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As Richard looked up, he saw a wall of snow …and suddenly couldn't hear anything except the deafening sound around him as the avalanche carried him down at 100 mph through trees and boulders. 
In the past four years, there have been 23-36 deaths per year in the U.S. from avalanches. Avalanches are the only natural hazard commonly triggered by the victim and cause more deaths than any other natural hazard. 75% die of asphyxiation and 25% secondary to trauma with only 2% succumbing to hypothermia. Victims usually don't live long enough to become hypothermic. There is a 93% survival rate if found within 5 minutes. 50% of all completely buried victims die within 25 minutes. 95% are dead in 2 hours. Avalanche debris is 60-70% air. Victims die from CO2 toxicity as it builds up in the snow around their mouth and has nowhere to vent.
Loud noises do not trigger avalanches. A slough is loose snow sliding down a mountain to be distinguished from a slab breaking off. Slabs account for almost all serious avalanche injuries and fatalities. The most common type is a dry slab avalanche, where a plate of dry snow cracks off as it is suddenly overloaded by a person stepping on it. It cracks off as one big piece, then shatters as it slides, like a plate glass sliding off a table. These avalanches reach speeds of 60-80 mph within 5 seconds. When they stop, the snow and ice set up with the consistency of concrete because the tumbling action generates friction and secondary heat during the slide, which quickly dissipates as the slide stops. In Utah alone there are 100,000 avalanches/yr. with over 100 triggered by humans. 99.9% occur in the backcountry. Almost all involved are highly skilled in their sport. Two times as many are snowmobilers as they cover 100 times the terrain per day as a skier can. Others in order of incidence are skiers, climbers, snowboarders, snowshoer, hikers and hunters.
Avalanches are not accidental, but predictable depending on the environmental factors of terrain, snow pack and weather.
Terrain: Most occur at slope angles between 35 and 45 degrees. If the slope is less than 25 degrees then it is usually not steep enough to sustain a slide and if it is steeper the snow tends to slough rather than accumulate. Watch out for barren open slopes usually from trees being wiped out by rock slides and avalanches. Wind loaded steep slopes are very dangerous. North facing slopes have increased risk in the winter because the snow does not have an opportunity to warm up and bind its individual layers together. South facing in the spring are higher risk due to rapid warming that can cause instability between the layers as melting occurs. For traveling ridges are safer, staying away from the cornices and remembering that the ridge may be 10 to 20 feet back from the visible edge of the cornice. A lower slope angle is safer as long as you stay well away from surrounding steeper slopes. Remember that the first step up a steep slope can send the entire slope down on you because the plate is connected as one gigantic slab. Pressure on any part of the plate can cause it to release, not just the top. Dense trees are like anchors anchoring the slab in place at multiple points making it much safer for travel.
Snow pack: When it is unstable enough it only takes a little more load (the weight of a person) to cause it to slide. One danger sign is natural avalanche activity. This is obvious but often overlooked. Wind slabs are extremely dangerous. The worst condition is when there is a dense layer of snow over a light, loose layer of snow. The National Avalanche Center coined the term “brick over potato chips” If you hear collapsing snow with a whoomph sound or see the snow start to crack in places prepare to get out fast.
Weather: Changing weather increases the avalanche risk. Rapid precipitation makes the snow pack more unstable as it has no time to adjust to the new load. Wind redistributes snow, even with blues skies and can deposit new snow ten times faster than snow falling from storms. Also the snow that is deposited is denser as we say “wind-blown.” When wind blown snow is deposited over fresh light snow, watch out! The other factor to consider is temperature. Warmer temperatures make snow packs more stable because it allows the layers to gradually settle and bond together unless there is rapid warming which then reduces stability because the layers can slide past each other due to melting.
Combine the correct risk factors of terrain, snow pack and weather with a trigger, the weight of the victim, and it suddenly overloads the slab causing it to fracture and then you have an avalanche.
Preparing for a backcountry outing: Call the Forest Service National Avalanche Center for an updated report or check on the internet at www.avalanche.org . The phone numbers are listed there under “avalanche centers.” Avoid avalanche terrain or recognize it and know how to assess danger. Practice with your beacons and make sure the batteries are fresh. Test slopes at a 45 degree angle with a good escape route. Use snow pits to check for instability layers. Descend one at a time. Move from island of safety to island of safety (for me typically lots of huge pine trees close together) Look for your way out in case. Open bowls that are funnel shaped (most of them) are a lot of fun, but can be death traps as well with no easy way out. Areas with multiple ridges and/or thick trees are better. Travel at least in pairs and move a safe distance away from the slope just skied.
Backcountry minimum avalanche list: beacon, shovel, probe. Don't ever put the beacon in your backpack.
Backcountry survival list: Most people who are stranded do not plan on it, so it is better to be over prepared than under, besides your legs get a better workout from carrying all that extra weight. The list can include snowshoes, slope meter, camp saw, waterproof map, compass, whistle, signal mirror, first aid kit, cell phone, metal matches, match safe with matches, a fire-starter of your choice, metal container for melting snow, small hunting knife, leatherman or equivalent, duct tape, headlamp with extra batteries, hand warmers (lots) , extra clothing, space blanket, high calorie food, sunscreen, etc. Make sure you know how to make several types of snow shelters as well.
When all else fails: You are in the avalanche wondering whether you will survive. What to do? Keep head up, lose skis, board, snowshoes or anything else that could serve as an anchor pulling you down, swim, grab objects, ski or board out to one of your preplanned escape routes, especially good when done at the beginning, as the snow stops, place hands in front of face to clear an air space and thrust a hand upward (hopefully you know which way is up) and pray. There are devices on the market worth considering for the avid backcountry person including devices that draw air from the surrounding snow such as the Avalung II which can increase your survival time.
Good news: Over the past four years there have been no reported fatalities or close calls in the state of Arizona . At least none reported to the National Avalanche Center . So it seems Arizona is safer which is probably attributed to the generally warmer temperatures which stabilize the snow pack. If you are going to any of the other Rocky Mountain States or even a few others, then pay heed to this article. You will be on unfamiliar territory with much higher avalanche risks. For a chart of avalanche fatalities by state and sport click here or go to www.avalanche.org for more information as well.
Mark D. Hopkins, M.D.
Board-Certified Orthopedic Surgeon
Avid outdoor enthusiast
 From Hospital Privileges, page 56, a novel based on a true story