SUGAR CREEK - On Saturday, August15, nearly 60 people gathered at Sugar Creek Bible Camp for Crawford Stewardship Project’s 14th Karst Exploration Event. These annual CSP flagship events pair a scientific presentation with a field trip, each year focusing on a different karst feature such as sinkholes, caves, and this year: springs!
While the Sugar Creek kitchen laid out a diverse spread for lunch, Joe Childs demonstrated CSP's twin groundwater simulators. These plexiglass models, which look similar to an ant farm, are a window to the underground world of our local soil and bedrock.
One model shows sandstones, which serve as our primary local aquifers, while the other shows karstic carbonate bedrocks (limestones & dolomites) — the kind of rock that rainwater slowly dissolves over time, riddling it with cracks, tunnels, and caves — which form much of our local hills.
Water poured in the top of each model behaves very differently, but always looking for a ‘release point,’ whether that be a spring, lake, river, or actively pumping well. In the sandstone model, water is held similar to a sponge, moving in a slow plume, capable of moving down, across, or even drawn upwards by pressure differences. In the karst model, water moves rapidly, piercing downward and horizontally in seemingly chaotic ways through the bedrock.
For our presentation, we heard from Chloé Fandel, a geology professor at Carleton College in Minnesota who has worked on water projects in France, Oregon, Colorado, Arizona, and now here in the Midwest.
Through Carleton Hydrogeology Research, she led a team that spent the last few years studying 320 springs across the four-state Driftless Region: ‘Surveying Springs in the Driftless: A Snapshot of Groundwater Quality in a Geologically Unique Region of the Upper Midwest.’
We learned that 3,348 springs have been officially mapped, and that there is great variety within springs — from dramatic rocky waterfalls to sand-boils to muddy seeps, some flowing in slow trickles or intermittently, and some pumping out 100 cubic feet per second.
Most of the largest springs are in the western portion of the Driftless, coming from the Platteville-Galena limestones. This makes sense, as that limestone is highly permeable, funneling water down until it hits the underlying, impermeable layer of Glenwood shale — which stops downward flow like a waterproof floor, pushing more water out to the surface where the karstic bedrock meets the shale.
By contrast, most springs in Crawford County are smaller, producing a cubic foot per second or less, however, our Prairie du Chien dolomite hills are the geological layer with the greatest number of springs in them. This makes sense too — there's no truly impermeable layer underneath this bedrock to stop water from flowing downward, but as the oldest of the carbonate layers, it's had the most time to develop interconnected fracture networks with outlets that become springs.
This process was demonstrated live, dropping acid onto a piece of dolomite to reproduce the dissolution that naturally occurs — slowly, over hundreds of thousands of years — as mildly acidic rainwater passes through the rock, carving the cracks, caves, and tunnels that shape this landscape and heavily influence how, where, and how fast water flows.
Some excellent local news: while springs often carry somewhat elevated nitrates (a widespread concern for drinking water, largely coming from fertilizers and animal waste) the springs on the Wisconsin side of the Driftless had the best water quality of the whole region! Is it something about how we manage our land here? Differences in the underground geology or surface landscape? These are questions that we hope to help answer in the coming years.
Even the professional geologists in attendance came away having learned something — such as that the average age of the water tested was less than 73 years old. A water sample's ‘age’ is determined through tritium testing, which measures the small amount of naturally occurring radioactive hydrogen in it to figure out when it fell as rain and entered the ground. Because tritium breaks down at a predictable rate, scientists can tell fairly precisely whether water was recharged recently or has been underground for decades or centuries.
As is often the case with studies in our area, what's been surveyed so far only represents a fraction of the possibly tens of thousands of springs actually here (a number that shifts with the water table). But the work of compiling all available surveys and data is invaluable, and the detailed study of these hundreds of springs gives us real insight into the complex above- and below-ground watersheds we live in.
Equipped with new understanding, and ready to enjoy the day, the group was ushered through a tour of three distinct types of springs on a half-mile walk. Even Chloé, who had studied a different spring on the camp before, was impressed that the property hosted hillslope, rheocrene, and limnocrene springs all in one small area of the 660 acre property — each with different lessons to teach us.
We even got to experiment with fluorescein, a bright green dye that's been used safely by hydrologists for decades to trace how water moves underground. It's non-toxic, breaks down naturally in sunlight, and is visible to the naked eye in concentrations as small as a few parts per billion — which is what makes it so useful: a tiny, harmless amount can reveal connections that would otherwise be completely invisible.
Poured into a sinkhole or disappearing stream, it lets researchers trace exactly where that water resurfaces — whether a sinkhole feeds a particular spring, whether a pollution source could reach downstream, or simply how fast and how far water travels underground.
Crawford Stewardship Project hosts Karst Explorations annually, digging into different karst features each year and learning what they have to teach us. Forest Jahnke, who has coordinated these events for over a decade, says the same lesson comes up every time: in karst, everything is connected.
If you’re interested in attending a future exploration, keep an eye on the CSP events page at CrawfordStewardship.org. And if you've got a karst feature on your own property you think could be a fun site for a future event, please reach out to Forest at forest@crawfordstewardship.org.
