Microwave Tower North Slope

Activity

Skiing

Total in the group?

4

People partly buried with normal breathing?

2

People not injured (caught but not buried)?

2

People involved?

4

Terrain shape at trigger point

Convex

Snow depth at trigger point

Shallow

We ascended up a ridge (bottom right of first photo) and then turned east (left from photo POV) across a low angle bench sandwiched between two steeper slopes. Before traversing the bench we contemplated the upper slope and it seemed to not be too steep, maybe 20 degrees from what we could see at the time. This was wrong, as it was more steep than it appeared and only seemed so because of the poor visibility. We were traversing the bench to get to another ridge to take us to the top and as I reached the first rocks of the ridge we remotely triggered a wind slab. It propagated from the rocks 100 meters uphill to the top of the slope, then 300 meters along the top of the slope to the West, and then another 100 meters along the east facing slopes. In some areas the crown was over a meter deep. The force of the slide also triggered slides in the slopes that were below us out of sight. Second photo has red lines showing the different crowns and how it propagated to other slopes.

We were lucky, as due to the low angle of terrain, the slide above us never made it into the tracking phase. However, we were all caught in the slide. Two of us were pushed back a meter or so by the huge slabs (third photo) and two other party members were partially buried, with one needing to be dug out by the other. If we would have been on steeper terrain, we would have been taken to the bottom.

Signs that we had seen throughout the day were:

1. Shooting cracks going 50cm away from our skis as we ascended the FSR, on wind affected snow

2. A whumph heard by one of our party on our first lap down

As we skied down, we passed over the slide and debris of the lower avalanches. The layer that the slide occurred on was shallow and crusty. We suspect this may be the surface hoar layer that formed about a week ago in lee terrain.