The Awkwardness of an Easterly.

10th February 2024

Although not quite as cold as previous few days, snowfall through the morning made it feel nice and wintry on Aonach Mor today.  The old snowpack which got a drenching at the start of the week is now (unsurprisingly) bullet hard. There are also various patches of water-ice about. These tend to be smaller in extent, often small enough to be completely covered by the fresh snow. This resulted in a few slips and falls on the walk in and out.

The wind was from the East, and this wind direction can be a tricky one for writing the avalanche forecast . Normally the greatest avalanche hazard is on the lee side of the mountains, if there is a South-Westerly wind with snow for example, the greatest hazard tends to be on North to East aspects. Simple! However, with an Easterly things can be a bit more subtle, particularly when the snowpack is as it is at the moment. This is due in part to the shape of the mountains, and the distribution of the existing snowpack. There is (or until last night was) very little snow  on Westerly aspects, and that means that the fresh deposits on these aspects tends to be sitting on bare often bouldery ground which improves stability. Also the bowl shape coires that often face North and East cause the winds to swirl round and deposit windslab, often below the crags, on windward facing coires. The distribution of the old snowpack, means that any fresh deposits are often sitting on uniform hard icy surface of the old snowpack.

It is easy to get caught out by these patches of windslab. That nearly happened today, a pair of friends of mine were walking in to Coire an Lochan to go climbing. They were cutting across a North or North-Easterly aspects in Coire Dubh just before climbers col, and triggered an avalanche in a pocket of windslab. Fortunately they were able to step off it and continue (paying a bit more attention to the snowpack) to have a good day’s climbing. However, in the current conditions it would not take much in terms of an avalanche to knock you off your feet, and the results of that could be very serious. On the other hand, the patches of slab are not extensive, and in a lot of places it is easy to approach routes avoiding the these patches altogether.

Soft snow on a firm base! The fresh snow was hiding patches of water ice. In some places such as in this photo it was quite obvious, in other places they are not so obvious, something resulted in me ending up on the ground more than once.

On the crags of Aonach Mor the turf is well frozen, the old snow-ice is really really firm, and I heard reports of really good snow-ice in some of the gullies. No having to worry about whether Schrödinger’s Turf will be frozen, not frozen, or some other superposition of the frozen/not frozen wave function.

Lots of climbers out gearing up at the summit hut. This is the busiest I have seen the summit hut are in terms of climbers for a few years now.

The top of Easy Gully was scoured down to the old hard neve, and thus totally stable. The tops of the gullies on the Coire an Lochan tended to catch the wind and be scoured. 

The view over the the crag to the South of Easy Gully in Coire an Lochan. Unfortunately the light was a bit flat, so hard to make out in the picture, but pockets of windslab could be seen below the crags from this location.  

Looking along the top of the crag. In the foreground partial erosion of the soft surface layers of the snowpack can be seen on the flat area above the cornice. 

The crown wall of the triggered avalanche on a NE aspect at an altitude of about 1050 metres today. Contrast was not great, so I have tweaked the image so that the crown wall shows up better. I was caused by the failure of  part of a large pocket of windslab sitting on top of the hard neve. The crown wall is not deep, maybe 25cm or so, but enough to potentially take you off your feet which, with the current bullet hard neve, could well be very serious.

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