The water slides in the Wisconsin Dells today are a strange, accidental metaphor for the area's geological history.
An ice dam that broke towards the end of the last Ice Age sent water from a glacial lake down the Wisconsin River, carving the fanatical sandstone cliffs that distinguish the Dells today.
That's one of many reasons why geologist Marcia Bjornerus sees beyond the Wisconsin Dells' water parks, tacky shirt shops, and salt water taffy.
Bjornerud is a professor of geology at Lawrence University in Appleton, and recently wrote about the amazing natural history of the Wisconsin Dells for The New Yorker’s Elements blog.
The word 'dells' is unique to Wisconsin. It "usually means a deep gorge that has unusually rounded, sculpted outcrops of rock," she says.
These sandstone rocks themselves were laid down when Wisconsin looked very different. "They are almost 500 million years old, and the very clean quartz nature of these sands indicate that there were probably a beautiful wave-washed beach back then, when Wisconsin was south of the Equator and the global climate was a lot warmer," Bjornerud says.
Much of this geological activity took place when Wisconsin was at a much different latitude. Bjornerud says the continent of North America actually looked entirely different too. "We were on the coast and we wouldn't really recognize the shape of the continent at all," she says. "The west part of the U.S. and the east coast hadn't even been formed at that point."
So, she says, the Wisconsin Dells' sandstone cliffs and islands of today are a snapshot of what the world looked like eons ago.
"From north to south and east to west, we have rocks that range from 2.7 billion years old to glacial deposits that formed yesterday, geologically speaking, and that spans more time than the whole of the Grand Canyon."
Bjornerud says most impressive was the speed with which the cliffs were formed. "Most geological phenomena take place over very long periods of time," she says. "There's pretty strong consensus now that the dells themselves, the carving of those outcrops, happened perhaps in a couple of days or week late in the Ice Age."
Depending on where you look, you are getting a glimpse into very different chapters of a long, long story, she says. "At the Dells, we are seeing a time when we were in a tropical, shallow sea environment."
What makes the sand unique in this area is that it is almost pure quartz and the grains are very round and very uniform in size. "It is beautiful sand, you can imagine an ancient beach - just white, golden and lovely," shes says.
"Wisconsin has a phenomenally long geologic story to tell, and I think we have really only scratched the surface in many cases," Bjornerud says."I like people to realize that there are amazing things to be explored in this part of the world."
