The Outsider: Ten commonly used avalanche terms

Like most backcountry travellers, I don’t study enough snow science.

I read bulletins the night before (and sometimes morning before) I head out into the backcountry, practice with my self-rescue equipment in the early winter and try to ask a lot of questions when I’m out with people who have more training and experience than I do.

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But the language of avalanches can sometimes get a little technical. The good news is that Avalanche Canada has made sweeping changes to its forecasts in recent years to simplify the language and break up paragraphs of texts with infographics and more digestible data. But there’s always going to be a few terms that may slip by your avalanche vocabulary.

To that end, here are 10 commonly used avalanche terms that should come in handy the next time you read the bulletin, or if you want to impress your buddies with your avalanche know-how.

Ablation. The opposite of accumulation. Commonly used in the context of “ablation zone,” in reference to an area of a glacier that that is receding.

Aspect. The direction that a slope faces. For example, north aspect slopes face toward the north. Important when considering the effects of solar radiation or wind loading on the snowpack.

Bed surface. The surface across which a slab avalanche releases. This can be the ground, but is usually a crust or a harder layer of snow. Not to be confused with a weak layer.

Cross-Loaded. When wind blows across a cross-loaded slope, snow is picked up from the windward side of ribs and outcrops and is deposited in lee pockets (see below), which can release if triggered by a skier, snowboarder or snowmobile.

Depth Hoar. Large, hollow snow crystals with edges, rims and ripples on the surface, the result of faceting (see below) amidst high internal temperature disparities in the snow pack. Depth hoar is an accumulation of cup-shaped crystals and often generates weak layers in the snowpack.

Faceting. When snowflakes morph into angular grains that bond relatively poorly to one another and can create a weak layer. Rate of faceting depends on the temperature gradient (i.e. the difference in temperature throughout the snowpack).

Lee slopes. Areas on the down-wind side of ridges and other terrain obstacles, where wind flow often deposits deep accumulations of snow. Usually refers to those slopes sheltered or protected from the wind. For example, an east-facing slope is in the lee of a west wind.

Sluffing. Progressive stabilization of steep snow slopes by small, usually harmless avalanches. Technically, a sluff is any snow slide that moves less than 150 ft (50 m) slope distance.

Surface Hoar. "Crystals, often shaped like feathers, spikes or wedges, that grow upward from the snow surface when air just above the snow surface is cooled to the dew point. The winter equivalent of dew. Surface hoar grows most often when the wind is calm or light on cold, relatively clear nights. These crystals can also grow during the day on shady slopes. Once buried, layers of surface hoar are slow to gain strength, sometimes persisting for a month or more as potential failure planes for slab," according to Avalanche Canada.

Tension zone. A snow slab is placed in tension by the straining and stretching of the snowpack over terrain irregularities. The tension zone of a slab occurs at the top where the slab is trying to pull away from the stable snow.

Don’t forget that these terms are only useful in the broader context. That means getting trained by a professional on an avalanche course, observing avalanche bulletins and learning from a mentor.

Vince Shuley is constantly working on his avalanche vocabulary. For questions, comments or suggestions to The Outsider email vince@vinceshuley.com or Twitter @vinceshuley.

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