Turnagain Pass

Cornices throughout the region are getting to be very large in most areas, including Turnagain Pass.  The largest natural avalanches in the last 5 days have been as a result of cornice falls.  In Haines a heli-ski guide was killed over the weekend when his party collapsed a cornice.  We got a report of a natural avalanche in the Placer river region yesterday that may have been a cornice failure.

Cornice safety relies on managing exposure.  This means you should limit the time you spend directly underneath overhanging features, especially if temperatures are warm or they are in direct sun exposure.  Traveling directly on ridge tops can be safe, as long as you give a wide berth to any overhanging sections.  When standing on a ridge it can be very difficult to know how far back a cornice might break.  In general, the breaking point is much further back than you might expect. 

The good news related to cornices is that they are one of nature’s best slope stability tests.  We get a lot of information from cornice failures when the slope underneath gets pummeled by thousands of pounds of hard cornice chunks.  Based on our observations of cornice failure, the current snowpack is showing minimal reactivity to large triggers.  This means that backcountry travelers are unlikely to trigger a slab avalanche in the backcountry today.

The one recent exception was a cornice that triggered a deep slab on the mid elevation ice crust in steep terrain in the Girdwood valley on Sunday.

Yesterday’s sunny skies were hammering southerly slopes with solar radiation.  Temperatures overall were not much above freezing, so the warming effect was minimal but still noticeable.  Some direct south facing slopes at low elevation showed a small amount of loose wet avalanche activity.

Sun is not in the weather forecast today, but temperatures are expected to reach into the low 40s at sea level.  This may be enough to melt the surface crusts and cause more minor loose avalanche activity by the afternoon.