Snowpack - Snowmobilers

Snowpack To get an avalanche, you need a steep slope plus unstable snow. **Recent avalanches indicate unstable snow. On these days avoid steep slopes; however, when the snow is stable you can ride on anything you want. Learn how layers form in the snow. Watch the video to the right>>**
How do we know when the snow is unstable? Nature gives us lots of clues or red flags when the snowpack is unstable. If you see one avalanche, more are likely to occur. Getting stuck a lot? When loose, weak snow sits under stronger denser snow causing you to get stuck easily, this is a good sign that the snow may be unstable. This situation occurs often in early winter when many people describe this loose, weak snow as rotten.	Look for recent avalanches like ones in this photo. Similar slopes are likely unstable. Look for other clues like shooting cracks in the snow. If you hear any whumpfs in the snow, this is also a sign of unstable snow not to be ignored.
	Sometimes obvious clues are not present We don't always see clues like recent avalanches, but weather plays a significant role. Learn to recognize when weather makes the snow unstable. Next Section: Weather »

Snowpack

To get an avalanche, you need a steep slope plus unstable snow.

When the snow is stable you can ride or tour anything you want...when it is unstable...watch out!

How do we know?

Learn how layers form in the snow. Watch the video to the right>>

Look for obvious clues

The first step is to realize that a typical snowpack is actually a series of different layers stacked on top of each other. These layers are formed by precipitation, varying temperatures, and wind events that occur throughout the winter. The layers can deviate from very hard icy layers to very soft loose "sugary" layers and everything in between (check out the "Snow Pack Layering" video, top right).

The most treacherous type of unstable snowpack occurs when a slab sets on top of a weak layer. A slab is a layer of snow that has at least some cohesion. Slabs can be quite hard or they can be rather soft; the slab layer just has to be more cohesive or harder than the layer below it.

The most dangerous situation occurs when the upper layer is very cohesive and the lower layer is much less cohesive. In those situations, the upper or slab layer is literally a block that you can cut out and pick up and the lower or weak layer is like sugar.

Sometimes the weak layer can just barely hold up the block.

When that happens, it just takes a little additional stress or weight like a snowmobile to collapse the weak layer and trigger an avalanche (see video at right).

Another type of unstable and potentially dangerous snowpack occurs when above freezing temperatures melt portions of the snow pack and saturate certain layers. This condition can cause wet avalanches.

To reduce your risk in avalanche terrain you must be able to recognize unstable snow packs. Mother Nature gives us lots of clues or red flags when the snowpack is unstable and there are also tests we can do to gage stability. But before we discuss Red Flags and Stability Tests, let's take a look at how weather affects snow stability.

Next Section: Weather »

In the above diagram, the buried weak layer has collapsed and the overlying slab layer has fractured and avalanched.

When you see "snow snails" like this they indicate wet and potentially unstable snow.