Spelunking Through The Heart Of Door County

By Roger Kuhns

The thought of crawling under the bed to retrieve a lost sock, or reaching under a couch to capture a coin that has rolled out of reach is enough to deter many people from squeezing into dark, tight, gritty places. But crawling under the earth – through the heart of Door County - where it is always dark, tight and muddy is a passionate hobby for a number of local residents. This is the hobby of caving, also known as spelunking.

Caves in the county are generally small compared to famous ones like Carlsbad Caverns. Also, the Peninsula’s caves are typically partially filled with sediment washed in from the surface, The caves follow zig-zag patterns of rock fractures, a characteristic that can be seen along the peninsula’s shoreline, such as at Cave Point south of Jacksonport, and along the Niagara Escarpment on the west side of the Peninsula.

Horse Shoe Bay Cave's underground river.

Every year spelunker, volunteer fireman and naturalist Bob Bultman and myself take my Clearing geology class in to the caves. Bultman is a lanky athletic caver and can squeeze through tight spots, only to look back at those in tow and grin encouragement. It’s a situation that encourages you to slim down before a day of caving. But all ages have ventured into the caves, including an 80-year-old couple who had never been underground before. The steady cavers in Door County – the ones that “tunnel dream” – are Bultman, John Kellner, Gary Soule, Buzz Davis, George Zachariasen, and Bob ‘Nuke’ Thompson…and now Christine Nesheim.

Soda straw stalactite in Horse Shoe Bay Cave

Caves in Door County are part of a regional geologic environment called “karst” that has formed in the Niagara Dolomite. The dolomite was laid down in a salty sea during the Silurian Period 325 million years ago. Born of water, the dolomite seabed was uplifted by tectonic forces and washed again by water sourced from melting glaciers 9,500 years ago. That water now fills the Great Lakes. The karst formed over tens of millions of years as rain and groundwater moved through the water-soluble dolomite, dissolving out fractures and creating open spaces. Karst is identifiable by the open fractures and holes in the bedrock, many creating depressions in the earth from underground collapse. Some of these depressions, or “sink holes” are so big that you could drive a truck into them. As more and more rock dissolved away, the open spaces grew large enough and connected enough to be considered caves.

The big first room in Horse Shoe Bay Cave

A cave is called a cave when it is big enough for a person to crawl through, but there are countless miles of smaller spaces that meander through the rock. The Peninsula’s bedrock is so full of holes it is as though we are living on a block of Swiss cheese. With this much porosity in the rocks underfoot, the water can flow relatively freely from the surface into the bedrock. This open communication of surface and groundwater means that the potential for contamination of our wells from surface sources is always a problem in the peninsula.

A stratigraphic cross sectional representation of the Niagara Dolomite and other units in Door County. Cave formations are mainly in the dolomite formations (Figure drawn by R.Kuhns)

On one recent adventure Bob Bultman, Gary Soule and myself led experienced and novice cavers through one of the county’s wetter and tighter caves. The trip was a reminder to some and a lesson to others that caving is not to be taken lightly… literally. Some forgot their extra flashlights. For a brief moment they learned what complete darkness is like. Others were reminded that the ambient 48 to 50 degrees F temperatures in the cave means a person can get cold rather quickly, especially while crawling through mud and water. The water in one Egg Harbor area cave was over our elbows while crawling through tight spots. One section of the cave, called the “duck- under” required the more adventurous to dip their bodies underwater, with just enough air space to keep most of one’s head between the water and the low cave ceiling, and then crawl through and out the other side in to a slightly bigger space. On the first trip the water level in the duck-under rose a couple of inches because of rain the day before, and reminded everyone that a cave is a dynamic environment that responds to surface weather conditions.

Thin soil in Door County means groundwater contamination through the Karst terrane can occur rapidly.

Many of the Peninsula’s caves are on private property, and persons interested in caving can learn more by contacting the Wisconsin Speleological Society or the author. Never go into a cave alone, and when caving always check the weather (some caves fill up when it rains), bring an extra light, a compass, food, and notify a friend where you are going and when you expect to return.

Dr. Kuhns is a geologist, ecologist, an experienced caver and writer working throughout the world. He is currently employed by Applied Ecological Services (roger.kuhns@appliedeco.com) working on the protection of water resources in the Great Lakes region and restoration of Canada’s boreal forest. Every year he teaches a field- oriented geology-ecology class at The Clearing in Ellison Bay. Roger lives in Egg Harbor.