Yesterday, wardens toured up Napoleon Spur searching for the distribution
of the February 4th surface hoar layer. We found surface hoar in the
snowpack down 25-30cm, and were able to trace it from the valley floor
(1100 meters) to our high point at 1850 meters. The surface hoar was
reactive at higher elevations, but resistant planar in character (CTM13,
RB6). It was far more reactive at lower elevations, and we were able to
ski cut several small sluffs, and a size 1 soft slab avalanche from a
convex roll that ran far and fast into a gully. This was at 1245 meter
elevation. The surface hoar here was 15mm in size, and very well
preserved.
Today, U of C researchers were on a similar mission, looking for the
surface hoar. They found it to be very reactive in the Bostock drainage,
and were able to ski cut a soft slab. They were at 1470 meters, on a NE
aspect, on a convex 30 degree roll. The slide failed on surface hoar down
35 cm, was 40 meters wide, and ran 150 meters long.
To summarize, the February 4 surface hoar is somewhat sporadic in
distribution, but it seems very prevalent in protected areas at and below
treeline, especially on north and east aspects. The snow on top of this
layer is starting to get firm enough to propagate as a slab, and is the
ideal depth to be triggered easily by skiers. The words "tip-toe" come to
mind for travel below treeline, especially in open glades or gullies.
Sylvia Forest
Mountain Guide
Glacier Park
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