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Just returned from a week on the east side of the
Selkirks just north of the Trans-Canada highway.
Weather:
We had very light snowfalls that accumulated 5 - 10
cm of cold, fluffy, dry powder over the week. Temperatures were cold--warmest
about -6.0 in sheltered, sunny locations at treeline with the coldest being
-19.0 this morning after a night of clear skies. Cloud cover was a mixed bag
from fully overcast to clear--nothing lasting more than 12 hours or so. Winds
were light and variable although I did hear some stronger winds for a few hours
two nights ago.
Snowpack, in general
terms:
The snowpack depth and layering is extremely
variable over elevation and terrain features. Higher elevations and exposed
terrain features were hammered by very strong winds from variable directions
about 2 weeks ago and we found very, very hard crusts and surface slabs as well
as hard sastrugi. Winds also penetrated into the trees creating crusts and
thin slabs. Where there was little evidence of wind affect (below treeline,
sheltered areas) a strong crust or thin slab exists (the most recent warm
snowfall frozen hard by cold temperatures?). All this lies under the 5-10cm of
fluff mentioned above.
Snowpack, more
specifically:
In the low alpine (around 7500 feet) we found a
160cm snowpack on the lower end of the local glacier. The weakest layer in the
entire pack here was a 5cm thick layer of facets (sugary grains) right on the
ice. Above this was a 40cm mix of facets and crusts--the November layer(s) that
dominate the deep snowpack in much of BC and Alberta this year. The middle
of the alpine snowpack is mostly faceted snow with the various weak layers from
early and late December clearly visible but mostly quite firm and reasonably
well bonded. The upper snowpack is a mixed bag of slightly weaker and stronger
layers, none of which showed much indication of instability for the moment. The
January 27th surface is visible in the alpine under about 25 - 40 cm of very
hard (Knife resistance--almost as hard as a well tilled slope at the ski hill)
slab with a dusting of new snow on top. The surface slab seems reasonably well
bonded to the January 27th surface for the moment.
At treeline (around 6700 feet) we found 100 - 150
cm of snow. Under the 5 - 10cm of fluff lies a 20 - 40cm very hard
wind or settlement/temperature crust/slab. Pretty much the entire remainder
of the snowpack is faceted and the facet/crust combos from November are easily
recognizeable near the ground. The top layer, at the moment, seems fairly well
bonded to the underlying facets. Failure did occur at the top of the November
layer but the nature of the failure suggests it was unlikely to be triggered by
a skier in this location, where the weak layer is over 100cm down.
Below treeline, the snowpack thins rapidly to
perhaps 70-80cm with a thinner crust/slab on the surface that carries a skier
(mostly) and weak facets below. While we did not see it, neighbouring areas were
reporting surface hoar (feathery crystals) in the upper part of the snowpack
below treeline.
Avalanche Activity:
Other than a few small loose dry sluffs and a
couple of thin, soft slabs (all on quite steep terrain) we saw no avalanche
activity. Small skier-triggered slabs were reported in nearby areas, failing on
surface hoar in below treeline locations.
Travel:
Tracksetting was tricky with the very hard
surfaces. The bit of fluff on top did little to make it easier although it did
seem to get a bit better the last couple of days (maybe my skinning technique
just got better?). Ski crampons would be helpful until things change. We found
decent skiing on moderate, sheltered alpine terrain where it was easier to
set an edge in the hard snow beneath the 5 - 10 cm of new snow and where there
was no hidden sastrugi lurking. At treeline, if you break through the surface
slab, you sink boot-top or knee deep into the facets below. Below treeline you
sink almost to the ground in many places if you break through.
Hazards:
Crevasses: coverage on the glaciers is highly
variable and generally below normal in this region.
Sliders on hard surface layers: kind felt like
spring touring sometimes, where the potential for a long slider on a hard,
smooth surface is a concern.
Avalanche: My primary concerns are the weak basal
layer in the alpine and the generally weak, faceted mid and lower snowpack at
and below treeline. The likelihood of triggering an avalanche in this area at
the moment is quite low. However, there is potential for large, destructive
avalanches in the alpine if something were to trigger that deep layer. At and
below treeline, there's not much of a load or a slab on the facets--yet--so not
much hazard at the moment.
Terrain and Risk
Management:
On the glaciers I stayed on fairly benign
terrain: compression zones where crevasses are less likely and low ground
where the wind had drifted snow in a bit deeper.
On steep ground I'd consider taking skis off and
kicking steps, using ski or boot crampons, or just plain slowing down and taking
extra care on uptracks if traversing or turning. Have well tuned skis with sharp
edges for downhill runs on steep slopes to handle the "pow on
pavement"!
In the alpine I stayed out from under large, steep
slopes. I chose minimize or eliminate where possible, exposure to slopes that
had potentially large triggers above, figuring it would take something like an
icefall, cornice fall, or a small slab or sluff from steep cliffs above to
trigger one of those deeply buried persistent weak layers, the one of greatest
concern being the basal facets on glacier ice. At and below treeline, I
skied cautiously if I encountered a steep, convex or unsupported slope.
The existing snowpack, while apparently quite
stable at the moment, does not inspire much confidence. The current
surface is setting up to become another persistent weak layer of facets or
perhaps surface hoar on a very firm slab/crust when it gets buried. I'd be
extremely careful if/when the weather changes. Warming temperatures, strong
solar radiation, any significant snowfall, or any kind of windloading event
would be of concern. Certainly any of these weather changes will increase the
sensitivity to triggering of any one of a number of weaker layers now in the
snowpack, more so if more than one factor occurs at once. If/when the weather
turns, I'd throttle back pretty heavily and stay away from avalanche terrain to
see if the current surface holds. After the weather becomes more benign,
I'd give it a couple of days before stepping out again to see if the
deeper, persistent weak layers might reactivate.
Karl Klassen
Mountain
Guide
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