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 Columbia Mountains but also include the Northwest
and Purcells. If we go back a few days, pretty much all other regions have seen
similar events. And these are just the ones I personally know
about.
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, Columbias, Northwest (North Coast
and inland coast mtns), South Rockies, and to a
growing extent, in the Kootenay-Boundary region. The South Coast appears better?maybe someone with
local experience of what?s going on there can comment. I suspect that areas with
a warmer, wetter climate (e.g. coastal areas) will improve more (and more
rapidly) than interior ranges. Again, some local commentary would be welcome. I
suspect that this condition is just starting to develop in the main ranges of
the Rockies where the February layers exist but are not yet as deeply buried so
do not have the load or slabs that we are seeing elsewhere--perhaps less low
elevation surface hoar there? any locals willing to
comment?
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@xxxxxxxxxxxx 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