originally published in March 05 edition of Off Piste
“We were going to dig a pit, but it was getting late, we were cold, and the skiing looked so sweet!” Sound familiar? If so, you are not alone. Some of us are snow scientists, but most of us are just skiers. When the skiing is good, or time is running short, it’s usually the snow stability evaluation that gets the axe. Another option is to incorporate a few of the following on the fly tests into your tour and you will find yourself a lot more equipped to make good decisions when it’s time to ski down.
While there are a number of quick and dirty tests that can be incorporated into your tour, they all require setting a good uptrack. By setting a low angle uptrack that winds around through the terrain, you will feel changes in the snow from one aspect to another, sun to shade, and on different slope inclines. Many of these subtleties are missed when simply switchbacking straight up the fall line. As you set your track, try to notice how the snow feels under your skis, how it varies in texture and depth from one aspect to another. If you are following a set track, step out on occasion and see what the snow feels like to you.
The first unscientific test that I use constantly is the pole test. This test is as simple as pushing your pole down into the snow feeling for changes in snow density. A red flag here is when you feel increasing resistance against your pole basket followed by a rapid reduction of resistance. This indicates that there is weak layer underlying a stronger layer which is an inherently unstable layering structure to the snow. The beauty of the pole test is that you can do it almost constantly throughout the tour and therefore take in information about the snowpack layering on all aspects and elevations that you travel through during the day. This test can also be done with the grip end of the pole, though in either case, is not very effective at finding thin weak layers.
One of the best tools you can incorporate into your tour is trying to route your uptrack near indicator slopes. A good indicator slope shares many of the characteristics of the slopes you are planning to ski, yet with minimal consequence in the event of an avalanche. Look for small, steep, convex slopes to ski across on your way up. Jumping on a convexity can often expose a weak layer in the snow with cracks propagating, sluffing or even a small slab breaking off. Having someone ski across the bottom of the small slope will remove some of the support the slope has from below. This mimics the isolated column of snow in some of the standard bonding tests. While not as scientific or standardized, it has the advantage of being quick, easy and fun, and therefore you may actually do it. By setting an uptrack that weaves through the terrain you will have ample opportunities to look for slopes to do this on. With some experience you will begin to find many of these test slopes and can perform these quick tests several times on your tour up.
Occasionally on the course of a tour you may find yourself heading out onto a slope without feeling like you have much information about the snowpack on that slope. A quick test to employ in this case is the hand shear test. Turn your pole upside down, and with the grip slide, plunge it into the snow and cut out a block about the size of your shovel blade. It should be in undisturbed snow and deeper than any suspect layers. The downhill side of this column should already be cut out from breaking trail with your skis, though in some cases you might have to clean it up a bit. Now reach around to the back of your column and insert both hands in much like you would insert a shovel for the shovel shear test. With steady gentle pressure pull forward and look for shears in the snow. The big red flags here are clean and/or easy shears. These indicate poor bonding between layers in the snowpack.
One of the most fun slope tests is the backcountry bomb, otherwise known as a cornice. While cornices should always be treated with a healthy respect and approached cautiously, they can provide an invaluable forecasting tool. The trick is to find a safe way to drop a section of cornice onto the slope below to observe its effect on the slope. The most common method is to position a spotter along the ridge that can coach the skier just far enough out on the cornice without risk of life and limb. The tester will then anchor the downhill ski and push with the uphill ski on the cornice, always starting further back than one might initially think. The spotter can tell the tester how much farther to move out until the cornice breaks loose. If this seems too dangerous, or the cornice is simply too big to safely utilize this method, a rope or rutchblock cord can work well to saw through the cornice a safe distance away from the edge. While not a foolproof method of slope testing, dropping a 300 lb chunk of snow onto your intended line is certainly going to increase your confidence in skiing it if it doesn’t slide. If it does slide, well, that’s good information too.
Backcountry snow stability forecasting doesn’t have to mean standing around for 45 minutes in a snowpit. It should start when you begin your tour and continue until the end of the day. By taking in lots of quick information about the snowpack as you tour, you are less likely to get surprised by that weak layer that only exists at a narrow elevation band or on a certain aspect. While not meant to replace more formalized bonding tests, these on the fly tests will allow you to further tune into what’s going on under your feet and even help you decide when you might want to pull out the shovel and have a closer look.
