This year has been fairly unprecedented in the number of avalanche accidents around the world. From the alps, to the Untied States up into Canada. Why is headline after headline another avalanche accident?
Colorado Everywhere
A Colorado snowpack everywhere—well, what we refer to as a more continental snow climate everywhere—characterized by irregular snowfall with prolonged high pressure periods.
During these high pressure periods the snowpack undergoes dramatic temperature swings on the snow surface, in a process called diurnal recrystallization. During these temperature swings, water vapor is drawn through the top few centimeters of the snowpack and causes the snow grains to become weak. This weak surface then becomes the cause of an avalanche after new snow begins to fall.
Diurnal Recrystallization
Every day when the sun warms the mountains, that warm ambient temperature soaks into the top 20cm of the snow. It doesn’t get so warm it melts the snow but it brings the temp up closer to freezing. Then when night comes, and the sky is cloudless, the snow can emit long wave radiation into the atmosphere.
This long wave release is a key feature of weak snow formation. When there are no clouds to bounce the long wave radiation back to the surface, the snowpack cools dramatically. It’s the reason you’ll find the snow surface frozen in the morning after a clear night, even if the ambient temperatures didn’t get below 40 degrees.
Each night there is relatively warm humid air in the top 20cm of the snowpack and extremely cold dry air on the top 3-5 cm because of the long wave release. The warm humid air holds higher vapor content than cold dry air. When we have a difference in vapor pressure across a permeable membrane we get vapor transport.
You may have heard it called a temperature gradient, it’s really a vapor pressure gradient caused by different temperature air, holding different vapor contents.
When the water vapor flows across this gradient—heading toward the surface—it works its way through the snowpack jumping from snow grain to snow grain. During this process of jumping, the water molecules stick back into place based of the polarity of the water molecule and align into a crystalline structure. This ‘faceted structure’ becomes the foundation onto which a new storm falls.
The more diurnal cycles, the worse the facets and the worse the foundation.
It’s not because the snow is weak it’s because its unusual
In a continental snow climate like Colorado, we are used to dealing with these persistent weak layers. How we ski, and what terrain we go into with these types of avalanche problems is much different than how we ski in an area without them.
While this season in Colorado is pretty bad, it’s is not really that different from many seasons in the past, and typical travel strategies work as good as they ever do. But in an area that is not used to having these weak layers, the way people ski needs to change dramatically from the status quo.
In a more ‘maritime’ or ‘intermountain’ areas, the weather is much snowier and new storms come quickly. There is not much time for these weak layers to grow during clear weather. The normal avalanche problems in these areas typically disappear quickly and require much steeper terrain to produce avalanching.
These are areas like Utah, the Sierra, the Tetons and many parts of the Alps. All the areas that are experiencing a really significant number of bad accidents.
In these areas many skiers are not adapting their skiing to the changing conditions. Areas that were usually very stable—because of constant snowfall and short periods of high pressure, are no longer a safe place to ski. Adaptation to the uncharacteristic snowpack is key.
Institutional risk management vs adaptive risk management
Using the local ski community’s ‘institutional’ and collective knowledge of where is a safe or unsafe place to ski, can be a real asset. If people have been skiing in an area for 50 years and never seen an avalanche there, that means a lot. Especially to someone with out the significant training and experience needed to make a stability assessment themselves. So much of understanding avalanche danger is recognizing the patterns of where and when they happen.
However, this strategy falls apart when conditions are different than they have been in the last 50 years, and unusual avalanches can occur. If we don’t adapt our approach—and ski like we are in Colorado—we can get caught off guard.
This is sometimes referred to as the familiarity heuristic bias.
Don’t get me wrong, institutional knowledge about where avalanches happen is a very powerful asset, but it can also be very dangerous if not used with the appropriate lens. It works if the weather and snowpack patterns are the usual patterns, but falls apart quickly when the patterns shift.
In some ways you could point to this as a reason for many unusual accidents the past few years. Take the inbound avalanche fatality at Palisade in 2024. The ski patrol detonated many charges in the avalanche start zone, as prescribed by their mitigation plan. This is generally very effective at managing the storm and wind slabs typical of that start zone.
However, they were not managing storm and winds slabs in this case. They were managing an extremely deep persistent slab formed by a high pressure period and a adapted strategy was necessary. The usual shot placements were not effective. Targeting the areas that typical avalanches start would mean targeting the thickest part of the avalanche—where the slab was so thick the charges merely put dents in it. An adaptive strategy would mean targeting areas that would be ineffective to mange normal avalanches. You would want to target the much thinner portions of the slope below the typical start zone.
With the unusual conditions, an institutional risk management strategy becomes far less effective and even misleading. We don’t know exactly where shots were placed in this case, as that kind of information isn’t released publicly, but a skier was able to trigger that slab, full of blast marks by skiing through a thin spot below the usual start zones. Was this a institutional failure or truly a freak accident? Unfortunately we may never know as in these kinds of accidents the records–usually copious–are buried by the lawyers.
The Remote Trigger
The other feature of these persistent weak layers are the ability to remote trigger. New snow related avalanches—the storm and the wind slabs—you generally need to be on the avalanche to trigger it. In many of these areas now experiencing these bad accidents they never have to concern themselves with a remote trigger.
The remote trigger is common with many persistent avalanche types. Essentially, the weak snow under the slab collapses and would result in an avalanche—but—the slope is not steep enough for the slab to begin sliding. This collapse doesn’t just stop in the flats though, its spreads out from the skier and when it reaches steeper terrain the slab can begin to slide.
Remote triggers are what most frequently leads to the high fatality accidents. Skiers are pretty good about spreading out and only exposing one person to the slope when its obviously avalanche terrain. When a remote trigger happens, its easy for a group of skiers to get caught as a group. This means the ability to conduct rescue is really challenging.
Many of these bad accidents results from skiers remote triggering slopes that are many times hundreds to even thousands of feet above.
The mountains are different—not more dangerous
The mountains don’t put us in danger, we put ourselves in danger by how we go into the mountains. The unusual climate patterns do cause more avalanches, but it is only more dangerous to us as skiers, if we don’t adapt.
The key is to recognize gaps in your experience. If you have not spent time dealing with the persistences we have every year in Colorado, acknowledge it and change how you go into the mountains. Recognize that you have a lot of uncertainty in your skillset given the unfamiliar conditions.
With remote triggers in particular, it often catches people that by all metrics are experienced backcountry skiers. A few years ago here in Colorado we had a bad cycle that resulted in a lot of really extreme remote triggers—even by Colorado standards. The people who were getting killed were generally 35-50 years old and had been skiing in the backcountry for 10-15 years. Well that year was the first time in ten that it was possible to create such dangerous remote triggers and the spots they had been skiing for the last decade were not the spots to be that season.
This is important for both recreational skiers and professional operations. The outdoor industry—from ski resorts to mountain guiding outfits—is generally extremely young and inexperienced as a whole. It’s a rough gig that doesn’t pay well. It’s hard and dangerous and doesn’t provide any finical or lifestyle stability. Most people can’t hang with it for very long and industry turnover is huge.
Risk management—with a generally inexperienced workforce—falls heavily onto institutional strategies. Past data and experience provides the backbone for risk management—which works great when conditions are typical, but falls apart fast when things change.
The dangerous comes from not acknowledging it.
Colorado is less dangerous this year?
Generally Colorado leads the United States in avalanche related fatalities every year, yet so far in Colorado only one person has been killed in an avalanche. Its been one heck of a dangerous season too. I would argue that a huge part of that is the backcountry community has had a lot of experience managing this type of condition compared to many other parts of the world. It’s been exceptionally bad in the alps, in particular, which unfortunately isn’t included on this chart from the CAIC.
In many ways, Colorado isn’t that much different than usual this season. The big difference is that all the erratic weather has made a lot of other places look a lot more like Colorado than ever before.
So are the mountains really more dangerous? The mountains are only dangerous if there are people there to be put in danger. The danger comes from people having experience managing what they find in the mountains or not.