Rockfall

In this still from a video captured by an Exum mountain guide, clients and other climbers watch as a river of rock, soil and water cascade down Garnet Canyon for almost an hour.

When the largest boulder slapped its way down the granite gulch feeding down Disappointment Peak, climbers who watched, mesmerized, hooted and hollered like amped-up animals.

“Oooooooohhhhhhhhhh,” an onlooker screamed into the rainy abyss of lower Garnet Canyon.

“I’ve never seen anything like this!” another climber blurted out.

It was early afternoon Aug. 8, and a group of climbers who had just summited the 13,775-foot Grand Teton were taking shelter from a hailstorm under a rock wall just shy of Petzoldt Caves. And in perfect view, harmlessly off to the side, an incredible volume of earth streamed down the mountain. It kept coming and coming and coming, eyewitnesses say.

A video posted on Facebook documents 4 minutes of the rockfall, but the rare episode of accelerated erosion persisted for much longer. Guide Adam Fabrikant, who was present that early August afternoon, said he, clients and other climbers watched in awe as the river of rock, soil and water cascaded by for at least 40 minutes, and perhaps as long as an hour.

“I had never witnessed anything like that,” Fabrikant said. “The closest thing I’ve seen is avalanches, but this was an avalanche of rock. It behaved more like a mudslide or landslide.”

Short of an on-site examination — which has not occurred — it’s impossible to say what precisely caused thousands of tons of the Tetons to slough down the unnamed Disappointment Peak gulch.

“There was a large amount of water and hail that came down over a short period of time,” Fabrikant said. “That’s what we know with certainty.”

There are theories about what happened, though. Former Exum guide and frequent Tetons traveler Tom Turiano said he knows that area well, and his hunch is that the cause is an “affordable house”-size chunk of chockstone wedged into Disappointment’s Southwest Couloir.

“Over the eons, boulders and scree have built up above it, pushing on it,” Turiano said. “I would imagine during the course of spring and early summer all that gravel backed up behind it would become saturated, and then suddenly it could release.”

Alternatively, he said, the chockstone itself may have released.

“I bet that’s it, but I have no idea,” Turiano said. “I haven’t been up there yet.”

Grand Teton National Park rangers also haven’t made it up to investigate the source and resting place of the sustained rockfall, though there are plans to do so, physical sciences chief Simeon Caskey said. Rockfall in the Tetons is routine, he said, but it’s hard to gauge how common a large-magnitude event like the Aug. 8 high-angle landslide is. Caskey encouraged visitors to report any landslide or rockfall to a Grand Teton visitor center.

Turiano, who has spent decades in the Tetons, said such geology in action is indeed a rarity.

“I’ve watched Teepee Chimney go big, sliding for a minute,” he said. “But I’ve never seen anything like that there, or anywhere else in lower Garnet Canyon.”

Fabrikant was similarly impressed.

“I’m just happy that our whole crew was in a safe location to see it,” he said. “It was a wild event to witness.”

Contact Mike Koshmrl at 732-7067 or env@jhnewsandguide.com.

Mike has reported on the Greater Yellowstone Ecosystem's wildlife, wildlands and the agencies that manage them for 7 years. A native Minnesotan, he arrived in the West to study environmental journalism at the University of Colorado.

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(1) comment

Deirdre O'Mara

https://youtu.be/Kyya7gG8wI4



I'm posting this video with the permission of Adam Fabrikant who's up on the Grand Teton tonight. The video was taken at 2 PM on August 8th. - Tom Bennett


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