Experts on Camera

Dr. Ethan Greene: Avalanches

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An average of 24 people per year died in U.S. avalanches over the last decade, and there were over 5,000 avalanches and 11 deaths in Colorado alone last winter.

On February 1, 2024, SciLine interviewed: Dr. Ethan Greene, an instructor in avalanche science at Colorado Mountain College and the director of the Colorado Avalanche Information Center. See the footage and transcript from the interview below, or select ‘Contents’ on the left to skip to specific questions.

Declared interests:

Dr. Ethan Greene’s work is funded by the State of Colorado and the Friends of the CAIC, a 501c3 group.

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High definition (mp4, 1280x720)




ETHAN GREENE: My name is Ethan Greene. I’m currently the director of the Colorado Avalanche Information Center and I also work with Colorado Mountain College in avalanche science—a program that they present to train avalanche workers. My background is a bit academic and a bit operational. I’ve sort of gone between the two over the many years now that I’ve been doing this. And the research that I did—at least in academia—was mostly around atmospheric modeling and modeling snow drifts and then looking at heat and mass transfer and snow and its effects on snow microstructure.

Interview with SciLine

How deadly have recent avalanche seasons been in the United States?


ETHAN GREENE: Around 26 people die in avalanches each year in the United States and that changes, of course, from from year to year. Some of the more deadly seasons that we’ve seen—at least in modern history—have been in the last few years. But if you look at the long-term record, they still don’t compare to some of the years that we saw in the late 1800s and early 1900s, when avalanches were impacting industrial sites that occupied structures. Most of the fatalities now are recreational—and so they’re still very serious accidents—but we don’t see the really large numbers of people involved in one avalanche today, like we did back in the late 1800s.

What can be done to prevent avalanche deaths and injuries?


ETHAN GREENE: Most of the deaths and injuries we see today are in a recreational setting. So, people that are mostly in the backcountry—so the vast mountainous areas of the United States—and participating in their own recreation. So, not part of a ski area, or an organized group, or a place that has a robust safety program. So, it really has a lot to do with education of training people how to take the information that’s available and apply that in the backcountry in their own setting to keep themselves out of harm’s way. So, we can do a lot with education, we can do a lot with equipment, and we can do a lot with increasing the availability of forecasts. But when it comes down to it, we really need to be in the backcountry with people when they’re making kind of small decisions about where they’re going to go, and that’s a pretty difficult task to accomplish.

What can individuals do to avoid getting caught in an avalanche?


ETHAN GREENE: What people can do to avoid getting caught in an avalanche is think about avalanches when they’re making plans for their recreational day and continue to think about them as they’re moving through the terrain throughout the day. With avalanches, sometimes very small changes in where people go can make a really big difference. So, getting current information, checking the forecast so they know what the current conditions are, looking at where they’re going to go and what they want to do for the day and thinking about how that interfaces with the avalanche conditions and making a good plan and then sticking to that plan throughout the day so that they don’t see deep powder snow that looks attractive, and lose track of all the good planning that they did earlier in the day or the day before. The next thing that they can do is be prepared for an accident. Staying out of avalanches is your best approach. But if something goes wrong, the people in your group are going to need to perform a rescue, and so having avalanche rescue equipment, an avalanche rescue transceiver, a propyl, and a shovel. Everybody in the group needs to carry that equipment, and they also need to know how to use it.

What information do we have about U.S. avalanches so far this winter?


ETHAN GREENE: What we do know is a bit more about the snow, and it’s been a very dry year across the Western U.S. We have below normal snowpack in almost every place, and we have a fairly weak snowpack because we have fairly shallow snow. That’s changed a little bit over the last month. It’s become a little bit more complicated, a little bit more diverse. But that same message, I think, still holds across the vast Western U.S.

What do avalanche forecasts tell us?


ETHAN GREENE: The forecasts that are done on avalanches really focus on a short time period. We’re really forecasting for a few hours or a few days. At the Colorado Avalanche Information Center, we do weekly outlooks, but we don’t put out forecasts longer than seven days. So, that’s really where we have the most skill and where we feel like we can make the most impact. And that timescale is really different than what you would look at for, say, a climate forecast or from a climate perspective.

How accurate are avalanche forecasts?


ETHAN GREENE: That really depends on what you consider as accurate. Right now, we’re not able to tell you exactly when. So, on the scale of of minutes, or maybe even hours, or the exact size, so maybe the portion of a slope that’s going to avalanche. But what we can do is talk about the trends of avalanches. Where they’re going to happen, the types of terrain in terms of aspect, elevation, slope, angle, location—we can do that fairly well. Our forecasts are for vast parts of Colorado, we look at the accuracy around 85% at this point.

What can you do to test the accuracy of forecasts?


ETHAN GREENE: What we can do for specific locations is make forecasts and then test those forecasts by trying to set off avalanches. And that’s what we do for transportation corridors. It’s what ski areas do for their slopes—is track the avalanche potential. Make predictions about how and where avalanches are going to release, and then move anything that we care about, mostly people, out of harm’s way and test that hypothesis by trying to set off avalanches, typically with explosives. And again, that is more of a hypothesis testing sort of approach. But it proves to be quite effective in reducing the avalanche risk to elements that are exposed to avalanche hazard.

What causes avalanches to form and release?


ETHAN GREENE: Well, there’s lots of different types of avalanches. The ones that are most deadly are called slab avalanches, where a large, cohesive piece of snow breaks off the hillside and rolls down into the valley. Those avalanches typically break at the interfaces between layers that form in the snowpack. Those layers formed through successive weather events. So, any big snowstorm, wind drifting events, or a calm period where we have no precipitation and maybe clear skies day after day, those will all form layers in the snowpack. And the interactions of those layers is what produces the avalanche potential. So, a lot of what avalanche forecasters do is identify the formation of these layers—when they’re forming and over what areas they’re forming—and then track the mechanical properties of those layers through time.

What advice do you have for reporters covering avalanches?

[Posted February 1, 2024 | Download video]