A 12-minute catastrophe
At 5:09 AM on December 14, 2005, a section of the upper reservoir at the Taum Sauk Pumped Storage Power Station failed. A combination of design flaws and malfunctioning sensors led to the reservoir overfilling. Water poured over a 900-foot section of the parapet wall, rapidly eroding the rockfill embankment beneath. Within minutes, the wall collapsed, unleashing approximately 1.3 billion gallons of water down the side of Proffit Mountain. The entire reservoir emptied in about 12 minutes, creating a flood with an estimated peak flow of 289,000 cubic feet per second.
The deluge descended with incredible force, sending a 20-foot-high wave of water, rock, and uprooted trees toward the East Fork of the Black River and into Johnson's Shut-Ins State Park. The flood scoured a path 2.6 km long, up to 240 meters wide, and 6 meters deep, stripping away all soil and vegetation down to the ancient bedrock. This newly carved canyon exposed Proterozoic-era rocks for the first time in over a billion years.
An accidental experiment
The bedrock of Proffit Mountain is part of the St. Francois Mountains, a range of Precambrian igneous rocks formed by volcanic activity around 1.48 billion years ago. The exposed rock is primarily Taum Sauk Rhyolite, a type of reddish ash-flow tuff. The catastrophic flood provided geomorphologists with an opportunity to study high-energy flood erosion on hard, crystalline bedrock.
The event is a small-scale analogue for ancient megafloods, such as the Missoula Floods that sculpted the Channeled Scablands of Washington State. Scientists studying the Taum Sauk scour channel can observe freshly-cut erosional features and directly measure how they were formed. The flood demonstrated that geological features like deep plunge pools, longitudinal grooves, and streamlined bedrock knobs can be created almost instantaneously. This challenges long-held assumptions about gradual erosion, showing that some landscapes can be reshaped not over millennia, but in a matter of minutes.