[MCR] Large unexpected avalanche in the Rockies

Just a heads up for folks that are still out in the backcountry. Parks
Canada avalanche forecasters received a report from a very experienced
party yesterday of a large remotely triggered deep slab avalanche in
Kootenay National Park. This avalanche was out of character with the
conditions we have been seeing in Banff, Yoho and Kootenay lately and was a
surprise to the forecasting team as well as many avalanche professionals in
the area.

It was on a SW aspect between 2650 m and 2100 on Mt Whymper. It
occurred at 1230 as a group of three entered a thin snowpack area as they
finished bootpacking a steep section to the Whymper high col. They had been
bootpacking up a supportive 10cm thick melt freeze crust and feeling
confident in the slope stability. Temperatures were cool (-5) and mostly
cloudy. Just before they triggered the avalanche, the sun had popped out
and the solar radiation was intense for a short time, although this didn't seem to have any affect on the crust. As they approached the col they heard a whumph, and a
few seconds later they saw the slope they had just bootpacked rip out to
ground, size 3.5.

Parks Canada forecasters went on a field trip today to check out the slide.
The debris field was 200m by 500m and 1-3m deep with hard, blocky debris.
See pictures of the avalanche here.

This event seems to be an anomaly, and we don't expect widespread avalanche activity on this layer until we get a significant warm up. However, this event indicates that it is still possible for a skiier/climber to trigger the deep basal facets and although the probability of triggering is low, the consequences are huge.  Just because you have a strong, supportive surface crust, doesn't mean you can't trigger the weak layer from a thin spot.

Keep this event in mind as you are skiing in the Rockies this spring.

Stay safe!

Parks Canada Visitor Safety Team

Banff, Yoho & Kootenay National Parks

www.parksmountainsafety.ca

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