In this part of our dispatch from the International Snow Science Workshop in Telluride I want to to pass on some of the more practical topics that were covered at the conference. The two that I thought would be the most useful out there in the mountains were a new stability test and a strategy for digging out avalanche victims faster and more carefully. So I’ve summarized their main points for your reading pleasure:

Extended column test:

Description

When digging snow-pits, one of the key tests in our tool box for gauging a slope’s stability (read: deciding weather or not to ski it is the compression test. The standard compression test is highly effective at identifying a weak layer’s propensity to fail. However it gives no indication on how well or even if this failure will propagate throughout the snow pack.

Recent research has shown that weak layers routinely collapse under the forces generated by a skier or snowboard riding above, however these failures are often localized and do not result in a slab avalanching. For a slab avalanche to occur the failure needs to widespread. Thus the the knowledge of how well a failure will propagate should play a major role in our decisions in the avalanche terrain as to weather or not we ski a slope.

The extended Column test is a new field test, designed by Ron Simenhois of the Copper Mountain Ski Area in Colorado and the Mount Hutt Ski Area in New Zealand and Karl Birkland of the USDA Forest Service National Avalanche Center in Montana, to identify the propagation propensity of a weak-layer’s failure characteristics and thereby help us make more informed decisions in avalanche terrain.

DISCLAIMER: The Extended column test is a new test and has seen only limited field testing to-date. Although the results of this testing have been favorable, it has not yet been sanctioned by the CAA or the AAA. Like any other field test it does not stand alone but provides some evidence which together with the results of other established field tests can be interpreted to give an indication of snow stability at a specific location. In then end, it is up to the
Backcountry traveler to determine appropriate terrain based on all the information and tools available for decision making.

How you do it:

Like all good snow stability tests the extended column involves digging around in the snow pack. The key here is to select a site that is representative of the slope you want to ski.

Once a weak layer of concern has been identified the extended column test requires a column of snow to be isolated from the surrounding snowpack to a depth greater than the depth of the weak layer of interest. So far this is pretty much the same as the standard compression test. The key difference between these two tests is the size of the column. The extended column test uses a column 30-cm deep by 90-cm long (as opposed to the 30-cm by 30-cm column used in the standard compression test).

We now proceed much in the same way as we do with the standard compression test: by placing a shovel at one end of the column and loading the snow-pack by tapping 10 from the wrist, 10 from the elbow and 10 from the shoulder. Only now we are not only looking at when and where there is a failure but also how this failure spreads across the column. To do this keep tapping even after a weak layer fails and take note of how many taps it takes for this failure to propagate across the entire block.

How you analyze your results:

A general rule of thumb in interpreting the results of this test is: that a failure propagating across the entire block immediately, or within 1-2 taps after it initially appears is characteristic of an unstable slope. Obviously a slope that fails with lighter taps from the wrist or elbow is less stable than a slope that fails with harder taps from the shoulder. In stable slopes a failure may occur but typically doesn't propagate across the column.

No field test is totally reliable, but a nice feature of this test is that it is more likely to classify a stable slope as being unstable than it is to classify an unstable slope to be stable. This is especially true in cases where a weak layer lies under a hard slab.

It also important to be aware that the extended column test does not work well to access soft upper layers of a snow pack, nor does it work well in mid-storm layers.

Even given these limitations I think that you will find the extended column test to be quite a valuable tool in accessing snow stability. However, like any field test it needs to be supplemented by additional information such recent avalanche activity, an avalanche forecast, visual clues of wind loading, and an awareness of terrain features to effectively evaluate a snow-pack's stability

If folks are interested they can find a copy of Ron and Karl's paper at

http://www.fsavalanche.org/NAC/techPages/articles/06_ISSW_Simnhois.pdf


Strategic shoveling:

Over the last decade avalanche transceiver technology has improved dramatically and a range of effective methods for their use has been the focus of recreational avalanche education. Search times have decreased so much that now the majority of time is in most avalanche companion rescues is spent digging once the victim has been located. As a result, the greatest potential for a decrease in
rescue times (and mortality rates) is in the extraction phase. Last winter Bruce Edgerly of Backcountry Access Inc developed a strategy for digging that promises not only to improve rescue times but also excavation quality.

People who have been buried in avalanches generally die of asphyxiation. Thus the key thing to remember is that the point of digging is not just to reach a victim but to provide the victim with an airway. Nearly 50% of avalanche victims are found lying face down and need to be rolled over before they can breathe. In extreme cases the act of digging haphazardly has even caused a
victim’s air pocket to be crushed by the weight of rescuers working directly above. Thus there is a real need for some care and planning to be taken in the excavation process.

Digging with no strategy creates holes in which it is nearly impossible to roll and treat a victim. Digging straight down invariably creates a cone shaped whole from which it becomes increasingly difficult to clear snow the deeper you go.

Strategy:

To prevent this problem clearly define the excavation area before you start digging.

The most effective way to dig is by terracing the downhill side of the hole, with each level getting closer to the victim.

1. Leave the probe in place. The probe should not be perpendicular to the snow’s surface but run vertically strait down to the victim. Probes with depth markings are extremely valuable in seeing how far you still have to dig and in determining the size of your starter hole.

2. Start by digging a starter whole beginning a little above the probe strike and extending 1.5 times the burial depth down the fall line. The width of this hole can be determined by the number of rescuers. If you are alone the hole can be as little as 1.25m wide to ensure adequate working space. If there are more shovelers then the hole can be extend to 2m wide to increase the probability of locating the victims head.

3. Begin digging from a kneeling position - throwing snow to the sides. Dig by chopping blocks and then removing them from the hole.

4. Start digging at the downhill side of your starter hole and work your way up to the level of the probe.

5. Once the sides of the entire starter whole are up to the shovelers waist then start digging a new terrace throwing snow downhill. This downhill end of this new whole should begin about half the way to the probe.

6. Sit on the downhill terrace and and again dig upwards towards the probe.

7. Once the victim has been reached determine the location of the head and focus on revealing the victims face. The key is to establish an airway as quickly as possible.

If there is more than one rescuer, then two should dig side by side. With more than two diggers, people inevitably will get in each others way in the hole. In these situations it is far more efficient for rescuers to rotate between shoveling and resting every couple of minutes.

This technique for digging shows promise for decreasing overall companion rescue times and improving workspace during victim recovery. However as with any avalanche rescue, the key is not needing to get rescued at all.