Devil's Kettle: A Mysterious Waterfalls

The Devil's Kettle is a puzzling geological phenomenon located inside Judge C. R. Magney State Park in Minnesota, in USA, just off the North Shore of Lake Superior.

As the Brule River makes it way through the park, it drops 800 feet in elevation and creates numerous waterfalls in the process. One of these waterfalls is quite special.
 

About 2.4 km before the river empties into Lake Superior, it gets split in two by a rocky outcrop. The eastern part drops 50 feet below and continues towards Lake Superior.

The western part falls 10 feet into a giant pothole - the Devil's Kettle - and disappears. Nobody knows where the water goes. It is believed there must be an exit point somewhere beneath Lake Superior, but it has never been located.

Over the years, researchers have dropped brightly colored dyes, ping pong balls, and other objects into the Devil's Kettle. So far, none has ever been found.
 

One theory is that the river flows along an underground fault and comes out somewhere under Lake Superior.

This is unlikely, because for this to happen, the fault would have to be precisely oriented towards the lake, and would have to be large enough to allow the flow of half the river.

Even if such a fault exist, it would have likely been clogged over the years as rocks, sand, logs and other materials fell into the kettle. Besides, there is no evidence of such a fault in the area.

Another theory is millions of years ago a lava tube formed when the rocks first solidified.
 

The problem with this theory is that the rock at Devil’s Kettle waterfalls is rhyolite, and lava tubes never form in rhyolite.

Lava tubes form in basalt flowing down the slopes of volcanoes, and the nearest basalt layer to Devil’s Kettle is located much too far underground to be any kind of factor in the mystery.

The existence of a large underground cave is also ruled out because underground caves form in limestone rock, and there are no limestone in the area.