Half the Brule River vanishes into a pothole and never reappears. Despite dumping dye and GPS trackers; scientists cannot find where the water goes.
August Schwerdfeger, CC BY 4.0, via Wikimedia Commons
A Geological Puzzle
In Judge C. R. Magney State Park, the Brule River is a curious feature. At a specific point, the river splits around a large outcrop of rhyolite, a type of volcanic rock. The eastern channel cascades down a 50-foot (15 m) waterfall in a conventional manner. The western channel, however, drops 10 feet into a deep pothole known as the Devil's Kettle and seemingly vanishes. For decades, this geological feature fueled speculation. Observers tossed in objects like logs and ping pong balls, but none were ever seen resurfacing in the lower parts of the river. Theories suggested the water traveled through a vast underground cave system, possibly emerging under Lake Superior or even connecting to river systems in Canada.
The geology of the area made these theories unlikely. The bedrock is primarily hard rhyolite and basalt, formed from lava flows around 1.1 billion years ago during the formation of the Midcontinent Rift System. This dense volcanic rock does not easily form the large caverns and channels characteristic of karst landscapes, which typically develop in softer, soluble rocks like limestone. The mystery of the disappearing water persisted, preventing a direct geological explanation.
Solving the Vanishing River
The solution to the puzzle of the Devil's Kettle was confirmed by the Minnesota Department of Natural Resources (DNR) through careful hydrological measurements. In the fall of 2016, hydrologists measured the volume of water flowing in the Brule River at two points. Upstream from the split, the flow rate was 123 cubic feet per second (3.48 cubic meters per second). Several hundred feet downstream from where the two channels should have rejoined, they measured the flow again and found it to be 121 cubic feet per second (3.43 cubic meters per second).
In stream gauging, these two measurements are considered essentially identical, accounting for the tolerances of the equipment. The data showed that no water was actually being lost from the river system. The water that enters the Devil's Kettle must therefore re-enter the main channel of the Brule River a short distance downstream. The long-held belief that items disappeared forever is explained by the immense power of the water inside the pothole. The churning, recirculating currents are powerful enough to pulverize and disintegrate objects, holding them below the surface until they eventually resurface much further downstream, likely unnoticed. The "mystery" was officially declared solved in 2017, ending folklore with fluid dynamics.
💡Fun Facts
The park was named in 1963 for Judge C. R. Magney, who was instrumental in establishing 11 state parks along the North Shore.
The hard volcanic rock that forms the kettle is part of the Brule River rhyolite flow, which is estimated to be up to 770 feet thick.
Despite the conclusive flow-rate data, a planned follow-up study to pour biodegradable dye into the kettle was deemed unnecessary by the DNR.
Objects thrown into the kettle were likely trapped and pulverized by the powerful underwater currents, which act like a giant blender.
A daily or annual Minnesota State Parks vehicle permit is required. A daily permit is $7.
Accessibility
The park has some accessible picnic sites and facilities in the campground, but the trails are not paved. The hike to the Devil's Kettle is a strenuous 2-mile round trip with numerous stairs, including a flight of about 200 steps.
