A winter trip into Yellowstone’s backcountry can be the adventure of a life time. Whether you plan on entering this spectacular wilderness for a day or on an extended trip, you should be aware of the potential for avalanches.
In reality, all that is required for an avalanche to occur is a mass of snow and a slope to slide down. But, several factors can combine to raise the avalanche danger. The first factor to look at is the weather.
Most avalanches occur within a day or two after a heavy snowfall. This means you need to know what the conditions were like on the days preceding your trip. You can learn a lot by talking to a ranger at a visitor center or a backcountry office.
Surface Hoar is formed on calm and clear nights. These beautiful ice crystals form a weak layer once they are covered by snow. Depth Hoar develops within the snowpack and can be very dangerous. It forms when there is a large temperature gradient within the snowpack.
Wind can also be a big factor to consider. As wind rises up the windward side of a mountain it erodes the snow and carries it up and over the ridge. The snow is then loaded onto the leeward side of the mountain. The added weight raises the avalanche danger drastically.
Slope angle and slope orientation are also important. Most avalanches occur on slopes of 30 degrees or more, but wet snow can slide on slopes as low as 10 degrees. Here in the United States, the majority of slides are on the north, east and northeast side of mountain ranges.
Be aware of the terrain you are crossing. Avoid gullies and bowls if possible. The snow can build rapidly in those types of areas. Small depressions located between steeper slopes can be dangerous. These places are called terrain traps for a reason.
Conditions can change rapidly in Yellowstone. Take the time to research avalanches before you begin your adventure. You can find some great information by visiting our website. (http://www.nps.gov/yell/avalanche_information.htm) By understanding the dynamics of avalanches, you can develop the skills needed to survive in this winter wonderland.