1) Slab Avalanches: Most fatalities in avalanches are caused by slab avalanches. A slab avalanche occurs when a hard, cohesive layer of snow rests on top of a weaker, less cohesive layer.
Often, the weak layer can just barely support the weight of the overlying slab. The addition of even a small amount of extra weight—such as a skier—can cause the weak layer to collapse, triggering the entire slab to break free and slide down the slope. Slab avalanches typically involve large volumes of fast-moving snow. As seen in many videos showing typical slab avalanche victims (often skiers), the trigger point is usually located below the midpoint of the slab, making escape extremely difficult for the victim.
2) Loose Snow Avalanches: These are flows of low-density, powdery surface snow that typically pose lower risks. However, they can still push skiers off cliffs or into rocky terrain, causing injuries. Sometimes you may be able to ride through or stop in loose snow, but encountering it in the wrong place can be disastrous.
3) Wet Snow Avalanches: These occur during warmer temperatures when surface snow becomes saturated with meltwater. The presence of water reduces the cohesion between snow layers, leading to an avalanche.
Wet avalanches move much more slowly than dry ones but are still hazardous.
If temperatures remain above freezing for an extended period, the risk of wet avalanches increases significantly.
If your skis sink into the snow up to your ankles, the snow is likely wet enough to be avalanche-prone.
If you can squeeze a handful of snow while wearing gloves and the moisture soaks through or water squeezes out, a wet avalanche is quite possible.
So the first thing you need to determine is whether you’re in avalanche terrain—that is, whether the slope is steep enough to produce an avalanche.
The best way to assess slope steepness is by using an inclinometer or slope meter. Learning to identify avalanche terrain is the first and most crucial step in avalanche risk assessment.
Slopes under 30 degrees rarely experience avalanches. Slopes over 30 degrees, especially those exceeding 35 degrees, are highly prone to avalanches. Yet many of us enjoy skiing on slopes steeper than 30 degrees, which puts us right in avalanche terrain… If you’re already feeling thrilled, chances are you’re on a 35-degree or steeper slope.
Snowpack
Even if the slope is steep enough, an avalanche will only occur if the snowpack is unstable.
When the snowpack is stable, you can ski freely, but if it’s unstable, beware. So when you’re on a slope steeper than 30 degrees, you must evaluate whether the snowpack is stable. How do we do that?
First, understand that a typical snowpack consists of multiple distinct layers stacked atop one another. These layers form throughout the winter under varying temperatures and wind conditions during periods of snowfall.
These layers range from hard, ice-like snow to very soft “sugar” snow, as well as everything in between.
The most common unstable snowpack features a hard slab layer sitting on top of a weak layer. A slab is a cohesive layer where the snow grains bond together.
Slabs can be either fairly hard or relatively soft—the key is that the slab layer is only slightly harder and more cohesive than the layer beneath it.
The most dangerous scenario is when the upper slab layer has strong cohesion, while the lower layer lacks it. In such cases, the upper slab remains intact and can even be cut and lifted in blocks, while the lower weak layer behaves like sugar.
Often, the weak layer can just barely hold up the slab above. In this situation, even the slightest additional pressure or weight—like that of a skier—can cause the weak layer to collapse and trigger an avalanche.
Another type of unstable, hazardous snowpack occurs when temperatures rise above freezing, partially melting the snowpack and saturating certain layers with water, leading to wet avalanches.
To reduce your risk in avalanche terrain, you must be able to identify unstable snowpack. Nature provides many visual clues about snowpack stability, and there are also various tests you can perform to assess it.
But before discussing red flags or stability tests, let’s first look at how weather conditions affect snowpack stability.
Weather
Weather is the key factor in forming the snowpack and determining its stability. Understanding recent weather patterns can offer clues about snowpack stability. Similarly, listening to weather forecasts can help predict how upcoming changes might impact the snowpack.
The following weather conditions are major factors influencing whether the snowpack is stable or not:
The following climate conditions are the main factors that affect the stability of snow piles:
1) Significant short-term precipitation: Both snow and rain increase the weight of the snowpack. The greater the amount of snowfall or rainfall, the more difficult it becomes for the snowpack to handle the added weight and pressure, which increases the likelihood of an avalanche.
Rain on low-density, loose snow at low temperatures usually leads to instability and avalanches.
2) Wind: Wind-blown snow often creates dense slabs of snow on the leeward side of ridges or similar terrain. When wind transports snow from one place to another and deposits it, it adds extra weight to the existing snowpack, which often leads to increased instability.
3) Rising temperatures: Warm temperatures make the snowpack unstable in the short term but more stable in the long term. A rapid rise in temperature can cause certain layers of snow to compress and trigger movement of the entire snowpack downhill.
The compression and movement of the snowpack generally make it more unstable. Prolonged temperatures above freezing melt the surface layer of the snowpack, and the resulting large amount of water saturates the snow and weakens the cohesion between different layers, increasing the risk of an avalanche.
However, when temperatures fluctuate within a few degrees around freezing, causing cycles of melting and refreezing, the snowpack gradually becomes more stable, and fragile layers become stronger as a result.
Summary of reducing travel risks:
1. Eliminate or minimize your exposure time in avalanche terrain
2. Ensure that no more than one person is exposed to avalanche terrain at a time
On the ascent:
Always choose the safest route, which means sticking to low-angle ridges or staying within dense enough forests. If you travel through dense forests, make sure the slopes above them are not avalanche-prone open areas.
If you choose to cross avalanche terrain, ensure you move from one safe zone to another while spreading out
On the descent:
Ensure only one person is descending at a time. Travel from one safe zone to another. When you reach a safe zone, keep an eye on your partner(s)!
Reducing travel risks means you must think in terms of avalanches. When you think this way, your decisions are based on observed and tested data that reflect the likelihood of an avalanche occurring on a slope.
Never let your personal expectations override collected data and rational observations.
Thinking in Avalanche Terms:
Always be aware of changes in conditions such as terrain, elevation, or weather.
Be ready to change your plans when conditions change. Stay flexible.
Ensure everyone in your group communicates and discusses what might happen next.
Ensure that you and everyone in your group can perform quick and effective rescues. This means practicing thoroughly before you go.
Avalanche Rescue
Even when we’re careful, things can go wrong. That’s why we carry lightweight tools and know how to use them.
Typically, you should carry an avalanche beacon, a shovel, and a probe. Seriously consider wearing a helmet (nearly 30% of avalanche fatalities are due to trauma) and an avalanche airbag (which can give you up to an hour of breathing time if you're fully buried), or an ABS airbag system (the airbag helps keep the skier closer to the surface). Use bindings that release reliably… if your skis stay on during an avalanche, it's like jumping into a lake with them on—you'll be dragged down to the deepest part.
If your partner is buried, you don’t have time to call for help. You must rescue them yourself—by the time you go for help, it will be too late.
Shout for your partner or others in the area. Always keep an eye on the victim. Remember the last place they were seen.
Ensure the search is safe—don’t become another victim.
Designate a leader and quickly develop a search plan.
Look for clues on the snow surface, such as gloves, snowshoes, or other gear.
Conduct a beacon search. Approach gradually, and probe before digging.
Many of the buried victims die from asphyxiation within 15 minutes unless they are wearing an avalanche airbag.
Your companion’s chance of survival is in your hands.
It’s crucial to take an avalanche training course to learn how to perform fast and effective rescues.
Practice using beacons and performing rescues regularly before you actually face a real situation.
Rescue can be a chaotic and terrifying affair—the outcome may be grim, icy, or infuriating. But be prepared. Know what you’re doing.
If you’re the one caught
First, don’t panic. Keep your stance and try to ski out toward the edge of the avalanche flow.
At the same time, if you’re wearing an avalanche airbag, bite down on the mouthpiece immediately.
If you’re knocked off your feet and have an ABS airbag, deploy it right away.
Throw away your ski poles (never use leashes when backcountry skiing).
Hopefully your bindings are releasable and your skis have come off. If so, twist your body to face downhill. Try to swim uphill in the moving snow and make your way to the side of the avalanche.
Try to dig into a solid surface to slow yourself down and let as much snow pass by you as possible.
If possible, grab a tree.
Fight.
If the avalanche slows down, try to get a hand or another part of your body above the surface, then cover your mouth with one hand to create a small air pocket.
If you’re completely buried, stay as calm as possible and hope your companions have good rescue skills and find you quickly.
Avalanche Myths — The Mysteries of Avalanches
“Shouting can trigger an avalanche.”
In some movies, it’s a convenient plot device, but in reality, sound doesn’t trigger avalanches. It’s just a myth people tell themselves to feel less helpless in the face of death.
The power of sound is nowhere near enough to cause an avalanche, unless it’s an extremely loud explosion at close range. Even sonic booms or low-flying helicopters can only trigger an avalanche if the snowpack is already extremely unstable—and in those cases, the slope would likely have avalanched on its own anyway. In 90% of fatal avalanches, it’s the victim or someone in their party who triggers it.
“An avalanche is just a bunch of loose snow sliding down a slope.”
Avalanche professionals call that “loose snow.” Loose snow avalanches account for only a very small percentage of all avalanche injuries.
What we usually mean by an “avalanche” is a “slab avalanche,” where a cohesive layer of snow breaks like glass and slides downhill as one big block. Imagine sliding a magazine off a table—skiers are standing somewhere in the middle of that magazine.
That’s why avalanches are so deadly.“Avalanches always strike without any warning.”
We often see the word “strike” in the media. Just like stock market crashes, car accidents, or breakups might be described as “strikes,” but avalanches always have clear signs.
Besides, avalanches don’t “strike.” They happen at specific times, in specific places, for specific reasons. Again: 90% of avalanches are triggered by the victim or someone in their group.
Natural avalanches are caused by new snowfall, wind-loaded snow on weak layers, or rapid temperature rises—but there are always clear signs of instability before they occur.
“If you see an avalanche coming down from above, get out of its path immediately.”
Well, you can at least try. A typical dry snow avalanche moves at about 80 mph—trying to outrun it or escape its path is nearly impossible.
There may be some opportunities for high-speed snowmobiles, but for others, the chances are slim. Similarly, avalanches that occur at high elevations rarely harm people below.
Yet another unbreakable record: 90% of avalanches are triggered by the victim or someone in the victim’s party.
"Drownings often happen to good swimmers."
We’re happy to report here that the opposite is true. Experienced avalanche professionals have an extremely low avalanche fatality rate compared to others. Less than 1% of avalanche fatalities involve avalanche professionals.
"Spit to see which way is up."
It doesn’t matter which way is up anymore. Once buried under an avalanche debris pile, you don’t have a chance to dig yourself out — you’re buried as if in concrete. Only your friends can dig you out.
The most common question,How fast do avalanches travel?
Dry slab avalanches typically move at speeds of 60–80 miles per hour, reaching that speed within just 5 seconds of release. Wet avalanches are much slower, moving at about 20 miles per hour.
Which type of avalanche is the most dangerous?
Dry slab avalanches account for almost all avalanche fatalities. A slab avalanche is like a plate sliding off a table — a cohesive slab of snow breaks away from a weaker layer beneath.
The slab shatters like a sheet of glass, and victims caught in the middle usually have no chance of escape.
What causes slab avalanches?
Snow is a lot like people — they don’t like sudden changes (just like no one notices when taxes go up slowly). Dry slab avalanches occur when a weak layer beneath a slab collapses, usually because too much weight has been added too quickly for the weak layer to support. Snow is very sensitive to the rate of stress change. Two feet of snow that has been sitting for two weeks is no problem, two feet that fell two days ago might be trouble, and two feet that accumulated in two hours is a huge problem (wind can easily deposit two feet of snow in just two hours). So, the weight of a single person can put tremendous stress on that weak layer below — not over the course of two hours, but in a fraction of a second. That’s why 90% of avalanches are triggered by the victim (or someone in their party).
What kind of weather conditions cause avalanches?
Wind is the most common cause of avalanches. Wind can deposit snow up to 10 times faster than actual snowfall. Wind blows snow from the windward side of obstacles and deposits it on the leeward side. We call this “wind loading.”
Additional weight from new snowfall can also trigger avalanches if it accumulates faster than the weak layers below can support. Rapid temperature increases can also trigger dry snow avalanches, though this is less common.
Rainfall or surface melting of the snowpack can also lead to avalanches. For example, rain and new snow often trigger avalanches quickly, while strong sunlight and rising temperatures can melt the snow and lead to wet avalanches.
Wet avalanches occur when meltwater reduces the cohesion between snow grains in the weak layer, leading to a loss of support. But wind, snowfall, and rising temperatures don’t always cause avalanches.
It also depends on the existing snowpack conditions and other factors. If the existing snowpack is very stable, even heavy wind-loaded snow can bond well with it and remain safe under certain conditions.
Assessing snowpack stability is a complex process that requires extensive knowledge and experience to develop strong avalanche stability evaluation skills.
Who are the victims of avalanches?
Avalanche victims are almost always outdoor recreationists: snowmobilers, climbers, snowboarders, skiers, snowshoers, or hikers. Snowmobilers have the highest fatality rate.
How do people die when buried in an avalanche?
The good news is that even the densest avalanche debris contains 60–70% air, but that’s not the problem. Victims usually die from carbon dioxide poisoning caused by a rapid buildup of CO₂ near their mouth and nose.
Statistics show that 93% of avalanche victims dug out within 15 minutes survive, but after 15 minutes, the numbers get grim. After 45 minutes, only 20–30% survive. Beyond two hours, no one survives. So, you don’t have much time.