Mountain Safety

Tip-Toeing into the storm to get a snow report.

Red Flags is a Jones Avalanche Awarness Month series detailing Live-From-The-Field stories about five of th emost common signs of Avalanche danger - The red flags. Second up in the series we have a behind-the-scenes look at a Tahoestorm day when Jeremy Jones and the crew turned around on a tour when they observed shooting cracks in the snowpack.

Words and Photos by Seth Lightcap

It was the third day of a notably epic powder cycle in Tahoe (See “Deep Week” from DEEPER). A massive cold front had parked itself over the Sierra and it just kept snowing and snowing and snowing. The storm was forecasted to lull during the day so Jeremy Jones, Forrest Shearer, Ryland Bell, Chris Edmands and I went on a backcountry tour in a low angle tree zone to go check out how the snow was stacking up. Ryland Bell remembers what went down on the tour well:

“We were breaking trail in the woods and all of a sudden we hit a certain elevation where the wind had deposited a much thicker and denser surface layer. As soon as we crossed that elevation line we started seeing long ‘shooting cracks’ fracturing through the snow ahead of us as we broke trail. One step I took fractured a 30 foot long pocket that was a foot deep.

Seeing the shooting cracks stopped us immediately. We were done going up. The plan all along had been to stay low and not ride steep terrain because it was still storming and we had seen other red flags, but the shooting cracks were an obvious sign that it was time to retreat.“ – Ryland Bell

Shooting cracks in Tahoe. Photo by Sierra Avalanche Center.

Shooting Cracks are a major avalanche danger red flag. When you see a shooting crack it is a tell-tale sign that the surface snow layer is unstable and sitting on top of a weak layer. The shooting crack shows that the surface layer has already begun to fracture on the weak layer. Usually the shooting cracks are accompanied by a ‘whumpf’ sound that occurs as the cracks are triggered. Weak layers in the snow pack tend to have a lot of air space between the snow grains. When the weak layer fails under the compression of the upper layer, the ‘whumpf’ is the sound of air getting pushed out of the weak layer.

Jeremy starts the compression test with ten taps from the wrist, nothing moved until two taps from the elbow.

At the elevation that we saw the shooting cracks, Jeremy Jones dug a pit. The compression test results were CT12 @ 25 cm (Q2/3). The shear surface was a rough crust and the slab didn’t break off completely clean. We were dealing with an increasingly unstable wind slab that didn’t have quite enough energy to slide on the pitch angle we were at, but could be substantially more dangerous on steeper terrain.

Having seen three of five red flags (wind loading, new snow, shooting cracks) there was no doubt in anyone’s mind but to turn around. We rode down our skin track to a low consequence zone and shot a few mellow pow turns. By paying attention to the red flags we had immediately sensed when the danger increased and made the call to turn around before getting ourselves into trouble.

Just enough pitch to open the door to the white room for Jeremy Jones.

Low angle doesn’t have to mean low fun. Ryland Bell exits a Blower Cutback.

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Author
Seth Lightcap
Category
Mountain Safety
Published on
18 December 2012

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