NEWS: On 23 October 2015, the SNS Outfitter & Guides Facebook page uploaded images of a “giant crack” that had appeared on the southern end of the Big Horn Mountains in Wyoming earlier that month:
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 sight.
The hunting outfit uploaded additional photographs a few days later along with an explanation for the “gash” provided by an engineer:
Since so many people have commented and asked questions, we wanted to post an update with a little more information. An engineer from Riverton, WY came out to shed a little light on this giant crack in the earth. Apparently, a wet spring lubricated across a cap rock. Then, a small spring on either side caused the bottom to slide out. He estimated 15 to 20 million yards of movement. By range finder, an estimate is 750 yards long and about 50 yards wide.
The “gash” in the Big Horn Mountains is on private property and as of 29 October 2015 it hadn’t been examined by experts other than the unnamed engineer mentioned above. But Seth Wittke, Wyoming Geological Survey’s manager of groundwater and geologic hazards and mapping, told the Powell Tribune that the “gash” was likely caused by a slow-moving landslide:
The new formation is likely the result of a slow-moving landslide, said the Wyoming Geological Survey’s manager of groundwater and geologic hazards and mapping, Seth Wittke. Landslides can move at catastrophic speeds, such as what is observed in Washington state, while others can be much slower
The size of this type of opening can vary depending on the size of the hill and the stability of the land, he said.
“A number of things trigger them, moisture in the subsurface which causes weakness in soil or geology, and any process that would weaken the bedrock or unstabilize it somehow,” Wittke said.
While the Wyoming Geological Survey has not been able to get on the ground near the gash yet, the group’s public information specialist noted that formations such as the one shown in the above-displayed photographs are not uncommon:
“All we have seen is pictures since it is on private land,” said Wyoming Geological Survey’s public information specialist Chamois Andersen. “It’s hard to assess without someone on the ground looking at it.”
Based on prior mapping and what’s visible in the pictures, “the gash” is likely a slump, slide or detachment, Andersen said. But, without an on-the-ground investigation, it’s difficult to determine.
“There is some speculation on the web, and with our folks too, that an early, wet, spring and summer had a lot to do with it,” Andersen said. “It is not uncommon to have slides like that.”
The Wyoming Geological Survey also posted a message concerning “The Crack” at the southern end of the Big Horn Mountains:
The WSGS is aware of the apparent active landslide in the southern end of the Big Horn Mountains, Wyo. “The Crack,” as it has been called, looks to be a relatively large yet slow moving event. Based on anecdotal evidence from postings on Facebook and other social media sites, it appears that this event may be due to groundwater creating weakness in an unstable hillside. WSGS geologists have not visited the site so we do not have any first-hand information about this event. We would like to remind the public that active landslides are typically unsafe. Please keep your distance from any active landslide in case the slope catastrophically fails. We would like to encourage the public to report any landslides they see in Wyoming to WSGS “Report a Landslide,” at http://www.wsgs.wyo.gov/hazards/report-landslide.