Come autumn, the hills in Scotland look as empty of snow as anywhere else in Great Britain. And yet, there are some special places hidden from view where winter stubbornly hangs on despite the passage of summer. And, quite unexpectedly, the snow that falls in those places only rarely melts.
These long-lasting ghosts of winter, which vary in size from mere pin pricks to enormous things the size and volume of buses, are Scotland’s famous snow patches.
They’re a source of fascination and curiosity for most folk who wander the hills during the warmer months, and I’m no exception. I’ll always go and take a closer look if I spot one because they take on the most wonderfully weird and wonderful forms as they melt.
Until last month the latest I’d stood on old snow in a given year was August, in the Cairngorms. However, if I’d been more adventurous and had actively sought snow out, I could have done so later than that in every year since 2007, and in most years before that. 2006 was the last time there was no snow at all in Scotland.
But while I’m not that die-hard a chionophile (yep, snow lovers even have their own name, derived from chioni, the Greek word for snow), others most definitely are.
Iain Cameron is a self-confessed chionophile whose interest in snow patches sees him clambering under crags and up gullies in all weathers, visiting the kinds of places most hardened hillwalkers will never see let alone visit. Consequently, outwith the winter months Iain and a few others like him are probably more familiar with snow and its whereabouts than anyone else in Scotland. They keep an eye on the dwindling number and sizes of patches and start paying them personal visits.
I accompanied Iain to Creag Meagaidh on 28th October on one such visit, to a steep slope at the top of Raeburn’s Gully, high above Coire Ardair. He had reliable information from the previous week that we would find old snow there, but after several days of torrential rain we feared the worst.
To my delight, the patch had survived. Furthermore as we got closer it became apparent that it was rather large. Using a laser ‘tape measure’, Iain recorded it as 28m x 20m at its widest points, and an impressive 2m deep.
Though I’d encountered snow patches before, it was quite something to see such an inaccessible and long-lasting one close up so late in the year. Iain showed me the different features of the snow patch, and explained how it was sculpted by wind and water.
It was a fascinating encounter. But while Iain’s visits feed his own personal fascination, the data he records also contributes to an impressive catalogue of observations dating back to the 1930s. Those of 84 year old Adam Watson, the celebrated ecologist, writer and environmentalist whose knowledge and familiarity with the Cairngorms is unrivalled.
Not a scientist by trade, Iain speaks with pride and fondness at the long tradition of ‘Citizen Science’ across the UK, and amateur snow patch surveying certainly qualifies as that.
The internet and, in more recent years social media, have brought the subject greater exposure and publicity, and Iain is now one of a small army of outdoors enthusiasts who seek out, log or photograph the snow patches they encounter.
The information they gather feeds into an annual paper on the number of patches that have survived until the first lasting snowfalls of winter, co-authored by Iain and Adam Watson, and published by the Royal Meteorological Society. The study offers a valuable insight into long term patterns of snow cover in Scotland’s hills.
Aside from their importance to us as scientific study, snow patches also have an ecological importance to upland wildlife.
Snow patch habitats are truly arctic environments where, for the majority or even the whole of the year, vegetation is completely covered. Because most flowering plants cannot grow under these conditions, species of mosses, lichens and liverworts gain a foothold they mightn’t otherwise have.
Other plants, which would quickly perish in very cold and exposed locations, get protection against frost damage or desiccation from the wind. This is because lying snow creates its own microclimate, affecting temperature and humidity at its surface and edges, and protecting and insulating the ground.
Provided it is greater than 15cm in depth, the bottom of the patch can maintain a relatively stable temperature of between 0C and 1C all year round. As there are very few locations where this happens, these habitats are extremely rare and precious.
When the snow patch starts melting it prompts a growth of grass on the newly exposed fringes. Snow buntings feed on insects and seeds around the melting edges, while the melt water creates wet flushes down-slope.
This not only creates localised bursts of alpine plant life, it is also a source of nourishment in times of drought. Not least for thirsty hillwalkers when the burns and springs are dry. But the patches also offer relief for upland creatures during hot weather, or provide a refuge away from biting insects. It’s not uncommon to see red deer or reindeer clinging to snow patches during the summer.
How and where do snow patches form?
When snow falls across the uplands it rarely does so in a gentle downward manner. More often than not it falls in violent storms that batter the summits for days and, like sand in a desert, snow is moved around by the wind even after it has reached the ground.
The snow is driven across, up or over a hillside or plateau until it reaches an obstacle that can collect it, or until it reaches somewhere less exposed and less turbulent where it can be allowed to settle.
Leeward (facing downwind) slopes, gullies, crags and coires are perfect for collecting snow and this is why, after a storm, one side of a hill can be almost completely scoured bare of snow, while its opposite side is a blemish-free white carpet.
The wind swings from one direction to another and snow is deposited on different slopes at different times. But for the most part our weather comes from the Atlantic. This is our prevailing wind direction, travelling from southwest to northeast. Over the course of the winter the majority of snow therefore accumulates on aspects that are sheltered from that prevailing wind, ie slopes, coires and cliffs that face between north and east.
But accumulation is only half the story. Next comes the melting, for which location is again key.
The rate of melting depends not only on temperature, but also wind, rain and sun. All three can hasten snow’s demise but warm rain borne on a mild wind is its absolute nemesis. And there’s certainly no shortage of that in Scotland.
Water finds its way down through the snow or runs underneath the snow pack, especially if it sits on bare rock. Warm winds also work away at the patch like a hairdryer. Snow that is directly exposed to the prevailing weather (ie on south or west facing slopes) offers little resistance and, generally speaking, patches on those aspects are among the first to go.
But snow that is hidden away, high up in north and east facing aspects is, for the most part, sheltered from the wind and rain. It is also sheltered from the sun, which strikes southerly aspects the hardest all year round, but which barely reaches the most sheltered northern aspects even in summer.
Unlike mountains in continental Europe where it can stay cold for long periods, the variability of Scotland’s maritime climate means a lot of our snow melts even during the course of the winter. But ironically it is this constant thawing and refreezing that contributes to the longevity of our snow patches.
When snow continually thaws and refreezes, the air trapped inside is released and the snow consolidates. It packs down. New snow on top is incorporated into the snow pack and it all compacts and gets harder. The harder it gets, the more like it ice it becomes, and the more difficult it is for wind and water to penetrate.
The beginnings of glaciers
If snow patches are beginning to look or sound like something approaching a glacier, then you’re absolutely right. It’s just they never get beyond that early stage in Scotland because there’s no net gain in snow year on year. If these dark recesses ended each year with more snow than the year before, then slowly but surely glaciers would form.
After all, these dark, remote places high up on our cliff faces and coires are the very places the glaciers gave up last, and are the places that glaciers would return to first if the climate cooled a tad.
And it is only a tad. It seems generally agreed that a reduction in average annual temperatures of around 2C would be enough for these places to make net gains in terms of snowfall. But that’s easier said than done.
Deviations of 2C from the average temperatures we experience aren’t unusual across one or two calendar months. In December 2010 Scotland as a whole was 5C cooler than normal, and some parts of the country were a staggering 7C cooler than usual! But such deviations are rarely sustained over more than a few months and, these days any deviation tends to be in the other direction, with warmer than average weather.
Still, it’s enticing to imagine us getting a run of cooler years and perhaps seeing winter take up permanent residence in our remote, cold and dark places.
How many snow patches this year?
At the time of writing, in early November 2014, the snow patch locations and number are as follows:
Most of the locations listed are the same ones that hold snow most years. Ben Nevis and its 4000ft neighbours, and the high coires of the Cairngorms.
In particular, Garbh Choire Mor on Braearich where the snow is more durable and long-lasting than anywhere else. The snow there has completely melted only five times since the 1930’s, and anecdotal evidence suggests it may have melted just five times since the 1700’s! Those confirmed melts were in 1933, 1959, 1996, 2003 and 2006.
The unusual additions this year are on Creag Meagaidh and Carn na Caim, the latter of which is a west-facing patch overlooking Dalwhinnie. According to Iain, the last time snow survived to the following winter on Creag Meagaidh was 1994, and 2014 looks set to be the first time snow has survived outside of the Nevis region or the Cairngorms since 2000. A result of the extraordinary conveyor belt of storms and above-average precipitation experienced at altitude last winter.
A big thank you to Iain Cameron for his guidance and assistance in writing this piece, and for a great day on the hill.