractures and brownish areas stained by water. As water slowly dissolves this rock, its fractures increase in size. When they are large enough to walk through, they are called caves. Fillmore County has hundreds of caves. Mystery Cave, part of Forestville State Park, is the longest cave in the state and Niagara Cave near Harmony extends through three rock formations and has a large waterfall.

We see slides of area sinkholes, which are closed depressions that provide connections between surface and ground waters. Fillmore County probably contains more than 10,000 sinkholes. They form where water-borne sediment sinks or subsides into fractures in the underlying bedrock resulting in erosion of the subsurface. If the erosion is slow, a subsidence sinkhole forms. If the erosion is rapid, the subsurface void can fail suddenly and a catastrophic sinkhole appears. Both types can damage buildings, roads and agricultural property. Facilities such as manure lagoons and sewage ponds require extraordinary precautions if constructed in sinkhole areas due to the risk for contamination if the
facility fails and its contents enter the environment.

Karst systems are dynamic. As they evolve, our understanding and the terminology we use also evolves. They are more complicated than previously thought and there is still much to learn, which presents a challenge to legislators, local officials and citizens because regulations must change as our understanding changes.

Following Dr. Alexander's presentation, Jim Heintzman, Designer, Science Museum of Minnesota, invites us to view demonstrations of materials and activities for classroom use in the Karst Learning Trunk; Mark Dahlager, Project Manager, invites us to tour the exhibit; and Donna Rasmussen serves up pieces of karst correct cake, representing the land surface and layers of Galena limestone, Decorah Shale, and St. Peter Sandstone.

The introduction to the exhibit depicts a cross-section of limestone bedrock. We can hear water dripping and wind blowing through spaces in this rock. A nearby video presents in-depth information on sinkholes, caves, ground water and Minnesota geology.

At the next station, we go back 500 million years to the Paleozoic Era when shallow seas covered most of the state providing basins for the deposit of minerals and shells of marine organisms that eventually became layers of sedimentary rocks: sandstone, which acts like a sponge; shale, which is especially rich in fossils and forms a barrier between water-bearing layers of rock; limestone and dolostone, which are soluble and fractured. The layers of rock carry the names of areas in which they were first discovered. We see examples of Galena limestone, Jordan sandstone and Decorah shale.

A large illustration of a karst landscape depicts the land surface, the underlying rock and various land surface uses. The object for the viewer is to discover safe and potentially unsafe land management practices.

Near this station is a game in which the object is to manipulate a drop of water, represented by a small ball, through a maze without letting it fall into any pollution holes.

Where is Karst Country? This station tells us karst is present in all nine counties of southeastern Minnesota; twenty percent of the land surface in the United States; and ten percent of the surface of the earth. One out of every four persons worldwide lives in a karst terrain.

Here, the visitor can place over a lighted table any combination of map transparencies that depict such information as the locations of karst features, layers of rock formations and areas of high ground water sensitivities and sinkhole probabilities. Here, I find Dr. Alexander,
who graciously answers my questions about surface features in a karst terrain. He explains that not all karst looks like southeast Minnesota; the entire state of Florida has a karst terrain with abundant springs bubbling up from a flat landscape; China has karst towers; and some entire karst landscapes are in one large sinkhole.

Dr. Alexander also explains theories regarding the impact of the ice ages on our terrain. He says the traditional "Driftless Area" (area without glacial deposits) included southeastern Minnesota, southwestern Wisconsin, northeastern Iowa and a small part of northwestern Illinois, but geologists now know that only southwestern Wisconsin and possibly a small sliver of Minnesota escaped all the glaciations. Although the term "Driftless Area" continues in common usage, geologists no longer use it as a scientific term to describe our region.

As the ice ad-vanced and receded, it tore up the underlying rock, carried it on with the ice and eventually deposited it as glacial drift or till. Because all of the traditional Driftless Area and some additional parts of southeastern Minnesota escaped the most recent glaciations, the sedimentary rocks in this region remain close to the surface and mostly intact. Sedimentary rock is present elsewhere, but if it is covered by over fifty feet of glacial till, it is not considered karst terrain.

Ground Water Contamination-Everyone Pays: This section contains a photo of a house that barely missed falling into a catastrophic sinkhole. It also contains an album of newspaper clippings reporting contaminati

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