Turnagain Pass

A skier or snowmachiner triggering a deep slab avalanche 2-4+ feet thick remains a very real and scary possibility.  Strong Northwest winds over the last three days have been loading a variety of aspects and scouring ridge lines. This wind direction can funnel through Turnagain Pass and cause unusual loading patterns opposite of our normal Easterly storm tracks. If you’re out hunting for soft snow, be aware that dozens of large human triggered avalanches have occurred over the last 10 days across our region (Seward to Girdwood) including a large avalanche triggered remotely by a helicopter on Tuesday in Girdwood. Knowing where in the terrain a large and destructive avalanche could be triggered is a difficult question. It may be the 10th person onto the slope that finds a thin part of the snowpack (a trigger point) or it could be a person triggering a slab remotely on an adjacent slope or below. There is a lot of uncertainty around this avalanche problem due to well preserved and widespread buried surface hoar and facets under a thick, connected slab 2-4+ feet thick. This structure has been found at all elevations and on all aspects. Daily warming and radiation from the sun can make it easier to trigger in the afternoons and evenings, especially if winds are calm. 

With a deep slab problem it is important to remember no signs of instability may be present before a slope releases.  It is crucial to visualize the consequences if the slope does slide. Are there terrain traps below?  Bigger slope = Bigger avalanche. Thin spots near rocks and along ridgelines are likely areas to find the trigger point.

A large avalanche was remotely triggered by a helicopter in Winner Creek near Girdwood on Tuesday. This avalanche was triggered from 1/4 of a mile away at 2500′ and released on the layer of weak faceted snow on a slick crust that has been the culprit in most of the avalanches over the past week. 

A natural slab avalanche on a Northeast aspect of Raggedtop Peak in Girdwood at 3800′ was first seen on Tuesday morning, but it’s unknown when this avalanche released.

Wind Slabs: Be aware of newly formed wind slabs on a variety of aspects due to unusual wind loading patterns and cross loading from strong Northwest winds this week.  Smooth supportable surfaces where the snow is hollow sounding are suspect, especially if the slope is unsupported. Look for cracking and identify terrain features with a pillow-shaped look where triggering a wind slab could break above you. Warming from the sun can make triggering easier in the afternoon, and a wind slab could step down to older snow and create a much deeper and more dangerous avalanche.

Cornices: Cornices are large and looming and the sun and above freezing temperatures can make them more unstable. Give these an extra wide berth and limit exposure underneath them.  A cornice fall could trigger an avalanche on a slope below.

Strong NW winds moving snow around on Tincan Tuesday.