Mountain Safety Note
- Avalanche Safety Basics -
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This reminder about avalanche safety was sent to the mailing list of the Oregon State University Mountain Club before a weekend trip which was to take place during a period of high avalanche danger. It's good advice at any time and worth refreshing ourselves on from time to time.
Date: Thu, 15 Jan 1998
Remember that it is possible to have a fun and safe backcountry experience during any hazard level, even a warning. Your keys to this are terrain and using safe travel protocols. Routefinding which avoids avalanche terrain avoids the problem and traveling safely covers the residual risk.
Remember: Slope angle is everything! Slopes under 25 essentially never avalanche, and those in the 25-30 degree range rarely slide. The most dangerous range is 35-40 degrees. Your key to finding safe terrain in the backcountry when the snowpack and weather factors are against you is slope angle - carry an inclinometer (slope meter). This will let you have a great day without worrying too much about stability.
Even in generally low angle terrain watch for terrain traps. Several of this seasons fatalities involved terrain traps, including the four teens killed near Canmore. Terrain traps include areas where a small slide can have major results (like cliff bands below) and gullies where a small slope can deposit deep debris in the bottom. (The short steep slope near the start of Todd Lake road was the sight of Oregon's last avalanche fatality.)
Watch the vegetation for clues that you are in avalanche terrain - slide alder, the existence of flag trees, etc.
Slopes with enough trees have a better anchored snowpack and tend to be safer.
Most avalanches occur during or shortly after a significant loading of new snow. The underlying snowpack will adjust to the new load over time, but can suffer elastic failure when loaded too quickly. The faster the snow falls and the greater its water content the closer the snowpack will be to being critically loaded. Today's avalanche bulletin mentions 8 feet of snow in the last 11 days, but does not say where this was measured.
Wet snow or rain loads the snowpack more rapidly, and rain has other bad effects as well. Rain isn't much fun to be out in anyway!
Wind causes significant loading with or without new snowfall. Watch out for wind slabs near ridge tops and in gullies subject to cross loading.
This is the most complicated factor to assess. Strength and stability tests must be done on representative slopes, and this is often difficult to do safely.
Watch for signs of a buried layer which is weak in compression, such as the snow going "whumpf" under you. Compressive failures propagate a long way with ease, and in these conditions you can trigger a slide from below in the runout zone. You can also trigger a treed slope - trust me on this, I know! Most of the western US east of the Cascades has conditions like this, but it is much less common in the Cascades. We did have a slope collapse under us at Mt Bachelor during a ski patrol advanced class last year. (It was a great chance to look for the weak layer and do Rutschblock tests.)
This is really the source of most involvements. Thinking about human factors such as group dynamics and decision making increases safety overall, not only from avalanches.
Plenty more on this topic ... give it some thought! And share your thoughts as well.
Safe Traveling Protocols
There are certain travel procedures which should be second nature. They should be used as a matter of habit regardless of hazard level. Some of them are:
This is brief and very basic, but it is enough to keep out of trouble. The Outdoor Rec Center has at least one avalanche safety video - "A Question of Balance". It is 30 min and well done. If you are going into the backcountry this weekend it would be a good refresher.
Also, avalanche beacons can be rented in Bend. Put your own brand new batteries in though, and make sure you know how to use the thing. It's not intuitive. Didn't Dale say he was going to practice? If so, join him.
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