Drifting and scouring
6th February 2017
(Above) On the path in Coire Ardair. Dry today but windy and cold to start. There’s a fair amount of fresh snow lying around in many places and this was soon shifting around quite dramatically as the winds picked up through the morning.
(Above) The prominent SE ridge of Coire Chriochairein. Spindrift in volume being scoured off windward slopes but only localised deposition in the lee areas. A fair amount of of lee slope scouring on lower altitude slopes as strong counter winds developed after the prevailing South Easterly gale strengthened. Quite bright this morning too, though that didn’t last.
(Above) The backwall of Coire Chriochairein (the col on the skyline is at 970m). This slope is bang on South-facing and more or less devoid of snow after sustained wind scouring. The finer scree deposits in the centre of the shot are from a sizeable landslip here about 3 winters ago and mass movement terracettes are now clearly visible, no doubt enhanced by the movement of deer along them.
(Above) Deceptively tranquil-looking scene towards the end of the path, with Pinnacle Buttress, the Post Face and The Window prominent. The winds swirled around fairly dramatically at times in the base of the coire, see below:-
(Above) Looking West. Detailed shot of the Inner Coire of Coire Ardair. ‘The Window’ (the col in the centre of the shot) is normally approached via a sustained snowy slope at this time of year but right now is a scramble up scree and talus. Spindrift was seen to be swirling up the crags (in the lee of the prevailing wind) to the left of the picture: more evidence of the effect of strong counter winds in lee slope areas. However, windslab deposition was occurring at the very top of those Inner Coire crags and gullies.
(Above) Made it (just!) up into Coire nan Gamhna, a hanging glacial valley above the lochan in Coire Ardair. It’s a proper little amphitheatre with its very own small lochan in the bottom of it. The wind tends to swirl around features like this when wind speeds are above about 40mph, depositing and scouring snow in what seems to be a quite haphazard pattern. The top of the backwall (centre of photo) is at 970m and is an exact NW aspect. Spindrift was piling in over the top of the col but only a relatively small percentage of it landing to form windslab. Slab distribution at the top of this backwall is quite localised. Some of the gullies immediately East of Bellevue Buttress (N aspect) did however receive more windslab build up.
The photo above doesn’t quite capture the really wintry nature of conditions today but this video clip – shot in the coire and looking up to the summit of Puist Coire Ardair – certainly does:-
(Above) Windslab distribution was localised but stability definitely poor where there was build up. This shooting crack appeared in a small hollow as I approached from above. Quite a deep failure, too.
(Above) Noticeable cross-loading on a few East-facing aspects today. Quite easy to spot the cross-loaded windslab lying on the wind-sheltered left side of Centre Post’s exit ramps. Expanses of concrete-coloured snow-ice visible on the more wind-exposed right-hand side. (The Post Face is an exact East aspect).
More snow and wind in the forecast so instability expected to be more widespread on Tuesday.
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