We thought we would start this tread as a place to put down some of our thought and ideas that don't really fit in our regional conditions threads. Please feel free to engage in discussion and share your thoughts, questions or comments.
A key part to understanding any avalanche problem and
planning how to manage it is to understand the distribution of the offending
layer or interface in the terrain. We
often talk of avalanche problem being widespread, confined to specific terrain
or isolated. From the questions people
have been sending us recently it seems there may be some confusion about what these
terms actually mean.
Any avalanche problems weather widespread, specific or
isolated will be distributed across a wide area
Digging multiple pits in a small area today reminded us just
how variable the distribution of the Febuary 21st surface hoar layer
can be. We managed our hazard by
choosing a low angle slope to dig on.. Within
100m we dug three pits on a North East aspect.
In our first pit we found a well-preserved layer of surface hoar 80 cm
down and reactive. 50m across the
slope the surface hoar was there but smaller and starting to settle into the
slab above, here it was reactive only under very hard loads. 50 m
in the other direction the surface hoar was nowhere to be found.
While all these pits were dug on a feature with fairly uniform
terrain characteristics I suspect that the presence or absents of the surface
hoar in the individual pits is due to small variations in the amount of wind
and sun the surface the snow was exposed to back in mid February when this
layer was developing. Characteristics
impossible to identify now.
In the last avalanche cycle we saw that where this layer
exists it is capable of producing large and destructive avalanches. Nothing since then has made me think that
this is not still the case. At an
average depth of 80cm this layer is approaching the limits of what is
susceptible to human triggering. However, given its isolated nature sledding
or skiing on these N - NE aspects is analogous to walking through a mine field: you might make it through no problem; on the
other hand you might not; and then, BOOM!
After weeks of
chasing this layer down I’m still not confident I have it figure out. As hard is it is to not jump onto those
tempting north facing slopes avoiding them is the only technique I know of how to
mitigate this problem. Digging a pit and
not seeing surface hoar is no guarantee of safety. Personally I look forward to may years of skiing and high marking chalky North aspects so resisting the lure of the minefield is
going to by my strategy until I start seeing strong evidence that this layer
has been assimilated into the mid pack wherever it exists.