Turnagain Pass

A strong outflow wind event triggered a handful of natural wind slab avalanches across our region yesterday. Most of these occurred in Summit Lake, but one was seen near Bertha Creek on Seattle Ridge and one on Max’s Mountain in Girdwood. Northwest winds averaging 20-40mph were seen drifting snow along many ridge tops. This wind direction creates unusual wind loading patterns opposite our normal Easterly storm track direction. Aspects that are shallow and wind scoured will be more loaded than usual. Another challenge is Sunburst weather station is sheltered from this wind direction and not necessarily representative of the full extent of this wind event. For comparison a weather station along the Alaska railroad corridor, South of Grandview, recorded NW winds 30-40mph with gusts in the 60mph’s most of the day. Keep this in mind if you head into the mountains. Hard supportable snow should be suspect and can release once well onto a slope. Wind slabs could be small and shallow or larger if they step down to older weak snow. Northwest winds have backed down overnight, but will remain Moderate, 10-25mph at higher elevations. Any active wind loading or shooting cracks will be obvious clues wind slabs are still tender. 

CORNICES: Cornices are looming large in some of the Alpine terrain. Yesterday’s wind may have added additional stress. Give them an extra wide berth as they often break farther back than expected.

A wind slab released sometime yesterday afternoon on Max’s West face in Girdwood Valley. This avalanche was likely human triggered, based on the ski tracks above and below, but those details have not been confirmed. 

Yesterday’s wind event added stress to older weaker layers within our existing snowpack. This was the case in Summit Lake where several avalanches released near the ground in shallow snowpack zones on East facing aspects of Summit Peak. In deeper snowpack zones, like Turnagain and Girdwood, a wide spread layer of buried surface hoar sits 1-3’ below the surface. For those just tuning in, the MLK buried surface hoar (buried on Martin Luther King day) was the culprit in numerous human triggered avalanches over the last two and half weeks. The last human triggered avalanche occurred 8 days ago on Eddies, remotely triggered from a ridge onto a steep, unsupported slope. The question remains, can person or snowmachine tip the balance? At this point the jury is out, but due to the nature of buried surface hoar and yesterday’s wind loading event, this layer is still suspect.

Keep the MLK surface hoar in mind and remember:

1. This weak layer is widespread in the region and seems to be particularly suspect between 2000′-2500′ due to a melt-freeze crust associated with it.
2. Use safe travel protocol. Expose only one person at a time (this includes paying attention to other groups in the area), watch partners, stop in safe zones and be rescue ready.
3. Wind loaded steep features, large connected and unsupported slopes are the most suspect. As always, one can simply avoid high consequence terrain and stick to slopes under 35 degrees with nothing steeper above to avoid the issue.

Strong winds triggered several wind slabs that stepped down to older weaker snow on East facing terrain of Summit Peak in Summit Lake. Summit Lake in general has a shallower and weak snowpack than Turnagain. Areas like Johnson Pass and Lynx Creek may also harbor a similar structure.

Glide cracks are on the move and becoming more active this week. Yesterday a glide avalanched in Summit Lake and another one release in Girdwood Valley on Monday, on Goat Mountain. There are a handful of new cracks opening up including one spotted yesterday on Seattle Ridge, Repeat Offender, just South of the up-track. Several glide cracks threaten popular skin track routes on the non-motorized side of the road, like the South facing slopes of Lipps and Magnum. Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. We’ve seen glides avalanche when temperatures drop into the single digits, like yesterday, and when temperatures are above freezing. The best way to manage this problem is to identify their location and avoid traveling under their runout. This can be especially frustrating if glide cracks are opening up in popular terrain.

A glide crack opening on Seattle Ridge, on a Southeast aspect of Repeat Offender.