The Devil’s Kettle is a remarkable natural phenomenon in Minnesota where a river appears to split, creating a persistent geological puzzle for decades. The Brule River, flowing toward Lake Superior, reaches a point where its current is divided by a hard rock outcropping. While approximately half the river flows over a traditional 50-foot waterfall, the other half plunges into a deep, cavernous pothole and seemingly vanishes forever. This visual spectacle has generated a mystery: where does the water go after it disappears into the rock?
The Geological Feature and Its Mystery
The formation is situated in a region characterized by ancient volcanic rock, known as rhyolite. At the split, the water on the western side is captured by a massive, eroded pothole—the Devil’s Kettle—and drops out of sight. The lack of a visible exit point led to widespread speculation that the water was flowing through a vast, unmapped underground channel.
This popular legend was fueled because objects tossed into the kettle never reappeared downstream. Curious visitors and researchers dropped logs, balls, and colored dyes into the churning vortex, but none were recovered. This solidified the idea that the water traveled a great distance through a hidden subterranean river system. Theories suggested the water might flow all the way to Lake Superior or even connect to a distant watershed like the Mississippi River.
Solving the Riddle: Where the Water Goes
Despite the enduring legend, the water does not defy physics by flowing into a distant underground cavern. The region’s geological structure, composed of hard rhyolite, is not conducive to forming the large underground passages found in softer rock like limestone. Instead, the water is contained within a much shorter, submerged passage created by erosion. The pothole itself formed over millennia as swirling water and trapped stones drilled a cylindrical hole into the bedrock.
The mystery was finally clarified through scientific investigation, beginning with basic flow measurements in 2016. Hydrologists measured the volume of the river above the split and found it to be nearly identical to the volume measured downstream below the main falls. This initial data strongly suggested that the water was simply rejoining the main flow just out of sight.
To provide definitive proof, a team conducted a dye tracing experiment in 2017. They poured a fluorescent, biodegradable dye into the Kettle and monitored the downstream area for its reappearance. The dye quickly resurfaced in the main plunge pool below the visible waterfall, confirming a short, submerged connection between the pothole and the river channel immediately downstream. This short path is likely a crack or series of fissures within the rhyolite widened by continuous water pressure and erosion.
The reason objects like logs and balls never surface is attributed to the powerful hydrodynamics of the pothole itself. The water creates an immensely strong recirculating current within the deep plunge pool. This vortex acts like a giant blender, grinding down or holding lighter material until it is disintegrated or trapped in the fracture system. Unlike large objects, the dye molecules were small enough to pass through the short, submerged channel and quickly re-enter the river.
Visiting the Devil’s Kettle
The Devil’s Kettle is located within Judge C. R. Magney State Park, situated on the North Shore of Lake Superior in Minnesota. Visitors can access the feature via a moderately challenging hiking trail that follows the Brule River. The route is about two miles round-trip and includes approximately 100 to 200 steps to reach the viewing area.
The trail offers several vantage points, culminating at a platform that provides a clear view of the water splitting and disappearing into the rock. The best time to visit is during the spring thaw or after heavy rains when the water flow is highest, maximizing the dramatic effect of the falls. Visitors must obtain a state park vehicle permit and are reminded to remain on marked trails to protect the natural environment.