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 Kootenay Bud
2695 Posts |
Posted - 03/02/2004 : 7:27 PM
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We were out skiing today on NE aspect slopes near Nelson and managed to trigger a 40 cm soft slab avalanche. We were actually mostly skiing trees, but the top of our first run had an open area about 40 feet wide. My partner ski cut the slope and as our dog took off after him, immediately triggered a 40 cm slab. My partner got off to the side quickly but our poor dog was caught and carried down. He kept moving his legs, which may have helped, as he ended up on top of the debris after riding it for a ways. We measured the slope angle at 40 degrees and the sliding layer was clearly surface hoar. At the walls of the slide path, it was very easy to see the slab sitting up on the surface hoar. Unfortunately, today was the one day I left the camera behind.
What I learnt: There is such a thing as negative conditioning. This was my third day out touring since the end of the snowfall on Friday and I hadn't seen anything move in the previous two days. We got widespread whumphing on Sunday but no evidence of slabs on 35 degree slopes and I was skiing 45 degree chutes on Monday with only surface sluffing. So, I was getting complacent.
And, it's the small terrain features that catch you. Further along the ridge where we were skiing there is a large open bowl (same aspect, about 34 degrees) which we were avoiding, but here we got caught on a small open area that I didn't look twice at. |
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 Super botonist, hippie chick who cuddles thistles with glee
Langley, BC
Canada
1541 Posts |
Posted - 03/02/2004 : 7:31 PM
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| Whew! Glad to hear your pooch was okay. |
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double-double seeking, snow-chasing, short-cutting, vertical feet collector
4523 Posts |
Posted - 03/03/2004 : 06:37 AM
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goodness, sandy! Good to hear that you, your partner and your dog are ok
how wide was the slab, and how far down did it go? |
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Kootenay Bud
2695 Posts |
Posted - 03/03/2004 : 1:56 PM
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Not wide at all, about 12 metres and ran about the same. Luckily, the terrain below was treed and the snow began to pile up and stop running. I have noticed that these soft slabs run much slower than hard slabs. I've been caught in a hard slab and that avalanche travelled about 200 metres in about 3 seconds - no time to react at all. What blew us away was when we measured the slope angle and found it to be 40 degrees. I had guessed about 32! Which means I am consistently underestimating slope angle by almost 10 degrees.
But, I really found that negative conditioning was a factor for me. You keep going out and judging snow conditions correctly - not getting caught, not triggering anything - and you start to think that you can read the terrain correctly all the time and the margin of error you would normally apply gets smaller and smaller, until there is none left at all. Then, whammy you get caught. |
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Surrey, BC
Canada
405 Posts |
Posted - 03/03/2004 : 3:50 PM
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| Sandy, what time of day? |
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Kootenay Bud
2695 Posts |
Posted - 03/03/2004 : 5:10 PM
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About noon. It wasn't related to daytime warming. It was a dry slab sliding on a northern aspect slope on preserved surface hoar. At the staunchwall of the slab you could actually see the slab sitting on the cross-hatched surface hoar. The exact phenonmena was pretty well predicted by the CAA, the bulletin for the region said:
Snowpack: Up to 15 cm of new snow arrived over the past 3 days and warm temperatures continue to settle the upper snowpack into a cohesive soft slab. The new snow lies on two prominent surface hoar layers, now buried up to 50-70 cm deep. These layers continue to release avalanches with human triggers. The easy stability test results reported by snow professionals throughout the region confirm this danger.
Avalanche Activity: Close calls continue in various parts of the Kootenays. A surface hoar layer down 40-50 cm in Kootenay Pass surprised two different groups Sunday, fortunately only a little gear was lost. Elsewhere in the region, accidental and controlled avalanches released on the two surface hoar layers within 40 cm of the surface, primarily in treeline and low alpine elevations.
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Surrey, BC
Canada
405 Posts |
Posted - 03/04/2004 : 5:41 PM
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| Thanks for your report & findings. It is a kick in one's complacency; and a kick in a negative feedback loop. |
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Dog takes a ride in slab avalanche
