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Avalanches
by Tara Horvat
Physical Geology
Spring 2015
  
 
 

How to Avoid an Avalanche
 

            Avalanches are an intriguing force of nature. People often overlook just how powerful and deadly avalanches can be. According to the National Snow and Ice Data Center, an avalanche is a rapid flow of snow down a hill or mountainside. Avalanches can occur at any time of the year, however, they occur most frequently during the months of December through April.
 


 

            If you have ever lived in an area where it snows during the winter months, then it is likely that you have seen “mini avalanches.” Show will build up on the windshield of a car. Then as the temperature starts to rise, the snow on the windshield will slide off. This is a good representation of what takes place on a mountain or hill, only on a much larger and deadlier scale.
 

            Avalanches kill roughly 150 people every year. About ninety percent of avalanches are caused by humans. The people who are most affected are snowmobilers, skiers, and snowboarders. In order to avoid an avalanche, or even survive one if it comes to it, one must first understand as much as they can about them.

            Most avalanches are fairly small and consist of a dry powder snow and moves in a formless mass. These small avalanches only cause a fraction of the death and destruction in comparison to avalanches on a much larger scale. Large scale avalanches take place when a large mass of snow breaks loose from a mountainside. These disastrous avalanches can reach eighty miles per hour within about five seconds. Speeds like this make it extremely hard to escape an avalanche.
 

            There are several factors that have an effect on the cause of avalanches as well as how the avalanche acts while in motion. Avalanches are most likely to occur during within 24 hours after a winter storm that brings 12 or more inches of new snow. The fresh snow becomes too heavy for the original snowpack which causes a weak layer underneath to break. The layers of a snow pack vary depending on recent winter weather patterns. Various conditions that affect how the layers bond include rain, hard freeze, heavy snow, and drought. The bond of the layers is important because it affects how easily a layer may or may not break and cause a slide.


            Avalanches also have their own anatomy. They are separated into three parts. These three parts are the starting zone, avalanche track, and runout zone.


            The starting zone, as its name represents, is where unstable areas of the snow pack fracture and begin to slide off the mountain. These areas are very volatile and are generally located higher up on slopes. However, if conditions allow, the avalanche can begin at any point on the slope.


            The avalanche track is the path the snow takes when sliding down the slope. The avalanche track will often have signs if the area frequently has avalanches. Some of these signs include large areas of trees missing from a slop, chute-like clearings, and large pile-ups of debris and snow at the bottom of the slope.
 

            The runout zone is where debris and snow end up. This is also called the deposition zone where debris and snow will pile up the highest.
 

            There are some other key points that are important to consider about avalanches. The first consideration is the steepness of the slope. Slopes with a steepness between 30 and 45 degrees have the greatest risk of avalanches. Slopes with a steepness between 25 and 60 degrees are less likely to have avalanches, but it is still possible given the right conditions.
 


 

            The second consideration is the profile of the slope. Slopes that are convex are the most dangerous, while concave slopes present less of a threat. Again, with the right conditions, concave slopes can still avalanche.


            The next factor to consider is the aspect of the slope. Slopes that face the north are the most dangerous during the middle of winter. Slopes that face the south are more likely to avalanche during the spring or on sunny days once the sun begins to rise higher in the sky.
 

            Yet another consideration is ground cover. Smooth, grassy slopes are more likely to avalanche than areas with plenty of trees, heavy brush, and large rocks. These terrain features help to anchor the snow in place.
 

            The final factors to consider involve weather and the snow itself. Wind that blows consistently at 15 miles per hour or more during a storm increases the threat of an avalanche. Also, according to avalanche.org, “snow plumes from ridges and peaks indicate that snow is being moved onto leeward slopes during clear weather and that dangerous conditions may be developing, even though it is not storming.” Temperature also plays a factor in the threat of an avalanche. When the temperature is cold, snow will remain in an unstable state. The snow will settle and stabilize under warmer conditions, more specifically near freezing or just above. However, when the temperature rises in the spring it creates the risk of wet snow slides. Rapid rises or falls in temperature also create dangerous conditions. A rate of snowfall more than one inch per hour will also increase the danger of an avalanche.


            New snow fall will create an elevated risk factor. This is usually the case when more than 12 inches of snow falls, however less snow can also be just as dangerous. If old snow was already covering natural anchors such as brush and larger rocks, then new snow that falls will be at a greater risk to slide. This also applies to lose or dry snow.
 


 

            The shape of the snow is also an indicator of whether an avalanche is a greater threat. Snow with a needle or pellet-like shape is more dangerous than snow with star shaped crystals. This can be observed by letting the flakes fall onto a dark ski mitt or a parka sleeve. Snow that sounds hollow indicates dangerous conditions as well. Listen and watch for cracks in the snow. This means avalanche danger is very high.
 

            Now that the basics of avalanches have been introduced, the question of how to avoid an avalanche can be answered.

            As mentioned beforehand, it is important to let the snow settle. It is best to wait 48 hours after a snow storm before going and enjoying the fresh powder. Just remember, various conditions can lengthen the amount of time necessary for the snow to settle. You can go to avalanche.org to find an avalanche forecast for your area.
 

            Be sure to assess the slope of the mountain you are on. Take an inclinometer to accurately assess the angle of the slope. Remember, slopes between 30 and 45 degrees are the most prone to avalanches. If possible, find another route to avoid the steeper slopes.
 

            If you absolutely have to cross a steep slope, cross at the highest point possible. If an avalanche occurs, you will be more likely to survive if you are more towards the top of it.


            Watch for trees and other natural anchors. Avoid areas that are lacking in these anchors. This is an indicator that avalanches occur in the area. Also look for broken branches on the uphill side of the trees. This is also a good indication that avalanches occur in the area.
 

            If you come across an area where there is possible danger, be sure the members in your group cross the area one at a time. Keep your group sizes between 3 and 5 people. If there are only two members in the group and one gets caught in an avalanche, the other will have to choose between going to get help and trying to rescue the person. Groups with more than 5 people can become fragmented which will increase the safety risk.
 


 

            Avoiding an avalanche is imperative to safety. If caught in an avalanche it is very difficult to survive. 93 percent of avalanche victims survive if dug out within 15 minutes. After that, survival rates drop significantly. After 45 minutes only 20 to 30 percent of victims survive. Very few people make it after two hours.

            If you do get caught in an avalanche, try to get off the slab. This will be very hard to do. If you cannot get off the slab, then reach for a tree. Otherwise make swimming motions upward to keep from sinking downward. Also keep your mouth closed so it is not filled with snow. When the slide begins to slow try to clear air space and then punch a head upward. Once the slide stops the snow will become like concrete and you will not be able to move.
 

            If you are with someone who gets caught in an avalanche, mark the spot where you last saw the victim. If there is another member in your group, then send that person to go get help. Otherwise you should not leave the victim. Their best chance to survive is if you get to them within 15 minutes. Search for the victim in the fall line and directly below the last seen point. Be sure to search the area of greatest deposition first. Recall that this is the point where snow and debris has piled up the highest.


 

 

References

Photos by Ilan Adler (www.Putchka.com)

http://www.backpacker.com/skills/beginner/winter-camping/how-to-avoid-avalanches/

https://nsidc.org/cryosphere/snow/science/avalanches.html

http://environment.nationalgeographic.com/environment/natural-disasters/avalanche-profile/

http://www.avalanche.org/moonstone/rescue/GENERAL%20RULES%20FOR%20AVOIDING%20AND%20SURVIVING%20SNOW%20AVALANCHES.htm

http://www.telegraph.co.uk/travel/snowandski/6980399/Ski-safety-how-to-avoid-avalanches.html