Monday, December 17, 2012

Wilderness Survival - Part 3.5: Snow Caves!

More on Shelter – Snow Caves 

Entire books could be written about natural shelters.  Rubbish huts, wigwams, rock shelters, lean-tos, dug outs, various log huts, thatched and grass shelters, snow caves, and on and on.  Many of these shelters take quite a lot of time to construct.  For long term living in the wilderness, these are great.  But for emergency shelters, one needs something that can be thrown together quickly in poor conditions.  These are the types of shelters we will focus on for our wilderness survival series.  Again, when it comes to survival, think small, dry, insulated and quick.

Since it is winter (or will be in four days), a discussion of snow caves seems timely.  Snow is a wonderful construction medium.  From it one can build shelters as simple as a hole in a drift through mound caves, a-frames, and igloos all the way to ice castles.  These shelters can be surprisingly warm.  But which of these work when time is limited, darkness is falling and a blizzard is moving in?  How can an overdue adventurer create a life-saving shelter in a minimum of time to get through a surprise night in the wilderness?  Most snow shelters take a lot of time to make and they are all dependent on snow conditions.

For winter adventures, one should plan to spend a minimum of a couple of hours building a snow shelter, and they often take longer than that.  But when time is minimal and shelter is critical, we need a faster solution.

Perhaps the fastest is a simple hole in a snow drift.  This solution may save your life, but it can be cramped, wet, and quite cool.  On the other extreme might be igloos which can take several hours to build, but can last for months and provide plenty of room and stability. 

The Snow Mound Cave

For a medium-fast solution, a snow mound cave may suffice.  I have spent many a winter’s night in these shelters, and have found them warm, quiet, and a little spooky.  These caves depend on snow conditions for stability and some adventurers have died when their poorly built cave collapsed and buried them in their mummy bags.  Not a nice way to go.  When snow conditions are good and there is enough time to make sure the cave is stable, then snow mound caves do provide excellent shelter.  Let’s explore this one in a little more detail.

Snow mound caves can be dug in a snow drift or in a mound piled up for this purpose.  They can only be trusted when the snow is of the right nature to consolidate.  I have had multiple caves collapse on me while under construction because the snow was either too cold and fluffy or had already morphed into sugar snow (hard ice crystals that act more like marbles than snowballs).  If you cannot easily form a quick snowball from the snow, then it will be a challenge to use for a snow mound cave.  For best success, a mound should be built out of non-sugar snow, packed thoroughly layer on layer and then allowed to sit to consolidate for at least an hour before being hollowed out.  This takes a lot of time and only works in emergencies when that time is available.  After hollowing out a cave, heating the cave on the inside and then allowing it to re-freeze will help its stability significantly.  Keep in mind that if you use a drift, you will not know how well packed the snow is.  It might sag down on you or worse during the night.  Also, drifts form in high-wind areas, which are not the best places to build any sort of shelter.

Critical components of a mound cave are:

  • A door a bit lower than your sleeping level.  This allows a pocket of warm air to build up above the door where you will be sleeping.
  • An air vent the size of your arm at the peak of the cave.  This air vent will keep the air fresh and literally save your life.  People can suffocate in snow caves.  This is critical!
  • Walls and ceiling a couple of feet thick or thicker to provide insulation and stability.
  • Room enough to sit up, crawl around, and stretch out for sleeping
  • A door that opens sideways to the dominant winds.  If it is pointed toward the wind, it will act like a wind tunnel and steal your heat.  If it is pointed away from the wind, it could drift completely closed and provide challenges in getting back out.  By pointing the door perpendicular to the wind (or just slightly downwind), the door should not catch the wind nor drift up.
  • The floor of the cave must have a dry tarp or plenty of leaves or pine boughs to keep you from getting soaked by the snow floor.  You will need an insulated sleeping pad to stay warm unless you have a thick pile of leaves or limbs.
  • I usually use a backpack to “close the door” and a candle can be really nice for light and also for heat.

Even on frigid, stormy nights, a properly built snow shelter will maintain temperatures in the 50's just from body heat alone.  This may not seem like the tropics, but it is warmer than a tent, and downright cozy with a winter sleeping bag.

After being warmed all night by body heat, your cave will support many times your body weight, and should last for weeks.
A shortcut to building a mound cave is to dig down into the snow, pile up your packs, and then cover them with about four feet of snow.  Pack the snow as you cover the packs.  Leave the mound to consolidate for an hour or so.  When you come back, dig a low door, and pull the packs out.  This will provide a head start on hollowing out the cave.

Another tip is to bring a complete change of clothes all the way down to the undies.  You will likely get quite wet from sweat and snow while digging out the cave.  Changing into dry clothes is critical for staying warm.

 The A-Frame Snow Cave

The A-frame cave offers some advantages over a mound snow cave, but it is more dependent on the right snow conditions and is not as roomy, making only enough space for one or maybe two people in the best of conditions.  Advantages include being able to build one of these caves without a shovel.  These can be built using only a stick or snow ski for cutting snow.  Also, these caves are lighter, not likely to collapse, and not seriously dangerous if they do.  This shelter is faster to build than a mound cave, and therefore better in emergencies—IF snow conditions allow for it.

To build an A-Frame Snow Shelter, start by packing down a trench of snow about twice as wide as you are and more than twice as long.  Then leave the trench to allow the snow to consolidate.  Even well stomped Champaign powder might consolidate given enough time and the right temperatures.  Warmer snows should pack nicely.  Sugar snow is nearly hopeless for attempting this type of shelter.  Once the trench is firm, cut snow blocks out of the packed floor of the trench using a stick or ski as long as the width of the trench and at least a foot thick and wide.  Once you have cut two, place them on end on opposite sides of the top of the trench and lean them together to form an “A” shaped roof.  Continue making rows of these “A”s until your roof is about a third longer than you are tall.  Then pack any holes in the blocks with plenty of snow and cap the upper end.  Cover the floor of the cave with a tarp and/or pine boughs or leaves.  Make a couple of large blocks for a door.  Be sure to have an arm-sized air hole in the peak of the roof.  The same rules about orienting the door to the wind apply. 

I have used this style of cave a few times, but have found it difficult to build if the snow is too cold to pack well.

The Tarp Trench Snow Shelter

This type of snow shelter is fast and easy to build.  It requires cordage, a tarp, and anchors to hold the tarp in place.  These shelters are warmer than a tent, but not as warm as other snow shelters, and they depend on having enough snow depth to work.  To build one of these, tie cord or rope taut between two trees a couple of feet above the snow.  Then dig a trench about ½ the width of your tarp and a bit longer than you are tall.  The trench should be about three feet deep.  Cover the trench with the tarp over the rope, and anchor the tarp edges in the snow using cord and long sticks or snow anchors.  Then shovel a significant amount of snow on the lower edges of the tarp to seal it up and hold it down.  Use snow blocks to close the head of the tarp and to make a door for the foot.  Again, line the trench with another tarp and insulating materials.

The Tarp Trench Snow shelter is more susceptible to wind noise and wind failure.  However, there is no real concern about collapse, and they can be built in minutes rather than hours.  If time is of the essence, and you have a tarp on hand (after all, it is winter and you would never head into the wilderness without a tarp in the winter, right?), then this life-saving shelter might be your best bet. 

All of these shelters depend in degree on the snow conditions.  If there is not enough snow to build a snow shelter, then opt for a rubbish hut.  In all cases, the key is to start your shelter early – before you need it.  Don’t wait until you are battling hypothermia to get started.  Build the shelter while you are still warm, then relax knowing that the night will pass safely if not comfortably.

With all of these options, choose a location that is sheltered from the wind to build, and one that has plenty of snow.

These snow caves are a lot of fun to build, and if built correctly, a lot of fun to sleep in.  Try making some without planning on spending the night and experiment with different types of designs to accommodate varying snow depths and types.  Get out there with your kids teach them these basic skills.  Nature provides.  Enjoy it!

Please comment with your own snow cave tips.  Do you have any funny snow cave anecdotes to share?

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