My post yesterday that I shared wouldn't show up due to my retardedness with technology! So before folk start going off as I've seen in one comment, this is ski patrol at Glencoe setting this off on purpose so the public don't get caught. Throughout the day I set off 12 avalanches in areas that had already slid, certain areas were sliding 3 times throughout the day and this is in a ski area that gets lots of skier traffic, so please be careful if venturing into the backcountry it is touchy at the moment.
Posted by Richard Hazelby on Thursday, February 18, 2016
From Richard Hazelby: “My post yesterday that I shared wouldn’t show up due to my retardedness with technology! So before folk start going off as I’ve seen in one comment, this is ski patrol at Glencoe setting this off on purpose so the public don’t get caught. Throughout the day I set off 12 avalanches in areas that had already slid, certain areas were sliding 3 times throughout the day and this is in a ski area that gets lots of skier traffic, so please be careful if venturing into the backcountry it is touchy at the moment.”
What it shows is the ski patrol cutting the bond on the convexity of the slope. As his skis cut through it creates a fracture in the weak layer which then spreads rapidly across a whole section of slope, which then releases.
Now, this is on a slope less than the 30 degree angle, see how easy it goes? If it was in the prime slope angle for avalanche to occur and with less runout, I would think it would be a far far bigger slide.
Remember, this is what a shallow depth slab release looks like, remember the ski patroller is just above the convexity, If he did this lower down the slope I think you would see him side slipping in the slab avalanche too.
Remember, it only takes snow depth just above your boot top, to disrupt your balance and take you down the slope in an ever increasing avalanche depth.
This is why fracture propagation is a key thing to note in any Extended Column Test – ECT.
We have all probably been up slopes as winter mountaineers, where the snow pack send shooting cracks from the tip of your boot, or when the whole area around your boot suddenly breaks away, leaving your crampon points working to find that, hopefully, firm well bonded snow underneath. Well imagine if it didn’t just do that?? And that fracture spread in a split second across the slope your on…
The classic ECT test above is designed to be repeatable, measurable results across a benchmark set of tests. Basically if one tap from the wrist on that shovel causes the whole slab, or weak layer in it, to release across the whole of the test block, then that is fracture propagation. If however it only caused the immediate area under the shovel to release, then that shows a slightly different state of cohesion in the test snow pack. Conversely if it took a full 10 swings of your extended arm smacking down on that shovel, then you could say the snow pack was in a very stable state of cohesion.
Something we use on our winter skills courses is the Be Avalanche Aware information from the Scottish Avalanche Information Service