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

Tuesday, November 8, 2011

REI Avalanche Safety

If you could read my mind, what a tale my thoughts would tell—Gordon Lightfoot

REI has an interesting feature on avalanche safety. My criticism in a single sentence: it's a disconnected collection of "rules of thumb" punctuated by errors, some of which are significant. It's clear the authors know something about snow safety... but... not quite enough.

From the first page in the series:

During winter, a south–facing slope is more stable than a north–facing one since it has sun exposure to melt and condense the snow. The tempting north–facing slopes that hold all the best powder are also more likely to have unstable layers of ’depth hoar,’ the dry, icy snow that does not stick to the adjacent layers. Since these slopes don't have the benefit of sun to warm and compact the snow over the winter, they tend to be less stable than south–facing slopes.

This is not true. Instability can develop on any slope, at any time during the winter. In fact, The Avalanche Handbook, citing research by Grimsdottir, plainly states that, after accounting for slope use patterns, aspect is a poor predictor of avalanches. You should never use aspect by itself to judge instability, and the beginners at whom this article is clearly targeted need to know this more than the experts.

Also from page 1 of the series:

A common crystal type that is particularly dangerous due to its inability to bond with other snow crystals is know as ’hoar.’ Hoar snow, also called ’sugar snow’ because of its similarity to granulated sugar, can be found at any depth or at multiple depths in a deep snowpack.

"Hoar" isn't really the correct term. The author should refer to facets, surface hoar, and depth hoar, or refrain from using any terminology except for "sugar snow" or perhaps "coarse snow". The other problem is that very fine layers of facets ( such as facets above or below a crust ) can be very easy to miss. The difficulty in identifying thin weak layers should be noted in the article.

Also from page 1 of the series:

Snowstorms pile up one after the other all winter long. Wind blows snow off of some slopes and on to others. Temperature changes cause snow crystals to metamorphose. If the snow’s consistency remains constant, the snowpack is homogenous and stable. It’s when the snowpack develops different layers of different snow types that it becomes unstable and hazardous.

This paragraph started out so well... Unfortunately, the statement about constant consistency being an absolute measure of "stability" is entirely wrong and dangerously misleading. First, snowpack evaluation is framed around the search for instability, and second, a beginner should not judge the stability of the snowpack by consistency alone because it is very easy to miss important signs of inconsistency. Better to err on the side of caution if you just don't know.

From the second page in the series:
  1. Dig a pit 5 feet deep or to the ground (whichever comes first) on an open slope after probing to see if there is any old avalanche debris, rocks or brush in the way. Make the face of the pit smooth with your shovel.
  2. Use a glove to brush the surface of this wall to see if there are visible layers.
  3. Use a credit card or driver’s license and, holding it lightly, slide it down the wall. Notice where the card catches on hard layers.
  4. Do the same starting at the bottom and sliding up.
  5. Next, do a finger test for soft layers, running your gloved hand first down and then up the wall. Note where the hard layers (possibly sun or wind crust) and the soft layers (depth hoar) are located.
  6. If you don’t detect any significant layers in the snow, you can continue on your trip. But if there are crusty or soft layers, you should then perform at least one of the following tests.
This isn't really the correct procedure for performing a snow profile, although it clearly tries to communicate the right information. Use a driver's license or credit card? It would be better to provide an explanation of how to excavate the profile and use simple tests to evaluate layering and determine if hardness increases with depth. There is a very strong relationship between data sampling and perception of instability, and the rudimentary tests discussed here could miss important details. It's better for most recreational backcountry skiers to avoid formal profiles and focus on snowpack tests instead ( which are outlined on the page ).

Also from page 2 in the series:

The Rutschblock test is fairly reliable in predicting fracture initiation (how much force is required to start an avalanche). The Extended Column Test has become more popular because it not only predicts fracture initiation, it includes fracture propagation (how big the avalanche might be). The ECT is also easier to perform since the size of the isolated block is smaller.

Shear quality analysis derived from rustchblock tests can also provide valuable information about fracture propogation. It is worth mentioning that the ECT most certainly DOES NOT predict avalanche size, and even if it did, most people are killed by small avalanches that don't travel very far.

Also from the page 2 in the series:

If you have to jump in the middle of the block, there’s likely a low chance of avalanches on slopes with similar angle and aspect.

This is only true if you ignore spatial variability.

Also from the page 2 in the series:

A Q1 shear is of more concern to the backcountry traveler than a Q3 shear.

First, this is non-information, and second, after spending most of the page discussing how to perform snowpack tests, the author neglects to discuss the importance of shear quality. Not only that, but Q1 and Q2 shears have roughly the same importance with respect to skier-triggered avalanches. Here's the skinny on shear quality for beginners: if you observe shears that are rapid, sudden, or smooth, then you have uncovered a clear sign of snowpack instability.

Anyway, I want to be clear that this is not an attempt to criticise REI, but at the same time, it would be very easy for REI to check this information with a local guide service.

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