Snow-holing in Scotland has a long established history in both our own winter mountains and further afield. Over the last 10 years, snow-holing has grabbed the attention of the media and the viewing public. This exposure has introduced and encouraged people happy enough to pay for the experience. Andy Bateman* of Scot Mountain Holidays asks, should we assume what works in other mountains will work well in our own?
Likely Ambient Temperature
With the seasonal minimum in some recent Scottish winters approaching -20oC and an official record of –27.3oC, you would be forgiven for assuming you’d might be sleeping in temperatures approaching those of Arctic Norway.
Yet Cairngorm (1245m) has only ever recorded around half of this at –16.5oC (12th Jan 1987). Supporting this, Coire Cais Ski Base Station (630m) has a low of -9.2oC. The residents of nearby Nethybridge (210m) though, claimed the mercury dropped to -31.3oC on 10th January 1982. Satellite evidence suggests they were right!
The vital bit of information on these -30-ish lows are that they were all recorded during temperature inversions. The cold air flowed off the mountains and pooled in the valley bottoms where it cooled further whilst the mountain summits remained appreciably warmer. These record minima are in no way a reflection of the likely temperature you would find on our mountains. It’s not surprising when we’re never that far from a relatively warm sea in the UK!
So what temperature is likely when snow-holing in Scotland, let’s say, in the Cairngorms at around 1100m? The seasonal minimum for 900 m is usually around -8oC. At 1100 m this could translate to -10oC. Far more frequently winter temperatures at this height are around -5 and above. Our mountains simply don’t experience anything like the temperatures you might get in e.g. Arctic Norway.
Considering the warmer temperatures when snow-holing in Scotland, do we really need snow-hole features designed to capture warm air? Are sleeping platforms and cold air drains really necessary or should our aim be to lose the warm air?
Snow is a great insulator. A meter thickness in your roof and front wall is of vital importance in this regard. That is 20 cm of insulating snow both on the exterior and interior surfaces with 60 cm of well insulated structurally sound snow. Light penetrates to a depth of around 75 cm so if you see daylight, they’re getting too thin. It should also be borne in mind that a 1 m thick roof represents a considerable weight. It’s vital the front wall is adequately thick and strong enough to support the roof.
How high is that roof? Look at the apex centre.
Snow-hole sites by virtue of their high snow accumulation and steep slopes can be prone to avalanches. To be safe, you may need to pick a slope with a more gentle gradient and spend more time digging out the entrance. The majority of avalanches occur on slopes at or above 30 degrees. To maintain a 1 m thick roof, on a slope less than this, you’ll have to dig in a minimum 2+ horizontal meters from the top of the doorway before you start widening out the living area.
Avoid large areas of unsupported roof by keeping your snow-hole narrow. Aim for a depth of 2 body widths between the internal surfaces of the front and back walls.
This means you can create a relatively steep-angled apex ceiling which helps to avoid any drip points. Warm air can then be channelled towards the ventilation holes at the apex high points. In addition with it running the length of the snow-hole it increases the height with minimal snow removal giving everyone the opportunity to straighten their weary backs!
Importantly it also removes the unsupported dead weight from the ceiling. This is one of the most important aspects of snow-holing in Scotland. Although not mutually exclusive, removing the ceiling dead weight is of more importance to ceiling stability than temperature! Very few, experienced and inexperience alike, pay attention to removing the dead weight. I’ve managed to snow-hole once at +5 Deg C without any roof deformation! The roof of a snow-hole I constructed for the BBC Travel Show lasted through until around the 25th June!! The ceiling at that point was only a foot off the floor, but it hadn’t collapsed!! Every other snow-hole at that point was merely a hollow in the snow. As you create the apex be careful not to make the roof too thin. The strength of the roof is in it’s thickness.
Make sure there is good ventilation. My test is to regularly watch my breath. If it drifts off to one side it’s a good indication that ventilation is adequate. Cooking with pressure stoves in a poorly ventilated snow-hole is extremely dangerous due to the formation of toxic Carbon Monoxide. All pressure stoves work by first oxidising the fuel to Carbon Monoxide (CO) and then to Carbon Dioxide (CO2). The different colours in the flame indicate this. Irrespective of good ventilation a pan of icy water can have a severe quenching effect on the flame preventing combustion of the CO. Research for the British Antarctic Survey (BAS)** showed in heating a pan of icy water CO production could be significantly reduced by raising the pan supports higher above the flame. Snow-holers should acquaint themselves with the symptoms of CO poisoning.
To put this into perspective, I’m unaware of anyone in the last 25 years dying from CO poisoning whilst snow-holing in Scotland. I do know though, instructors who’ve attributed head aches to possible CO poisoning. It’s worth considering taking a small portable CO detector with you. In a snow-hole with a single entrance and no through air movement, ventilation may well be inadequate. Extinguish candles before you go to sleep as they also produce small amounts of CO.
Although the temperature may remain around 0oC you may well still be “injecting” appreciable heat energy into the snow pack. It takes considerable heat energy to turn snow at 0oC into water at 0oC so it will not be reflected in a temperature rise. It’s far more desirable that this heat energy drifts out of the doorways than being absorbed by the snow pack.
Make it large enough to stand up in. Large communal snow-holes are less prone to an abrupt temperature rise as they have better ventilation characteristics by virtue of having several entrances, etc. An entrance walled up with blocks in combination with an open doorway will often still allow plenty of ventilation.
Putting aside the dangerous scenario of cooking in a poorly ventilated snow-hole, I’ve never got up in the middle of the night to purely unblock a doorway for ventilation reasons. All the medical research I have seen (references below) doesn’t suggest there is any potential of becoming severely hypoxic in your sleep. Studies suggest sleep will become agitated, you will awake and in doing so get up and ventilate a stuffy snow-hole.
One potential hazard of digging a small snow-hole is you don’t have enough space to put the snow as you attempt to extricate yourself after a night of severe drifting. On one occasion I did have to tunnel out 1 ½ m before I hit the surface!
When it comes Scottish snow conditions, don’t underestimate how hard the snow can get. You will need a snow shovel with a metal scoop and a good snow saw. The sintering effects of strong sunlight and hard frosts of high pressure can make wind-slab snow astonishingly hard to dig. A good snow saw is often the only effective way to deal with this type of snow.
Many of the snow-hole sites are immediately adjacent to water courses. In addition, the snow pack often lasts well into the summer meaning there’s little opportunity for biological breakdown of human waste. If you do have to go you should do your business well away from the snow-hole site and far more preferably have some system to carry it out. Cairngorm Mountain’s Snow White Project has greatly improved the situation at the Cairngorm sites. All snow-holers coming to the Cairngorms are encouraged to use it.
The safety of a snow-holing in Scotland is often a reflected by the time it has taken to dig. I’m cautious about suggesting how long digging should take as it depends on a number of factors, not least the condition of the snow. From a “duty of care” perspective I feel a large communal snow-hole is much better than several separate small ones. I normally anticipate spending 4 to 5 hrs digging a 4 plus person snow-hole. I accept in soft snow conditions that this can possibly be shorter for a fit party of 2 each digging their own entrance.
With the vagaries of the winter weather, if done correctly Snow-holing is often the far safer option compared to a tented high camp in Scotland’s Winter Mountains.
* Andy holds the WML and IML awards and has over 20 years Mountain Leading experience. He has guided well over 30 commercial snow-holing trips in this time and although none of the mountaineering qualifications have a remit that covers snow-holing, he is one of the few guides deemed competent by HSE criteria of “relevant experience” to run snow-holing trips.
** British Antartic Survey helped in a BSc thesis. Available on request from andrew@scotmountainholidays.com
Medical references:
www.ncbi.nim.ni.gov/pubmed/18665947
www.ncbi.nim.ni.gov/pubmed/9340627
www.ncbi.nim.ni.gov/pubmed/8355417
www.ncbi.nim.ni.gov/pubmed/15265339
Andy Bateman of Scot Mountain Holidays leads at least 3 commercial snow hole expeditions in the Cairngorms Mountains every winter season. He has introduced scores of people to the magic of the winter season. He is also an expert at the skill of building a snow hole for a drip free night out in the mountains. To see what snowholing expedition experience is like for the customer check out our video on YouTube:
Seasonal temperatures on the high hills in Scotland are never as low as those in the valleys. You need to take this into consideration when planning to snowhole. Here in Boat of Garten we get temperatures of around -20oC. The lowest ever recorded temperature on the summit of Cairngorm is -16.5oC. Cold temperatures in the valley always occur under cold settled conditions. This is when the cold air drains off the mountain. The cold air then pools in the bottom of the valley. This means that in the Cairngorms the temperatures are never as low as in Norway.
In Norway, you need to capture the warm air. Most people learn to build snow caves in Norway. They learn to create features which capture the warm air inside the shelter. In Scotland, however, you are operating much close to the melting temperature of snow so sloping entrances, sleeping platforms and cold air drains become much less important for the snow hole expedition.
Roof sag is a combination of the temperature rising too much, poor ventilation and not having a thick enough roof or having a large area of unsupported roof. A roof and front wall of approx. 1m thick is vital. If daylight can be seen through either the roof or the wall, they are probably too thin. However, bear in mind that a roof that thick will need an adequately thick & strong front wall.
Avoid large areas of unsupported roof by keeping your snow hole more like a tunnel, narrow. Aim for a distance of no more than 2 body widths, side by side lengthwise. This means you can create a steep-angled apex ceiling which helps to avoid any drip points and allows you to channel warm air towards ventilation holes.
Many snowhole sites by virtue of their high snow accumulation and steep slopes are prone to avalanches. To be safe, you may need to pick a slope with a more gentle gradient and spend more time digging into the slope. To maintain a 1m thick roof on a 30 degree slope you will have to dig horizontally 2m from the top of the doorway before widening out.
Make sure there is good ventilation and regularly watch your breath then you will avoid carbon monoxide poisoning. If you see it drifting off to one side, it’s a good indication that ventilation is adequate. Never cook in a snowhole without regularly checking there is adequate ventilation.
It’s a good idea to create ventilation holes in your snow hole because of the Scottish climatic conditions.
Make your snow hole large enough to stand up in so you don’t get back ache from crouching.
One potential hazard of digging a small snow hole is that you don’t have enough space to put the snow when you attempt to extricate yourself in the morning. One of the snowholes Andy built in the Cairngorms involved digging out through 1.5m of fresh, drifted snow to get out in the morning.
Never underestimate how hard the Scottish snow pack could be. At least make sure your snow shovel has a metal scoop and that you are also carrying a snow saw.
Time taken to construct your snow hole is vital. A communal snow hole can take 4 – 5 hours to dig to make sure that you have the best construction possible.
See more about our snow hole expedition!
(A synopsis in pictures)
The snow’s back here in the Cairngorms and it’s only 4th November 2014 – plenty of time for the snow to build up for a fabulous Christmas and New Year in the Highlands. Take a look at our selection of winter images below – all taken in during winter seasons in the Cairngorms. Will it be an official white Christmas or just white on the high peaks of the Cairngorms
Photo caption: A day out in the snow – heading home in the sunset,
turning the snow pink and giving life to the Cairngorms –
also known as Mhonaidh Ruaidh (the red hills).
Photo caption: Sometimes a wee bit of cloud can play into your hands
and produce a much more stunning picture than a clear blue sky,
especially in the soft winter light we get here in the Cairngorms,
which is of course enhanced by reflection on the snow.
Photo caption: Unique to the Cairngorms National Park,
Britain’s only reindeer herd, which are free-roaming
across the hills in the winter. You could bump into them
on any of our courses or winter walking holidays.
Photo caption: White Christmas? Wouldn’t that be amazing?
This is the kind of snow laden scene
we’d all like to see, but how many of you would like to
experience it yourselves? When the snow lay round about,
deep and crisp and even …
Photo caption: It’s New Year and it’s Scotland – must mean it’s time for a party –
or as you’re in Scotland let’s give it the proper name and join the ceilidh!
Photo caption: Winter walking holiday across the Cairngorm plateau. Check out the blue skies!
Inspired? Check out some of our winter offerings in the Cairngorms and further afield across the Highlands of Scotland
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