Advising the use of a snow cave without the caveats
From BearWiki
Claim: Snow caves make poor, potentially dangerous shelters, and should only be used as a last resort.
Bear described spending a night in the snow cave as the worst night of his life.[1] If not done right, a snow cave has the potential to be the last night of a person's life as well.
Snow shelters have the following properties:
- A temperature of "around" zero degrees centigrade. Rise in temperature above this encourages melt, exposing fresh snow.
- A wall temperature of "around" zero degrees, for the same reason. All objects emit infrared and receive it from the objects around them; this is why standing near a fire makes your skin feel warm even when the air is cold. Infrared is the most significant heat loss mechanism when temperatures are low (and thus evaporation from the skin is insignificant)
- Vulnerability to collapse, especially if the temperatures outside are proportionally warm.
The last case is a particularly nasty one. A collapsed snow tunnel is like being buried under an avalanche. The deeper the shelter, the more severe your problems (inability to dig out, lack of oxygen, etc) if it collapses. A ceiling thickness of about 12" is optimal as far as safety is concerned.
Sometimes, digging a tunnel in the snow is your only option to escape from biting winds. In such a case, it is better than nothing. Make sure that it is no bigger than is needed, and that the entrance to the tunnel is lower than you are (to keep hot air trapped in, as it rises). The roof and walls should be smoothly sloped to channel melt away. However other shelters are much better: caves and cliff overhangs, natural pits under fallen trees, lean-tos, and so on. If there is any wood at all, a greatly improved snow shelter can be made by finding a depression in the snow, placing branches over it in a dome, and piling boughs and plant debris (or snow, if unavailable) atop them for insulation. This provides for a stable roof, provides extra insulation, and shields you from the ice on one side.
[edit] Analysis
Support: This is another alpine area where bear gets some terms correct, but absolutely blows the application. He may be a good rock climber, but he's not an experienced alpinist. In the Alps episode, he makes a shelf in the snow, not a snow cave. Even cheating and using his parachute as bedding for his sleep, I doubt he could have spent the night there without MAJOR frostbite. Having a depression in the snow for a cold sink is irrelevant since he's on a snow shelf, not in a snow CAVE. A snow CAVE can actually be a relatively warm affair, and can be around 32 F inside even if external temps are far lower. Digging a small hole in the cave is not a real cold sink; you either need to have an elevated sleeping platform OR tunnel up when digging out a snow cave for this to be effective. Some references for snow caves follow.[4][5][6]
Support: It's also worth noting the deception told by Bear in the same episode: he says it snowed that night he stayed in his shelter, but when he popped through the roof of his shelter, it was old snow that had gone through at least a few freeze/thaw cycles, and the surrounding area had no accumulation of new snow, including the nearby rocks that appeared exactly the same as they did the day before (assuming the scene was actually shot on a different day).
Oppose: What? Humid air feels colder? I come from the land of the ice and snow, and humid winter air is very pleasant and warm. Unfortunately when you're below freezing the humidity all disappears and air becomes bone dry, since moisture crystallizes out of the air. The whole assertion makes no sense.
- Support: Water is a far better conductor than air which, in fact, is a great insulator. The more water floating all around you (humidity) the faster the heat exchange. What you're experiencing with the humid and hot winds is just one of the many features of your local climate which has nothing to do with the topic.
