Technical information, news, research, and opinion on avalanches, snow safety, and winter backcountry travel.

Tuesday, November 18, 2014

6 Signs of Exposure

Where am I to go, now that I've gone too far? — Golden Earring

Let's talk about terrain selection for a few minutes. A few years ago I wrote a rather long article on terrain selection, which I followed up with another article that explained the statistical basis for the model. I don't think anyone would argue about the importance of terrain selection, but the simple model of evaluating slope angles isn't quite enough.

With that in mind, I'm going to write a simpler post that discusses the six universal signals of exposure. The benefits of the six universal signals of exposure is that they're easy to use ( regardless of experience ) and they can easily be integrated into trip planning. This means you can evaluate exposure before you set foot on the snow.

The Model
LOCALE. A model for analysing exposure that gives you holistic information about exposure to avalanches.

  • Is line-of-sight limited?
  • Do local terrain features obstruct your line-of-sight to terrain above or below?
  • Is your uphill view blocked by rocks or trees?
  • Can you see all the terrain above and below or only some of it?
  • Pay attention and double-check your decisions when line-of-sight is limited for any reason.
  • Limitations to line-of-sight can reduce your reaction time to zero. ( I personally feel like this is one of the most important, and overlooked, elements of terrain selection. )
  • Is the terrain open enough to produce small, medium, or large avalanches?
  • Are there open breaks in the forest that allow snow to travel unobstructed to your location?
  • How much open terrain is present and where is the open terrain relative to your location?
  • Large quantities of snow can accumulate in open areas near mountain tops before an avalanche and in valley bottoms after an avalanche.
  • Is the terrain confined relative to the size or speed of an avalanche of any size?
  • Could a large, fast-moving avalanche overrun the valley floor?
  • Are you in a gully where escape from a small but fast-moving avalanche could prove impossible?
  • Small avalanches form deep deposits in confined terrain, such as hollows or depressions, where snow can accumulate.
  • Estimate your reaction time before something goes wrong and double-check your decisions if reaction time is short.
  • Reaction time is a very important part of your margin of safety because it can tell you a lot about the true degree of exposure for where you plan to travel.
  • Has snow accumulated above or below?
  • Avalanches often start where snow accumulates, and then run downhill where they deposit snow on the valley floor.
  • Are there obstacles above or below?
  • This includes cliffs, crevasses, rocks, and trees.
  • Obstacles above may block your line-of-sight, inducing hazard blindness, and can cause traumatic injuries during any phase of an avalanche.
  • On the other hand, obstacles can block or redirect flowing snow and may offer protection at your current location.
  • Is the terrain steeper than 30 degrees?
  • Avalanches start and rapidly accelerate on steep terrain.
  • Steep terrain produces fast-moving avalanches that can release above you and travel toward your location.
  • If you trigger an avalanche on steep terrain, you may be unable to escape from the flowing snow.
  • Steep terrain can limit your line-of-sight, and indicate locations suitable for sluffs, cornice drops, serac fall, or rock fall—all of which can start avalanches above or around you.

No comments:

Post a Comment