Turnagain Pass

Yesterday’s NYE storm (New Year’s Eve) greeted many snow enthusiasts with joy. Storm totals were 12-20″ at the mid and upper elevations from Girdwood Valley to Turnagain Pass. On the South side of Turnagain Pass, such as Sunburst and Johnson Pass, only 3-4″ of snow fell… Snowfall amounts were very different from one ridge to the other with this storm. The part of the puzzle that is not joyful however, is a layer of surface hoar underneath the new snow. This has created poor bonding between the new and old snow; proved yesterday by the plethora of human triggered avalanches. To make matters a bit worse, under the surface hoar are near surface facets (another weak layer) and then a hard layer of crust or wind packed snow that is acting as a bed surface. All these ingredients point to likely human triggered avalanches. 

There is another storm headed in today. An additional 5-10″ of snow is expected with another 6-12″ tonight above 1,000′; rain/snow line should be around 500-700’. This will increase the load on the weak layers as well as the slab thickness to over a foot and up to 3′ in places. The storm is coming in warmer and windier, which will also contribute to the increasing avalanche danger. Even small(ish) slopes could become hazardous if the slab is 3 feet thick instead of 1 foot. Keep this in mind if you are headed to the backcounty this week. Also, keep in mind remote triggering is possible from the side or below a slope. Steering well clear of runout zones will be key.

Yesterday’s avalanche activity:
Human triggered avalanches were widespread in the Tincan Trees yesterday. All avalanches were soft slabs or wind slabs around 1-2′ thick and failing on the buried surface hoar mentioned above. Photo below and comment from a group that triggered a larger avalanche in the Tincan Trees (16″ deep, 150 wide and running 200′ ). Triggered remotely by 3rd skier on adjacent slope – no one caught.

“We were pretty surprised at how much energy and how far it ran through trees.”   (Photo Ray Koleser)

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Photos of skier triggered soft slabs in the Tincan Trees yesterday. Smaller terrain, smaller slab, smaller avalanches.  (Photos by Trip Kinney) 

Shooting cracks

A look at the new snow sitting on weak layers with a harder wind packed surface below. All known avalanche activity seen yesterday on Tincan was due to the buried surface hoar.

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In the alpine, above 3,000’, rapidly loading slopes may awaken a large and dangerous deep slab avalanche. At these elevations, a hard slab, 3-5+ feet thick, is sitting on top of weak sugary snow (basal facets) near the ground. As new snow increases the load over this snowpack structure during the current storms, there will be the potential for large natural avalanches. Between storms, human triggered deep slab avalanches will be possible. This is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. Keep this in mind as breaks between storms may allow for travel to the Alpine.