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Combine steep mountains with abundant snow and you have the makings of an avalanche. An avalanche or snow slide is a mighty force of nature. Imagine tons of snow hurtling down a mountain slope! Within 5 seconds the snow reaches a speed of 80 miles per hour!

As the growing force of the snow roils downhill, trees are snapped in two like matchsticks and everything in the way is buried under layers and layers of snow. Within seconds the layers are as hard as concrete. Obviously, the best and safest way to see an avalanche is on TV!

Not all avalanches are the same. Avalanche professionals call a bunch of loose snow sliding down a mountain “sluff”. And while sluff can be deadly, it is the “dry slab” avalanches that claim more lives per year than either hurricanes or earthquakes.

In this case a slab is a huge cohesive plate of snow. It sits on other similar layers of earlier snowfall. If any underlying slab is weak or unstable it can fracture and break away under the weight of the new snow. The fracture is the starting gate for the avalanche’s downhill race. You can imagine that the deeper the weak and fracturing slab is, the greater the number of heavy layers it will take down the slope and the greater the power of its destructive rush.

On the other hand if the pre-existing snow is very stable and conditions are right, new snow can bond well with the old and the risk of avalanche is avoided.

However, nothing stays the same for long on a mountain where circumstances are as changeable as the weather. Even stable snow packs can become risky if there is strong sun, a sudden warming of temperatures or rain. Any one of these can create instability in the slabs by melting the snow unevenly.

Fortunately for skiers and snow enthusiasts there are avalanche professionals who analyze and gauge the stability of snow packs. If these experienced professionals define a section of a ski area as hazardous, the ski patrol knocks down the avalanches with explosives early in the morning before the skiers arrive.

Avalanche control is not done outside of ski area boundaries. This explains why most avalanche fatalities happen in the “backcountry” areas. Campers and skiers who choose the out of the way slopes must learn to assess avalanche risk for themselves. To help ascertain the risk, the Forest Service provides daily avalanche forecasts for various backcountry areas.

Whether you ski, snow board or just like to build snowmen, when you’re in the mountains remember to stay within the ski area boundaries or be sure to call for a Forest Service forecast. And don’t forget the hot chocolate.