Turnagain Pass

New snow and wind loading yesterday has added weight onto a snowpack with a troublesome buried weak layer that sits 2-3′ deep. This is our primary concern today despite the surface instabilities of fresh winds slabs and sluffs in the 4-8″ of new snow. It was only three days ago that three very large and dangerous avalanches were triggered by people along Seattle Ridge. This problem layer, which is buried surface hoar, was responsible for the avalanches. That layer has not gone away and although it has become more stubborn to trigger with time, every new load can cause it to become more reactive. This is the ‘scary’ part of the situation as there are a lot of unknowns. 

What to keep in mind if skies clear enough for travel above treeline:
   1-  Around 2-3 feet under your feet or snowmachine sits a weak layer
   2-  The weak layer may or may not be reactive, this is the tricky part
   3-  If an avalanche is triggered in this deeper weak layer, it can be very large, propagate across the entire slope and fill the valley floor with debris
   4-  No obvious signs of instability are likely to be seen before a slope releases
   5-  Remotely triggering a slab from the ridge, sides or below is possible
   5-  Safe travel protocol and assessing the consequences if the slope slides, the larger the terrain the larger the potential avalanche

To complicate matters, other areas such as the Girdwood Valley have seen other weak layers  of facets associated with crusts. These are now roughly 2-3′ below the surface. All this said, it’s important to keep in mind that the snowpack harbors buried weak layers. 

Photo of the crown of the Widowmaker avalanche from Feb. 1st. It’s a bit tough to see, but the bed surface is covered in 1cm feathers of buried surface hoar that was the responsible weak layer.

Ridgetop winds associated with yesterday’s snowfall were moderate from the east. This is the perfect recipe for building wind slabs along ridgelines. Furthermore, a new batch of surface hoar grew last weekend and these slabs could be more touchy than expected if sitting on the surface hoar. Watch for cracking in the surface snow and stiffer snow over softer snow. Although wind slabs are likely to be shallow, they could be more dangerous if they were to step-down and trigger a large slab that breaks in the buried surface hoar discussed above. 

Loose snow sluffs:  Sluffs on steep slopes within the new snow should be expected.

Cornices:  We had a report of a large cornice fall in upper Seattle Creek drainage over the weekend. Heads up to give these an extra wide berth as they continue to grow. 

Glide cracks are opening again. We know of one glide avalanche that has released recently in the Summit zone just north of Manitoba. Heads up to look for glide cracks and limit exposure under them! 

Note the glide cracks in Seattle Creek’s Main Bowl (1st Bowl) on the slopes near the top of the photo. This photo was taken on Feb. 2nd, near the trigger point of the very large Widowmaker avalanche, which occurred Friday, Feb. 1st.