Physics of Avalanches :: physics snow avalanche

Avalanches are just one of many natural disasters that kill people every year. The difference to Alaskans is that this disaster hits a little closer to home than most. The fear of hurricane and tornado are not existent in my region, and even earthquakes are seen more as a little shake then any threat. Physics plays a huge part in avalanches, thermodynamics, statics, and gravity are just a few elements of these disasters. The map above confirms that Alaska is at high risk for avalanche. As a result of this threat, learning about avalanches is a necessity when recreating or working in high avalanche areas. In order to better understand Avalanches, it makes sense to first learn about what avalanches are compose of, snow. Snow forms when atmospheric conditions cause water vapor to condense. However, it is obvious that all snow doesn't have the same structure. The density of fresh snowfall is dependent on both the kind of snow crystal and the air temperature. In cold, calm conditions the snowfall is the lightest. While in warmer climates, where graupel and needle crystals fall, the snowfall is the densest. When looking at a cross section of snowfall it is often evident what weather conditions formed the cross section. This is due to the different densities and structures of the snow layers. The bonds between snow layers are large factor in avalanches. If there is a weak bond between layers, the top layer can easily slide off the bottom layer. When this happens it is called a slab avalanche. Other layering characteristic will create other avalanches and hazards, such as ice avalanches and cornices. Whenever traveling in avalanche country it is important to be aware of your environment. Steep gullies and wide plains are perfect paths for avalanches. Ridges and unconformities in the terrain may help to slow down an avalanches speed. The severity of an avalanche is directly related to the terrain in which it happens. One of the most important factors to consider is the slope of the mountain or hill. Most avalanches occur between 20 and 50 degrees like the diagram above shows. However, the largest avalanches occur between 30 and 45 degrees, and the areas which have the greatest frequency of avalanches are between 35 and 40 degrees.