2nd January 2021
(Above) The reverse view of the first photo. Looking down to Loch Laggan from the broad NE shoulder of Sron a Ghoire. Wintry today. Had a few rogue snow showers in the early hours (about an hours worth of light snowfall in total) carried on N winds. Lightly scoured areas on windward slopes – like in the foreground – but with new weakly stabilised windslab building in lee areas.
(Above) New windslab formed over a very thin crust-like feature at the top of the snowpack. Instability was pretty obvious in this new snow. The shallow block of snow released very easily when isolated with a top cut. Read on…
(Above) 12.50hrs. Small dry slab avalanche test triggered on a SE facing steepening at 720m in the lee of the wind just 30m away from where the previous photo was taken. Longish crownwall (circa 80m and top left of shot) but only 15cm deep and running out 10m or so. A low consequence event for an unprepared walker/skier in this location but different where the run out is much steeper/longer perhaps over rocks or a crag when the outcomes could be much more serious.
(Above) What’s ‘test triggering’, you may ask? In simple terms it’s the ‘controlled’ release of a minor avalanche prone slope. Avalanche techs worldwide carry out innumerable ‘ski cuts’, that is, skiing aggressively from point of safety to point of safety over a short distance at the very top of a slope – quite often protected by a rope – to see if they can trigger it. As a forecaster, triggering an avalanche dispels your uncertainty about stability: it’s unstable! There were all sorts of clues this minor slope would slide as documented above. Now look at the top left of the photo and you’ll notice where I made a fair old mess of the new snow surface by jumping around on it to see if it was reactive. You can also see where I got the slabby snow to just crack – in this case a sort of pre-release – and snow cracking like this is never a good sign and often mentioned in all SAIS area blogs. Having got the snow to initiate some minor degree of shear-fracture I moved forward down the slope a little, repeated the exercise and was rewarded with the hiss of snow as it slid en masse away from me.
Test triggering a slope is not for the uninitiated and we do not recommend it.
In certain circumstances, such as today, when the runout is very short and smooth and the slab build up modest it becomes a legitimate tool to deploy from our avalanche diagnostic toolbox but it’s not something we do very often.
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