Cornices

Above: Large cornices above Centre Post on the Post Face in Coire Ardair

Above: General shot of the Post Face and approach to The Window

Large cornices loom over many NE to S aspects at the moment. Don't often see big ones over Centre Post but these are conspicuously large. Loud and ominous rumblings were heard emanating from the Inner Coire today, nothing seen but was probably more cornice trundling down.

Big snow on its way on Friday. Stability was questionable in many places on Thursday and will get a whole lot worse. The avalanches could be big and run out to some distance.

Gratuitous pretty picture

Above: Ice on Loch Laggan before sunset on Friday. Note the high cloud.

We've had quite a few days of hard frost down at valley level (the loch is at approx. 250m above sea level) but have had high air temperatures near summits, so classic temperature inversions. Even with these high temperatures (+ 9 or 10 degrees C. at 1000m on some days) the snowpack has refrozen at higher altitudes. The very clear skies have allowed heat from the snowpack (yes, heat) to escape to the atmosphere by long wave radiation, even though the air temperature has been quite high. So the surface layers of the snow have cooled to give hard or very firm underfoot conditions. During the day any snow that is directly warmed by the sun gets a little mushy while the shaded slopes stay hard despite high air temperatures.

The wierdest example of this aspect of atmospheric physics I experienced was seeing heat haze shimmering up from the snowpack with snow drifting around my feet and an air temperature of +7 degrees C. (Cairngorm in March 1998). Convection, conduction, radiation: heat and snow make quite a conundrum.

Well, with more cloud forecast (but staying dry and cool) those South facing slopes are likely to be a little firmer during the day.

Old cornice and avalanche debris

Above: Huge pile of old cornice and avalanche debris at the base of Easy Gully in Coire Ardair

The car park was full today and we met a fair few people on the hill. Most were out hillwalking and everyone was staying clear of the gullies.

Most gullies are chockful of old debris, much of it from cornices that fell down on Wednesday night and during Thursday. The Inner Coire, including the final slopes up to the Window, had debris everywhere. Some debris tips had a lot of rocks and soil entrained in them, so much so that from a distance it looks like debris from a landslide.

Quite a few folk seemed spooked by all this and said the avalanche hazard must be 'bad' even though they hadn't seen anything fall down. Snow stability isn't too bad at all (although cornices still remain a concern) but people's perception of it is heavily influenced by these big piles of chunky old snow. Estimating the age of avalanche and cornice debris is very difficult for most people simply because they're not able to look at this stuff all the time. (Most Guides and instructors do have have a good handle on this for reasons that are self evident). A year or two ago an individual - from Dunfermline, if I remember correctly - reported an avalanche to SAIS HQ he thought had happened on a Saturday but had actually occurred nearly a week beforehand. We were in the vicinity on the Saturday and had looked at the debris which was so hard you couldn't kick your crampons in to it.

The moral of the story is, please do report these occurrences as feedback is vital, but do think carefully about the timing of the event as it will really help us in or 'accounting' procedures. Also, do remember that cornice collapse is a separate hazard often, but not always, independent of the avalanche hazard.

Above: a shot looking up Easy Gully today. We did our snow pit above the avalanche fracture line which is visible on the left side of the gully in the top quarter of the photo.

Almost a blue sky day

Above: Sron a Ghoire on Wednesday.

Beautiful day at Meggie. There's been a lot of snow transport in stronger winds and new slab is very weakly stabilised. Deepest stuff is at gully heads and corrie rims. Shears popped out just as the snowpit was being dug and a couple more slid out with very little encouragement. New cornices look pretty horrible right now as well. Elsewhere, there's large expanses of crusty snow-ice that's been well scoured. Should see some avalanche action on Thursday as snow turns to rain.

Above: Looking up towards Sron a Ghoire

Good skiing today down to 500m. Beautiful descent from the col traversing high beneath the front face of the minor peak left of shot. (Eat your heart out, Sam & Oliver!)

Thursday's looking desperate weather-wise.

Cornices - Monday 21st Jan '08

(Above) There are a few of these bad boys around at the moment. This one is about the size of a car and there are many larger ones hanging over steep N through E to S aspects, corrie rims and gully tops in particular. With rain and mild temperatures forecasted for Tuesday many of the younger ones will collapse and put a high loading on the slopes below, many of which are laden with deep windslab.

Above: The Post Face today (Monday). Coire Ardair has been pretty quiet of late. Snow stability has been pretty poor as 4 climbers found out in Raeburn's Gully on Saturday; fortunately no injuries.

Weds 16/01/08. Post Face principal routes

Above: Centre Post

Above: Easy Gully showing the build up on Last Post (some way to go yet)

Above: Opening pitches of Staghorn Gully

Click on the pictures for more detail.

Thursday isn't looking so great with some snow coming in during the morning turning to sleet and rain as the freezing level rising to 1300m.

So you want some snow...?

Avalanche debris (top of picture) high on the SE-facing slopes of Coire Ardair

A lot of snow on the ground at 'Meggie at the moment. Some high ground was swept clear of snow in the last storm but there's a lot at lower levels and the bottom ends of some gullies have serious quantities.

Ski-touring is fine if all you want to do is skin up hill; descents are nightmarish in bottomless stuff with a gnarly breakable crust in many places. Avalanche Man 'Cube' reckons snow shoes are the perfect tool for moving around the mountains at the moment (he was post-holing in his plastic mountaineering boots today so he would say that). The track right up to the lochan in Coire Ardair is incomplete and requires several groups of public spirited trail-breakers to make it passable. Where are Plas y Brenin groups when you need them?

Slab and loose snow avalanches overnight and today on SE to S slopes triggered by a temperature spike and warmth from the sun respectively.