Skiing big terrain in winter in Colorado during considerable avalanche danger!?!? What can we make of skiers ripping big lines in winter during moderate or considerable danger when we have persistence on the problem list?
First thing is to keep in mind that you don’t know what they know or what went into their decision making process. We should always keep an open mind and not pass judgment too hastily. I can’t comment on any decision making that I am not part of, so I figured I would share some of my own thought process in an instance like this where we skied a 1500 foot steep SE facing couloir in Rocky Mountain National Park in early January in deep snow when most of the state was at considerable danger and SE aspects were on the problem rose.
Two Pathways to Understanding Avalanche Hazard
There are two pathways to understand avalanche hazard. 1) We can dig a snowpit, observe the stratigraphy and speculate on the mechanical interactions of the layers that might produce an avalanche. 2) We can look at a piece of terrain and say: in 35 years of people regularly skiing here no one has observed an avalanche of this type in these conditions. We can also look at all the avalanches that have happened recently in the range and say, well none of those avalanches are in terrain that looks like this.
These two pathways are best when used in conjunction. We can use the snowpit speculation to validate if the conditions fit into the larger history of an area and allow us to rely more heavily on our assessment of the history.
Specific Terrain Considerations
When it comes to the decision to ski the Dragon Tail, we need to step back to some key concepts around the formation of continental style basal facet persistences. The idea of confined and unconfined terrain is useful with this kind of problem deeper in the snowpack and is rooted in our historic knowledge of these kinds of avalanche cycles. After a significant cycle on a deeper basal facet persistence, we tend to find the snow in the narrow confined couloirs intact and the unconfined aprons below them ripped to the ground.
There are a couple of speculations we can make on the mechanical reasons for this and they primarily focus on terrain specific effects that disrupt the formation and continuity of the basal facet layer.
When we have large rock lined couloirs, the walls and adjacent slopes produce a large amount of sloughing on a regular basis. This has a substantial effect on the disruption of the formation and continuity in any faceted basal layers.
In Rocky many couloirs sit on the north and south faces of long east west facing valleys. These glacial valleys are giant wind tunnels and lead to an extremely irregular snow deposition environment. We don’t get clean transport and deposition zones we have a ton of giant snow tornadoes and super irregular wind transport.
The bed surfaces in these steep confined couloirs can range, but in many cases they are exceptionally rough with large geometries and little in the way of planar ground surfaces. In many cases we may end up with a fair bit of rotted snow but the supportive wind packs slabs are not resting on this snow; they are resting on big boulders and the sides of the couloir.
This combination of factors add up to make it very hard for basal layers to form in a fashion that can produce avalanching on the basal layers. It makes it hard for a basal facet layer to form at all, and if it does form it isn’t in a way where it is actually supporting the wind packed midpack slabs. Even if some parts of the terrain can form this way the chances of it maintaining any continuity across larger portions of a start zone is extremely low.
The historic data supports some combination of these factors playing a roll as the result is observable: lack of this kind of avalanching.
The aprons below the couloirs are a different story though. This is the place I am indeed most worried about this kind of problem. This is the unconfined terrain where we see these kinds of avalanches go big! So what mechanisms are at play that help prevent the formation and continuity of basal layers in these specific features in Rocky?
I think a lot of it has to do with the wind. They are SE facing aprons that get smashed by the super irregular wind characteristic of Rocky’s geology. In these apron features the wind leads the snowpacks basal layers to consist of irregular overlapping lenses of transported snow. With large boulders sticking well into the midpack. The sun plays a roll as well. There are only small sections that are on the steeper side as well. That being said, even a irregular and discontinuous mix of crusts and wind drifts could begin to facet into a fairly continuous shit basal layer that with sufficient loading could conceivably produce some big avalanches.
Once again these are just speculations, but the reality is we just have never observed a basal facet avalanche in the apron below the Dragon Tail in 35 years of people skiing in this area on a regular basis—Or I should say, I have never heard of it. If any one has a picture of this I would love to see it.
What was our decision making process?
When it comes to our decision to ski the line, we didn’t really consider it early on in the day. We were planing on skiing in the trees where the wind wouldn’t have gotten to the snow. We didn’t really consider going up higher as the wind ruins the snow pretty much all the time. However, after a lap in the trees above dream lake we could see there was really high quality snow up higher without any wind and thought it was worth taking a look.
Now I wasn’t convinced we would want to do anything more than go look—this has been one of these challenging seasons with well developed basal facets and fairly significant and settled midpack slab from the substantial snowfall during early jan storm cycles. This season could very much be viewed as atypical, or at least on the more concerning end of typical. This kind of setup means it’s key to not be too reliant on historical trends.
What we saw on our way into the area was the remnants of a fairly substantial wind slab that had flushed the couloir maybe three days prior and when it impacted the apron produced some extremely localized and resistant fracturing in the basal zone. Basically the thing had experienced a significant trigger and couldn’t really produce the widespread propagation we are worried about in a large unconfined slope.
So the prospect of ripping a mega classic line in about the best snow conditions you could have on earth was enticing enough to put in a knee to waist deep boot pack!
With waist deep trail blazing there are some concerns about a more substantial surface avalanche in storm or wind snow.
The key to these problems though is the rate and duration of loading. We had pretty much an ideal setup. We were coming out of a week upslope event and had been experiencing very little wind the last few days with just a few inches of snow here and there.
Because we were only getting a few inches a day for the last week it was settling well into really nice skiing. I don’t really need to know more than the weather history and the feeling of the surface snow under my boots for this kind of problem so game on.
Did we make the right choice? Was it worth it? Only you can decide if the risk is worth the reward. Always keep in mind: with avalanches the moment you really think you have it figured out they might do something weird and totally catch you off guard. Check out the instagram post for more images of the terrain.