What makes avalanches dangerous

Always stay within view of your group. Avalanches may reach the road without warning. Obey road closures. When the avalanche hazard is high, control work by explosives may be carried out at any time. If an avalanche blocks the highway, remain in your vehicle with seat belts on. Wait for assistance. It is easier to find a car in the snow than it is to find a person. Drive to a safe area if possible. That's a great question, Wonder Friend Isaac! We're happy you're thinking about avalanches and how they are formed!

Scientists may have different answers about the biggest avalanche ever, but there have been quite a few big ones in history! Sometimes it's measured on the amount of snow, sometimes it depends on the length of time, and sometimes it is determined by the number of people involved.

Hey there, Wonder Friend George! Thanks for sharing your awesome tip! We think it's cool that gravity can help someone when an avalanche occurs. We're so proud of you! Thanks for visiting us! If avalanches could talk, we bet that's exactly what we'd hear!

Nice work, Tyler J! We hope you never encounter an avalanche in your lifetime! Hi there, Wonder Friend Achia! While you cannot always prevent avalanches from happening, it's important to pay attention to the warning signs of an avalanche. Take a look at the excerpt below for more information: "Avalanches usually occur during the winter and spring, when snowfall is greatest.

In addition to being dangerous to any living beings in their path, avalanches have destroyed forests, roads, railroads and even entire towns. Although avalanches occur suddenly, warning signs exist that allow experts to predict — and often prevent — them from occurring.

We're so glad you learned something new, Janhavi! Avalanches can be scary, but that's why it's important to be prepared and aware of your surroundings. And always travel with a buddy! Thanks for sharing your comment, Wonder Friend! WOHOO, we're so excited that you had fun creating an avalanche of your own! Great work, Chloe! It's important to be safe, especially when a storm is brewing!

Thanks for pointing that out, Autumn! Have a super day! WOW, we bet you like to stay nice and warm, Danny! Snow can be fun, but sometimes it makes you want to enjoy the warmth of the indoors!

We can't wait to find out what tomorrow's Wonder will be! We're glad you learned something new today, Josephine! We are happy to know that you visited Wonderopolis today-- we love learning with new friends! WOW, what an interesting fact to add to today's Wonder, Mark! Thanks for sharing that information with us, Wonder Friend! We're so very sorry to hear about your father, Megan. We are thinking of you-- thanks for reminding us to be safe, too!

WOW, thanks for sharing your ideas for tomorrow's Wonder, Cailyn! We hope you're having a great day in Minnesota! Thanks for telling us how you feel about the snow, Bryleigh! We bet it can get very cold in Colorado, especially in the winter! We're glad you're visiting us today at Wonderopolis though!

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By the way, when you get stuck in an avalanche, how do you know where the surface is? Jan 9, Juana Dec 6, If you're under snow and don't know if you're right side up or not you spit and were the spit falls you dig in the opposite direction. Dec 11, HI, Juana!

Thanks for the advice! Hey me Oct 27, Arizona's single avalanche death was an out-of-bounds snowboarder killed in For more information, see the statistics compiled by the Colorado Avalanche Information Center. While expertise is not a guarantee that you won't be caught in an avalanche, it does provide some basic knowledge about how to avoid avalanche areas, what types of weather and terrain signs to watch for, and what to do if you are caught in an avalanche - all information that may save you or other members of your party.

The three parts of an avalanche path: starting zone, track, and runout zone. Photograph courtesy of Betsy Armstrong. All that is necessary for an avalanche is a mass of snow and a slope for it to slide down. For example, have you ever noticed the snowpack on a car windshield after a snowfall? While the temperature is cold, the snow sticks to the surface and doesn't slide off. After temperatures warm up a little, however, the snow will "sluff," or slide, down the front of the windshield, often in small slabs.

This is an avalanche on a miniature scale. Of course, mountain avalanches are much larger and the conditions that cause them are more complex. A large avalanche in North America might release , cubic yards of snow.

That's the equivalent of 20 football fields filled 10 feet deep with snow. However, such large avalanches are often naturally released. Skiers and recreationists are usually caught in smaller, but often more deadly avalanches.

Slab avalanches are the most common and most deadly avalanches, where layers of a snowpack fail and slide down the slope. Since , people in the U. Hard slab avalanches involve large blocks of snow and debris sliding down a slope. In soft slab avalanches, the snow breaks up in smaller blocks as it falls. An avalanche has three main parts. The starting zone is the most volatile area of a slope, where unstable snow can fracture from the surrounding snowcover and begin to slide.

Typical starting zones are higher up on slopes, including the areas beneath cornices and "bowls" on mountainsides.

However, given the right conditions, snow can fracture at any point on the slope. The avalanche track is the path or channel that an avalanche follows as it goes downhill. When crossing terrain, be aware of any slopes that look like avalanche "chutes. There may also be a large pile-up of snow and debris at the bottom of the slope, indicating that avalanches have run. The runout zone is where the snow and debris finally come to a stop.

Similarly, this is also the location of the deposition zone, where the snow and debris pile the highest. Although underlying terrain variations, such as gullies or small boulders, can create conditions that will bury a person further up the slope during an avalanche, the deposition zone is where a victim will most likely be buried. Several factors may affect the likelihood of an avalanche, including weather, temperature, slope steepness, slope orientation whether the slope is facing north or south , wind direction, terrain, vegetation, and general snowpack conditions.

Different combinations of these factors can create low, moderate or extreme avalanche conditions. Keep in mind that some of these conditions, such as temperature and snowpack, can change on a daily or even hourly basis.

This necessitates constant vigilance of your immediate surroundings while doing any wintertime backcountry travel. The route you chose may be safe when you begin, but may become dangerous if conditions change dramatically throughout the day. While this may seem like a lot of work, once you understand factors that can cause avalanches, most of these signals require simple observation to evaluate your surroundings as they change.

Simply ask yourself, when are conditions sufficient to cause a mass of snow to slide down a slope? The following factors often occur in combination to produce an avalanche, but if a slope is unstable in any way, it may take only the weight of one skier to set off an avalanche. The more foresight you have about conditions and situations to avoid the safer your outing will be.

Avalanches are most likely to run either during or immediately after a storm where there has been significant snowfall. The 24 hours following a heavy snowstorm are the most critical. Consequently, it becomes important to be aware of current weather conditions as well as the conditions from the previous couple of days. Temperature, wind, and snowfall amount during storms can create fatal avalanche conditions during your outing. If there has been heavy snowfall the day or night before your trip, it may be wise to postpone the trip in order to avoid the increased avalanche danger.

Recent snowfall puts extra stress on the existing snowpack, especially if it does not adequately bond to the pre-existing surface layer. The extra weight of new snow alone can cause a slab to break off and fall down the slope, particularly in storm-induced avalanches. Snowfall amounts of one foot or more frequent in mountainous areas create the most hazardous situations, producing avalanches that are often large enough to block highways and cause major destruction.

Amounts of six to twelve inches pose some threat, particularly to skiers and recreationists. Amounts less than six inches seldom produce avalanches. Because snow is a good insulator, small temperature changes do not have as much effect on snowpack as larger or longer changes do. For instance, shadows from the sun crossing the snow surface throughout the day will not significantly change snowpack stability.

Changes that last several hours or days, such as a warm front moving through, can gradually increase temperatures that cause melting within the snowpack. This can seriously weaken some of the upper layers of snow, creating increased avalanche potential, particularly in combination with other factors. When temperatures rise above freezing during the daytime and drop back down again at night, melting and re-freezing occurs, which can stabilize the snowpack.

This is particularly common during the springtime. When temperatures stay below freezing, especially below zero degrees Fahrenheit, the snowpack may remain relatively unstable. Wind scouring snow off of the windward side of the peak and depositing it on the leeward side. Photograph courtesy of Richard Armstrong. Wind usually blows up one side of a slope or mountain the windward side , and down the other the leeward side.

Blowing up the windward slope, wind will "scour" snow off the surface, carry it over the summit, and deposit it on the leeward side. What this does is pack snow unevenly on the leeward side, making it more prone to avalanche. A cornice or icy overhang at the top of a mountain or ridge is a telltale sign of wind scouring. It is safer to travel on the back, or windward side of such a slope, where the snow layer is thinner and wind-packed.

Although it seems like a small amount because the snow may look light and powdery, the weight can add up significantly and can be a critical factor if a slope is already unstable.

In the Northern Hemisphere, storms generally move from west to east. Consequently, the leeward slopes are most often the northeast, east, and southeast facing slopes. These slopes become easily wind-loaded and will more readily avalanche. Many ski areas are built on slopes with these orientations and must use prevention measures to counteract the natural avalanche conditions that build up on these slopes.

Perhaps the most significant factor but not the only one is how the snowpack has developed over the season. We only see the surface and maybe the top few layers of snow, but it can be layers of snow several feet deep that may ultimately determine whether the slope will fail. A new layer of surface hoar on the snow. Note the quarter for scale. Photograph courtesy of K.

Understanding the history of snowpack for that season can reveal several clues about slope stability. The snowpack as a whole may change not only during the course of the winter season, but throughout the course of a single day, due to changing weather and temperature conditions. This is why constant awareness and frequent slope testing are necessary.

Snowpack conditions are extremely important because many layers of snow build up over the winter season. Each layer is built up under different weather conditions and will bond differently to the subsequent layers. This metamorphism allows them to compress and generally form stronger bonds. In between snows, the temperature may rise and melt the exposed surface layers, which when they re-freeze create a smoother, less stable surface for the next snowfall.

Failure is much more likely to occur during or after the next few snowfalls. Rain between snows creates a slicker surface as well, and can weaken the bonds between snow layers. On the other hand, light snowfalls and consistently cold temperatures help strengthen the snowpack and make it more resistant to avalanche. Weak layers deep in the snowpack can cause avalanches even if the surface layers are strong or well bonded. A type of snow called depth hoar a course, grainy form of snow crystal is often the culprit behind avalanches.

Because of its granular structure, similar to dry sand, depth hoar bonds poorly and creates a very weak layer in the snowpack. Unfortunately, the weather conditions necessary to produce depth hoar most often occur very early in the season, and these weak layers are buried under subsequent snows.

All too often, deeper depth hoar layers are discovered only after an avalanche has swept off the overlying layers. Most avalanches occur on slopes between 30 and 45 degrees, but can occur on any slope angles given the right conditions. Very wet snow will be well lubricated with water, meaning it might avalanche on a slope of only 10 to 25 degrees.