Full depth? (Suit you,sir!)
17th March 2009
Full-depth avalanches of the type shown in the pictures are relatively common at ‘Meggie during sustained thaw conditions. They tend to be on the small side and occur in the same or similar places each year. The bed surface is almost always rock slabs or very steeply inclined grass which gets lubricated with water underneath the snow during a thaw. Glide cracks open up in the snow all the way to the ground and the slab of snow that is isolated has to overcome the friction offered by the rock or grass bedsurface. Meltwater assists this process but ground roughness can vary dramatically and so these type of avalanches are notoriously difficult to predict. In some respects they are a little like collapsing cornices and, it could be argued, are outside our remit.
The Great Slab of Coire an Lochain in the ‘Gorms is the biggest and best known site of large full depth avalanches where crownwalls 8m high are not unknown. The small scale events on Sron a Ghoire could threaten those using the usual descent path and if they were unlucky trundle them downhill. The Moy Corrie is also known for these types of avalanches where they tend to run on grass similar to the one shown in the shot below, though larger.
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