The Sunburst Avalanche

Last Saturday, Chelsea and I decided we wanted to do an overnight tour, going up the valley between Sunburst and Magnum peaks. Talking about it at home this seemed like a good idea. Over the past week there had been about 7-8 feet of new snow in the Pass, and we knew the snowpack would need time to adjust to this new load; so it was a good time to cool our jets about the steeps and do more of a tour.

The primary avalanche concern for the area was a layer of buried surface hoar. This entails those beautiful, feathery or blade-like crystals of hoar frost that commonly grow in cold clear weather on the snow surface and are subsequently buried. This is the most common type of weak layer that is involved in fatal avalanches, because it does not give any of the classic signals of severe instability (whoomphing noises and shooting cracks). It was now underneath a 7-10 foot thick cohesive snow slab.

Once we started skinning through the valley, however, with our heavy overnight packs on, we began to doubt the seriousness of the snowpack instability. Skiers whooping down faces that we would have loved to be on was hard to watch.

The farther up the valley we got, though, the more I thought that we had made a poor choice of overnight snow caving spots. We was looking up at the steep slopes of Sunburst and Magnum hanging over our heads, and we grew increasingly uncomfortable.

Buried surface hoar, except in extreme cases, is resistant to remote triggering (i.e. you will not trigger a slope above/around you from a low angle slope nearby). So Chelsea and I had a quick conference and decided that we were ok with skiing underneath these slopes, as long as nobody was coming down them. No sooner had we decided this, then a group of skiers appeared 1500 feet above us and started trundling chunks of cornice down to see if the slope was stable. They rolled almost to our feet, and we quickly decided that this was a death trap (complete with a gully behind us to get washed into). We decided we could go snow caving somewhere out in the flats and have just as good of a time, so we ripped our skins and headed down.
The pictures below show what happened less then five minutes later, as the group of skiers headed down.

Milliseconds after fracture initiation. The skier jumped off the rock outcrop above him and most likely triggered the avalanche when he landed.

(photo by Peter Knape taken 2-23-08)

This avalanche was 1/2 mile wide with a crown face up to 10' deep. It ran 1500 feet to the valley floor and 200 feet up the other side, triggering a sympathetic release off Magnum.

(photo by Peter Knape taken 2-23-08)

Looking up from the debis pile. Notice the deep crown face as well as where it stepped down to deeper weak layers.
(photo by Lisa Portune taken 2-24-08)

The crown face (photo by Lisa Portune taken 2-26-08)

The search and rescue helicopter touches down on the debris pile. the skier that finally triggered it was the sixth one down the face. He was buried for 30-35 minutes, and was blue and unconsious when he was dug out. Another skier was knocked over and partially buried by the powder blast. Luckily, they were both wearing beacons, and no one was badly injured.