When venturing into the backcountry, answering these two questions is essential when assessing a slope to ride:
Is the terrain capable of producing an avalanche?
-and-
Can the snow slide?
Avalanches happen when four ingredients are present: a slab, a weak layer, a trigger and a slope steep enough to slide. A key problem when assessing slope angle is that most slopes have varying degrees of steepness. It is critical for riders to assess slope angle frequently.
Winter is in the rearview mirror and spring is gaining momentum but we cannot forget about avalanches. As the seasons change so do the types of avalanches. There are two ways to trigger avalanches: stress the snowpack or weaken it. Dry slab avalanches are common in winter and occur when too much weight (stress) is added to the snowpack. Under a heavy load of new snow, windblown snow or skiers, layers collapse and avalanche from this added stress. In spring the snowpack loses strength and weakens when melting water breaks down snow crystals and provides lubrication between layers. Some types of layers are more prone to this type of weakening and this season the western US has one of the worst: depth hoar.
I would love to know how many sets of tracks were wiped out in Sunday’s avalanche of the Football Field on Saddle Peak. If you carved a set consider yourself lucky. I’m going to guess that not many snowpits were dug and that the only form of stability assessment folks leaned on were that others had skied it beforehand. This was not smart. The avalanche broke during early morning avalanche control on the boundary of Bridger Bowl. An explosive was placed in-bounds, but the avalanche ripped out-of-bounds. Why?
Published in CBU November Newsletter
The day dawns cold and clear with a foot of fresh snow and the promise of incredible powder riding. At the trailhead, the surrounding landscape sparkles like a field of diamonds and the anticipation of a magical day in the mountains builds.
Sled covers are hastily removed and the machines are fired up - the smell of exhaust fills the air. Feeling confident about preparations, members of the group do a quick gear check and then hop on their machines, pinning their throttles towards the backcountry and a day of powder riding.
The GNFAC is looking for an intern for the 2022-'23 winter season. Application deadline is April 22, 2022.
Published in the February 2015 issue of The Avalanche Review.
The Class
Introducing the GNFAC’s New Website!
New look. New feel.
Greetings from the GNFAC.
We just launched our new website today and hope you find it easier to navigate and use. There are two major changes:
1. The site is mobile friendly.
Presented at the 2014 ISSW
In recent years, the propagation saw test (PST) gained popularity for both avalanche professionals and backcountry recreationalists. A limiting factor of the PST is the additional time required to isolate a column on the sidewall of the snowpit. Since I often have limited time to dig multiple pits during a work day, this past season I examined the effectiveness of conducting cross-slope PSTs (CPST). The CPST is simply a PST done across, rather than up, the slope. It is more efficient than the PST, particularly after conducting an extended column test (ECT).
