Geologic hazards of the Bighorn River Floodplain: Preemptive rock attack

The rest of this series will propose best solutions to dealing with the geologic hazards of the Bighorn River Floodplain. A previous column described the geologic hazards caused by the Wind River Canyon rockslides. These rockslides are a threat to motorists, trains and even the town of Thermopolis. The canyon closures and the vehicle and train wrecks are obvious reminders of the dynamic force of gravity at work on the walls of the canyon, often aided by precipitation and train vibration. A more catastrophic event would be a large-scale landslide triggered by a combination of heavy precipitation and/or a seismic event. The Wind River could be dammed up by the obstruction of rock and associated debris causing a large build-up of water referred to as a landslide lake. When this dam is finally breached, it could release a tidal wave of water which would threaten the lower-lying areas of Thermopolis.

A “preemptive rock attack” is similar in concept to the snow avalanche control measures taken in the Colorado portion of the Rocky Mountains. Specially-trained crews, armed with an artillery piece, shoot explosive shells into pending avalanches. The result is an intentionally-triggered avalanche under controlled conditions. No one is endangered and the threat is removed.

This concept of controlled release of the potential energy stored in the unstable material can be applied to our situation in the Wind River Canyon. Rocks which are precariously perched above the roadway can be brought down and removed. Unstable rocks which are too large to be economically removed should be secured with rock bolts. Areas bordered by large volumes of dirt and smaller rocks, the result of road cuts through alluvial cones, can be netted or walled-in to prevent falling upon the road. This preventative measure allows for periodic maintenance by removal of captured debris.

A geologic engineering study of the stability of the canyon walls can discover if there may be specific situations where a large landslide would have the potential to dam-up the river. If such a situation exists, it is a geologic hazard that needs to be stabilized or removed. A limited version of this concept has been recently applied to Windy Point in the Canyon. A company specialized in handling these unstable rocks has reduced the threat in a specific area. A preemptive rock attack is possible with a concerned citizenry, enlightened geologic engineering and, of course, money.

Please attend the meeting for citizens concerned about planning for potential disasters to be held at 5:30 pm on June 14 at Big Horn Federal.