Geologists investigate 'slow-moving landslide' developing in Wyoming's Bighorn Mountains

A massive fissure that has mysteriously appeared on the flanks of the Bighorn Mountains in Wyoming is a slow-moving landslide possibly triggered by excessive precipitation combined with moisture from a nearby spring, a state geologist said on Friday.

The mass geologic movement in the remote area where no people or property are directly at risk came to light last week when commercial hunters in Wyoming discovered it and posted photographs and commentary on their firm's Facebook page, sparking a flurry of online interest.

The hunters from SNS Outfitters and Guides said in a posting that a device used to measure distance for hunting purposes suggested the fissure was 750 yards (meters) long and 50 yards (meters) wide.

"This giant crack in the earth appeared in the last two weeks on a ranch we hunt in the Bighorn Mountains. Everyone here is calling it 'the gash' It's a really incredible site," the hunters said in a posting last Friday.

Seth Wittke, division manager of the Wyoming State Geological Survey said the so-called "mass wasting event" was relatively large in size even for a state that has mapped tens of thousands of landslides in the past century.

"It's a medium-to-large-sized event by Wyoming standards," he said. Most of those happen in remote areas and do not directly threaten lives or property, he added.

Wittke said the significant shifting seen in the Bighorns south of the tiny community of Tensleep, Wyoming, was likely tied to moisture acting as a lubricant in the slumping of layers of rock and soil already weakened by a freeze-thaw cycle that routinely happens in winter and spring in the Rocky Mountains.

Although the slide does not appear to pose any known imminent threats, it could cause harm if it were to catastrophically fail at a time people were in the vicinity, Wittke said.

"Each landslide is unique. You can't say whether this one will be the one to fail but the potential does exist," he said.

(Reporting by Laura Zuckerman; Editing by Dan Whitcomb and Sandra Maler)