Perennial snow in the Scottish mountains
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Perennial snow is snow that falls in winter and lies throughout the summer without melting until the following winter's snowfalls. This new snow can lie on top of the unmelted old snow, and this is a condition for the formation of glaciers and icecaps. There are two main areas in the Scottish mountains where perennial snow exists; Lochaber and the Cairngorms. The extent of long-lasting snow varies enormously from year to year and decade to decade; as an example see the three photographs of Coire an t-Sneachda in the northern Cairngorms below, taken by myself over a range of 27 years but at the same time of year (late June/early July):
The summers of 1983 and 1994 saw an unusually large extent of perennial snow throughout the Scottish mountains. From about 1995 until 2006 there was a noticeable reduction in this long-lasting snow cover (with the exception of summer 2000), with some years having no snow surviving until the following winter at all (a surprisingly uncommon occurence in the previous decades). Some attribute this to rising global temperatures; see the resources below for detailed discussions of this. In the last few years however, this trend of declining perennial snow cover seems to have reversed somewhat. The winter of 2009/2010 had very large snowfalls and low temperatures and may well have had the greatest amount of snow cover and depth in the Scottish mountains since the winter of 1978/1979. However, this large winter snowfall has not contributed to an increase in the number and extent of snowpatches remaining in the mountains throughout 2010, as numerous factors apart from winter snowfall levels contribute to snowpatch survival, including the prevailing wind direction throughout the winter months (which was predominantly from the north and north-east in 2010) and air temperatures and precipitation levels throughout the spring months. I have not been to the long-lasting snowfields in Lochaber, but I have walked on the Cairn Gorm - Ben Macdui plateau many times (the first time being in 1983 when the photograph above was taken, when I was 12 years old), and this area contains the most easily accessible snowfields. Broadly speaking, there are 5 areas on the plateau that can usually be relied upon to hold long-lasting (although not necessarily 'perennial') snow in most years (click on the area name to get my archive of photos of that area):
Other areas that hold long-lasting snow, although perhaps less reliably, are the Cuidhe Crom (or 'crooked wreath') patch at the head of Coire Cas (near the ski slopes and visible widely from the Spey valley), the upper March Burn, upper Coire Mòr and upper Coire Clach nan Taillear (all on the western edge of the plateau above the Lairig Ghru). However, there is one other area in the Cairngorms that I have not been to yet, and which holds the distinction of having the largest extent of perennial snow in Scotland, and this is Garbh Choire Mòr, south of the summit of Braeriach. I do however have a strong memory of seeing old snow at the top of the cliffs of Garbh Choire Mòr on the way from Sgòr an Lochain Uaine to Braeriach in September 1994 and being amazed that there was still snow from the previous winter so late in the year. If glaciers were to ever start forming in Scotland again, this would be the first place they would appear. Resources I've written several postings on my blog about this topic and I have discovered a few websites and publications that I've used to explore it further, although it's still very much an unexplored and esoteric area, even amongst people who spend time in the Scottish mountains. Some resources are listed below and provide a good overview - the academic papers in particular are a mine of data and information if you can get access to them. The acknowledged authority in the study of long-lasting snow in the UK (as well as being an expert in the ecology of the Scottish upland environment, particularly the Cairngorm mountains) is Dr. Adam Watson. My blog postings:
Websites:
Books:
Academic papers (the full text of many of these papers are only available from academic libraries or online from subscribed institutions):
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