Snow shelters, staying dry

11:48 a.m. on April 2, 2010 (EDT)
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Its a known fact that snow shelters are damp - I mean they are made from frozen water...

I have once built a snow coffin from snow blocks, but a Boy Scout thought it looked like a good place to sit and retie his boots and fell through. He screamed, it was funny, he thought he was falling into a crevice. So anyway I didn't sleep in it. Another time I was tenting and felt energetic so I spent an hour and a half digging a snow cave for the heck of it. On both of these occasions I did have the idea that I would sleep in the snow shelter but did not.

So here's a question to experienced snow shelter users, since I have never slept in one ( but they make a wonderful place to have breakfast or light a pipe when its windy out, and they are really quiet inside) . In my attempt to get into my sleeping bag, everything I tried led to snow getting inside the bag. How do you get into a sleeping bag in a snow shelter and not get snow inside the bag? And if you get snow under the bag, doesn't it melt from your body heat and soak into the bag? And finally, how do keep a down bag dry enough on an extended trip, like climbing Mt Denali, sleeping in snow caves?

Jim S

1:00 p.m. on April 2, 2010 (EDT)
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Strange! I have never had the problem of snow getting into the sleeping bag in any of the dozens of snow shelters I have built, whether they were snow caves, quinzhees, igloos, or any variations of trenches (the snow coffin is basically a trench shelter.

As for the melt problem, you should put a ground cloth under the bag plus your pad (whether an inflatable down-filled Stephenson like you have or a Blue Foam) for insulation from the snow. Or put the bag inside a bivy sack. The melt will pretty much refreeze instantly, so no moisture comes through.

The inside ceiling of the shelter should be dome shaped and smooth, both for strength and so the when you and your bud warm the inside up, any melt gets absorbed by the snow rather than dripping from any "stalagmites" (any downward pointing protrusions and irregularities).

The snow in the Sierra inside a snow shelter is typically right at 0C/32F. The air temperature can get up to 35F or so in a 5 or 6 person shelter. If you have proper ventilation, even running a stove inside the shelter doesn't get the temperature more than about 35F - you really want lots of ventilation, because of the CO and oxygen depletion. The snow "breathes" pretty well, except that body heat and heat from stoves, candles, and the like builds a a hard glaze on the inside that pretty well seals the walls - if you stay in a cave for more than a couple days, it is a good idea to scrape the inner surface to get rid of the glaze and let the snow continue "breathing". I usually leave the entry door completely open, though there was one storm in which Barb and I stacked our packs in the door to block the drifting snow from coming in (that's the one, Jim, where Steve S and his girlfriend had to be dug out, thanks to some poor judgment on his part in digging their shelter 100 meters away from the rest of the group on the wrong side of the slope with a poor entry configuration - took some searching to figure out where they were when they had not shown up by 11AM the next morning).

In Alaska in winter and at altitude on Denali and Antarctica, the snow is pretty solid and is at a temperature well below freezing. So any melt is instantly re-frozen, although the air temperature does get up to about 0C inside the shelter.

Your down bag gets no damper than it does in summer from your sweat. But, as with any winter camping, you should squeeze all that moist air out of the bag immediately on getting out of the bag in the morning. Otherwise that half liter or so of perspiration during the night will freeze in the bag and accumulate a pound a day in weight (like the Steiger North Pole expedition where their bags weighed something like 70 pounds by the time they got to the Pole).

6:05 p.m. on April 2, 2010 (EDT)
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That's not what I mean. Every time I brushed the roof of my snow coffin, snow fell on my sleeping bag, and if the bag was open, it fell inside. When I tried moving onto the ground cloth I tracked snow onto it with my boots. If I tried taking off my outer gear, I knocked snow onto my bag. I know how to get into my tent and leave the snow outside, but if the snow is inside how do you find the space to shake it off and create a snow less area for your bag?

Jim S

8:35 p.m. on April 2, 2010 (EDT)
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Dunno, Jim. I have never had that problem. The snow coffin, like most trench shelters is pretty small, so you don't have a lot of room to move around. That was long enough ago (probably about 15 years) that I don't remember the snow conditions. One thing about doing any snow shelter that involves blocks (you used a snow block gabled roof as I recall) is that you have to dgi down into the snow a bit to get to the more consolidated stuff. This makes the block cutting and handling easier and the blocks will be stronger. Blocks cut right at the surface tend to be somewhat crumbly, though it depends on the snow history.

When digging a snow cave or bolt hole, it is best to have a roof that is 18 inches or more in thickness, which puts you at least into the consolidated layers (except in a fresh powder drop. If you do a quinzhee, you pile up the snow dome, tromp on it to consolidate it, then give it an hour or so to consolidate and refreeze. If your roof blocks weren't solid enough, I guess I can see that they would shed snow when brushing against them. But I have dug bolt holes that were not much more than bivy sack size and didn't have a problem with having snow get knocked off the walls and into the sleeping bag.

Trenches including snow coffins (usually made with a tarp/snowshoe/ski roof rather than snow blocks) and bolt holes are really emergency shelters, to be built in 15-20 minutes, so are a lot tighter than other snow shelters.

1:56 a.m. on April 3, 2010 (EDT)
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Trenches and bolt holes should be emergency options only, in which case the least of your worries is a little snow in/on your bag.

All other shelters built should have sleeping platforms elevated above the floor, both to put you in the higher, warmer, part of the shelter, as well as preclude snow covered boots, etc from tossing snow onto your bedding. If you are brushing the ceiling over your bed, consider providing a higher ceiling if possible. Finish the shelter poking one four inch diameter hole through the high points of the ceiling for ever two campers. As bill mentioned smooth the interior, and lay a tarp under your bag and pad.

Use of bivy sacks in snow is debatable. Those who favor bivies claim moisture condenses near the exterior wall of exposed bags, freezing before it can vent out of the bag. Those against bivies claim bivies preclude air circulating around the bag, trapping moisture in and around the bag. I have never used a bivy, and find the best way to preserve loft is a WELL ventilated shelter.

One tip to help retain down loft is bringing along a black plastic trash can bag. During protracted breaks, such as lunch, retrieve your down bag, stuff it in the trash bag, placed on top a blue sleeping pad, and let solar energy heat it up. Squeeze out the air every fifteen minutes, and then re-stuff your bag when ready to get under way. This helps even on cloudy days.

Ed

1:39 p.m. on April 3, 2010 (EDT)
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I like the black plastic bag idea, Ed. I don't go out with the idea of spending the night in a snow shelter, but have practiced the making thereof, working through and thinking through problems and potential problems, etc. The idea of heating the bag with insolation in order to minimize water catchment is a nice one. Should work in any cold-weather situation with enough sun, I'd think.

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