MINNEAPOLIS (WCCO) – If you’ve ever visited Minnesota’s north shore of Lake Superior, you’ve no doubt been inspired by vistas of jagged rock and tumbling waterfalls.
Perhaps, even perplexed by one scene in particular – the Devil’s Kettle.
The attraction inside Judge C.R. Magney State Park near Grand Marais has mystified visitors for decades, where water in the left fork of the Brule River waterfall appears to simply vanish into a large hole in the rock below.
In the summer of 2012, WCCO’s Mike Binkley explored the mystery of Devil’s Kettle for a Finding Minnesota feature. He experimented by tossing a ping pong ball into the cauldron etched with his phone number.
Last we heard, Binkley has yet to receive a call from the person who recovered the ball.
Over the decades, others — including scientists — have tossed in logs and even dye in hopes of tracing the water’s flow. Nothing ever surfaced.
“It gets ground up. It’s a pretty powerful churning,” said retired University of Minnesota professor Calvin Alexander.
Alexander suggests thinking of the kettle as nature’s giant blender. The water is churning around the hole in the rock with such power and force that it essentially shreds whatever material enters the pool.
Still, the questions remain: What happens to the flowing water and where does it exit to the surface water?
“The first thing you do is measure the water and it turns out nobody had ever done that,” Alexander said.
Last fall, he and DNR hydrologist Jeff Green did just that.
What they discovered is that the river’s water volume is nearly identical when measured both above and immediately below the falls. Their observation essentially debunks the myth that the water is taking an alternative route underground to nearby Lake Superior.
To help visualize their observation and measurements and to show the location of where the water is re-entering the Brule River, the scientists plan on pouring a bright green dye into the falls above.
They are betting that it will turn the river water directly below the same color, proving that the exit to the kettle is merely a short distance away.
“It’s cool, it’s neat,” Alexander said. “We now know something we didn’t know before. That’s what turns a scientist on.”
High above Lake Superior and more than a mile inland, the Devil's Kettle waterfall on the Brule River has enchanted onlookers and stoked the curiosity of scientists for decades. The most visited attraction at Judge C.R. Magney State Park near Grand Marais, it has also been the most puzzling. Above the falls, the river splits in two at an outcropping of rhyolite—volcanic rock as hard as granite. The east side of the river plummets 50 feet into a pool, in typical waterfall fashion. But on the west side, the water plunges into a cavernous hole in the rock and vanishes, leaving observers wondering: Where does all that water go?
Over the years, curious onlookers would sometimes toss a stick or another buoyant item into the swirling waters of the pothole to see if it would resurface downstream. Nothing ever did.
Without seeing an obvious resurgence of water, many people have speculated that the water followed an alternate underground path to Lake Superior. Geologists said that wasn't likely. Underground waterways form in softer rock such as limestone, but the geology of the North Shore is anything but soft. Tunnels, or lava tubes, do not form in rhyolite or in the volcanic basalt far beneath the riverbed.
DNR springshed mapping hydrologist Jeff Green and other scientists have long thought that the water that enters Devil's Kettle didn't divert through a hidden channel to the lake, but rather resurfaced in the river downstream. To test this theory, Green asked the DNR's water monitoring and surveys unit to measure the volume of water flowing above and below Devil's Kettle using stream gauging equipment. By comparing the amount of water flowing above the waterfall with the amount of water flowing below the falls, hydrologists could determine if there was a loss of water somewhere between the locations.
In late fall 2016, hydrologists Heather Emerson and Jon Libbey measured water flow above Devil's Kettle at 123 cubic feet per second. Several hundred feet below the waterfall, the water was flowing at 121 cubic feet per second. "In the world of stream gauging, those two numbers are essentially the same and are within the tolerances of the equipment," Green explains. "The readings show no loss of water below the kettle, so it confirms the water is resurging in the stream below it."
Green and Calvin Alexander, a colleague at the University of Minnesota, plan to conduct a dye trace to show where the water resurfaces. In the fall of 2017, during low-water flow, they will pour a vegetable-based dye into the pothole. This fluorescent, biodegradable dye is visible at 10 parts per billion, so the hydrologists will use only a few quarts.
As far as the mysteriously disappearing items, water force and fluid dynamics offer an explanation. Alexander explains, "The plunge pool below the kettle is an unbelievably powerful system of recirculating currents, capable of disintegrating material and holding it under water until it resurfaces at some point downstream." Unlike larger objects, the dye molecules won't be held in Devil's Kettle.
Cheri Zeppelin, DNR information officer