Discussion in the Storm Doris thread - thanks Dave K for asking the question - got me thinking that it would be good to share stories of avalanche-related decision-making mistakes. If we can learn not only from our own errors but from others' too, we'll hopefully not have to repeat them.
My story concerns descent from a climb on Mess of Pottage a couple of weeks ago.
The wind, if I remember rightly, had, unusually, been easterly and it had been strong, with some snow on it, so we knew there would be quite a bit of unstable windslab about, so our original thought had been to climb with bags and walk off. But then, as we approached, that west-facing slope back down to the corrie from the col north of MoP (often referred to as Windy Col) looked less steep than I remembered, i.e. under 25 degrees. We knew it would be windslabbed, but at that angle it wouldn't matter. What we should have done was get the phone map out and calculate the slope angle (which turns out to be 32-odd degrees, i.e. prime windslab avalanche terrain...) but, with other teams about - it was a Sunday - we wanted to bash on and get on the route, given that the shared first belay - at the bottom of The Message - is probably the most overcrowded in Scotland! Even as it was, we had to queue behind one team. The prospect of climbing bag free, avoiding what would be an extremely windy descent that day from 1141, and not needing to hold everything up by faffing with the map and calculations was very attractive, so we let ourselves be lazy and optimistic. Salutary. We were lucky to get away with it.
(For those that don't know, the way to calculate slope aspect is to find the steepest bit of the slope and divide the height lost by the horizontal distance, then get the inverse tan of that number. Handily, the inverse tan of 0.5 is 26.5 degrees, i.e. if height lost is less than 50m per 100m horizontal, it would be take pretty exceptional conditions for such a slope to avalanche. Phone maps are great for precise measurement of distance. Obviously all this is best done in advance of the climb, as, like us, you won't want to be faffing with this once it's cold, you're wearing gloves and you're trying to get on a route.)
So, lessons learned: think properly about various descent options in advance of the day. If you consider changing plans during the day to something you haven't properly planned for, force yourself to do the work. It's like abseiling in a blizzard when it's dark: force yourself to double check everything. Be wary of believing what you want to believe for the sake of comfort and convenience. It's easy to talk each other into this as a pair, particularly when you're with someone whose judgement you trust.
Edit: a potentially useful tool in the field is a clinometer app for your phone. Some compasses come with them built in. Also worth stating that, although I had both on the day in question, I failed to use them, even though I thought of it as we became worried in descent. It was because, at that stage - at dusk, very windy, tired and a bit cold, and in the knowledge that there was no other safe descent back to the bags that didn't involve a long detour - we both really badly wanted to believe that what we were doing was OK, plus faffing with the phone/compass felt like too much effort. Having said that, I think it might have been different if there'd been a terrain trap rather than a snow field at the bottom - fear outweighing laziness. But it remains that, had one or both of us been avalanched, the consequences could well have been serious.
Post edited at 19:00
