Over the past month I've been watching the snowpack very closely--both while guiding earlier in the month and now producing the Public Avalanche Forecasts for the Canadian Avalanche Centre for the past week or so.
There has been a steady and escalating series of incidents in the last 5-7 days. Skiers have been and continue to accidentally trigger avalanches and in many cases, are getting caught in the slides they trigger. So far, everyone has been lucky and has escaped without serious consequences.
In the last 48 hours I'm aware of the following notable incidents:
- A size 2.5 avalanche which had extensive old tracks in the bed surface.
- A three-person, partial burial involvement with non-life-threatening injuries to one skier in a size 1.5
- A size 2 skier triggered soft slab that propagated through an area below a steep cliff that generally sees a lot of self-stabilization from sluffing.
- A partial burial when a skier accidentally released a slide onto his partner below.
- A snowmobiler who triggered a slide, was fully buried, and was rescued by his partners.
- A size 3 skier triggered avalanche that ran to valley bottom, "snapping trees" as it went.
These are just the notables. There are numerous other human and natural triggered avalanches that make for several pages of data from the last couple of days. These events were largely in the
This is a classic scenario which, in the past, has often culminated in an unfortunate and serious accident.
The avalanches and incidents we are seeing have been on a variety of aspects and elevations. The details would require an extensive discussion but, in brief, the avalanches we have seen involve storm snow interfaces from the last snowfall and wind event as well as several crust, facet, and surface hoar layers which formed in late January/early February and then were subsequently buried between Feb 2 and Feb 8, depending on location. Since Feb 10th or so a metre or more of new snow has further buried the early February layers.
It's an extremely tricky situation in the Cariboos, Purcells,
I've been in the avalanche business for over 25 years and it's been a long time since I've seen a condition this complex and variable. In the last 24 hours, the words "low confidence", "spooky", "tricky", and "suspicious" have been used in relation to snow stability and avalanche hazard. It's seldom that people actually take the time to pick up the phone or write us an email about conditions, but there's an increasing number of calls and messages coming in to the CAC office; a very real indication of concerns and a desire to get the message out about the problems we are facing.
We are now entering a period where things are going to start looking better. Cool temps, reduced winds, and lack of new snow will cause a slowing of and perhaps will even stop significant natural activity. Human-triggering of avalanches will become more sporadic and difficult.
However, I urge everyone to remember the underlying condition still exists: storm snow instabilities in the alpine and wind affected areas will linger for a day or two yet. And the early February layers bring to mind the immortal words of Monty Python: "he's not dead—he's just sleeping." You most definitely do not want to tickle the deeply buried instabilities and have them wake up on a slope your are riding. There's now up to 120cm of snow available to avalanche on these layers and that snow is settling into a firmer slab layer that could well propagate much farther (making for larger, more destructive avalanches) than what we've seen in the slow, subtle, and steady buildup over the last 7-10 days. The size 3, skier triggered avalanche that ran to valley bottom yesterday is evidence of just this kind of condition.
The biggest problems we are dealing with are deeply buried, persistent weak layers. While the low elevation surface hoar is getting much of the attention, I think in some cases the February layers have not yet begun to perform to their maximum potential (facet layers in the alpine for example?). In some cases these persistent layers will almost certainly hang around for some time yet, napping for a while then waking up with new snow, wind, temperature changes, strong solar radiation, or if the right human trigger comes along at the right place and the right time.
I may be (and hope) I'm wrong, but am concerned we will see increasingly large avalanches on slopes that have been previously tracked up, on moderate angled slopes which have not yet avalanched in the most recent cycle, at low elevations on surface hoar layers, at higher elevations on old facets and crusts (even after current storm instabilities settle out), and in the trees where even a small slide can produce serious consequences if you get raked through the timber.
I think we are in a period where we all need to think very carefully about what we are doing and why we are doing it. Here's some things I think can help decrease risk—this is what I'll be doing when I head back out into the mountains next week:
- Be very cautious in areas where you do not have good local knowledge about past use and avalanche history of a slope; you probably need to know what's happened since about Feb 2 anyway.
- Choose safer terrain with options for travel on:
- low angle slopes (less than 25 degrees),
- in dense trees,
- on smaller open slopes, and
- away from terrain traps such as creeks, gullies, cliffs, and sudden transitions from steep to flat.
- The best choice, if you insist on riding more aggressive terrain and do not have local knowledge, is to ride on slopes that have avalanched recently and are not yet reloaded with new or wind-blown snow (can you still see the fracture line?).
Up to about Feb 10 we experienced a great winter with generally very good stability. That has all changed and we need to change our thinking and our approach for the next while and perhaps for the rest of the winter if we are to come out of the season unscathed.
Post to/read the ACMG Mountain Conditions Report (http://www.acmg.ca/mcr/default.htm) and on the Canadian Avalanche Centre's public forums (http://www.avalanche.ca/Forums/), talk to your friends and others while out in the mountains, feel free to forward this to others, and go ahead if you want to post this in other public forums; we need to get the word out. Given the spate of incidents that doesn't seem to be slowing down, I'm worried that folks aren't getting the message or seeing the trend.
These are my personal thoughts and do not necessarily reflect the opinion or position of my employers or the professional organizations of which I am a member. Your comments and feedback are welcome. Feel free to email me: kklassen@avalanche.ca if you think I'm dead wrong, if you have information that is of use in helping others, or if you have data that supports these ideas.
Safe travels.
Karl Klassen
ACMG/IFMGA Mountain Guide
Public Avalanche Forecaster, Canadian Avalanche Centre