Adventuring the great outdoors in winter can be a fun and enjoyable experience. However if you live off the grid like I do, winters can be a difficult time and traveling can be hazardous. The only access to and from is by snowmobile and when caught out in a storm, knowing how to build a snow shelter has proven to be very useful.
Step 1: IGLOO
Can be constructed if there is snow of the proper consistency to pack into hard blocks. Keep in mind that building such a shelter takes a great deal of energy and time. Two skilled persons can build a two person igloo in 2-3 hours with proper equipment and good snow. Obviously several such structures would need to be built to hold a larger group. Building an igloo is a process that requires a certain amount of artistry, but is less of an energy expenditure than a snow mound shelter. In general, rectangular blocks roughly 24" by 18" by 6" are cut and stacked in an ascending spiral. The rectangular blocks are placed vertically and the bottom shaped so that only the two bottom corners are supporting the block. Then the block is tilted inward and the vertical edge contacting the adjacent block is cut away until the weight of the block rests only on the upper corner. The weight of the block is supported by the diagonally opposite corners, while the third corner prevents rotation. Once the first row is laid you shave off the tops of several blocks ( 1/4 - 1/3 of the circumference) to create a ramp and build upward in a spiral. Once the structure is complete, snow is packed into all the open joints. (See the Off Belay reprintIgloo.)
Step 2: Snow Mound Shelter
If the party does not have the experience or the snow conditions aren't good for an igloo, a snow mound shelter can be made. In a selected spot, place an upright marker (ski pole, ice axe, etc.) to mark the center. Tie a cord to the marker and scribe a circle in the snow to indicate the pile size. The rule of thumb for size: if the snow in place is not to be dug out, the radius should be the interior size plus about 2 feet; if the snow in place is to be dug out, about 1 foot can be subtracted from the radius for each foot of in-place snow. Piling the snow for a two person shelter will take two people about an hour. Pile loose snow within the marked circle with shovels, tarp etc. Don't compact the snow. When the mound is the right size and shape, do not disturb it; allow it to compact naturally - minimum time one hour. Chances of collapse are greatly reduced if you let it settle for two hours. Thirty-five degrees is the natural angle at which loose snow rests. Be sure to allow the snow to settle at this angle. Otherwise you will have thin spots or a buckling roof when you excavate the interior. After compaction you are ready for digging. The entrance direction should be away from the prevailing incoming weather. From the entrance point start digging toward the marker. Pass the snow out to helpers. As soon as you reach the marker, do no not disturb it. This is your guide for excavating the interior. Clear out the inside to the intended radius. To check on wall and roof thickness, measure with a stick poked through. When the dimensions check, remove the marker and trim the interior. Then install a vent in the roof. Get rid of waste snow promptly before it hardens. The process is a wet one so make sure you have waterproof gear on and good shovels for making the mound and digging out.
Step 3: Snow Cave
A snow cave can be dug into a hillside. Dig the entrance up so that the door is below the sitting level. Also there are natural snow caves formed by the overhanging branches of trees covered with snow. By digging down you can get into the cave beneath the branches. In both cases you should poke a ventilation hole and keep it clear.
Step 4: Snow Pit
This structure can be created by digging a trench in the snow down to ground level (if possible). The structure should be a little longer than your body and 3 - 4 feet wide. Line the bottom with insulative material to insulate you from the cold ground (in an emergency you can use 5-6 inches of evergreen boughs). A roof can be made of skis and poles or overlapping boughs and sticks then covered with a tarp and then loose snow or blocks of hard pack snow. The doorway will be a tunnel in from the side. This can be plugged with a door of hard pack snow. A ventilation hole must be poked into the roof for air flow. Keeping a stick in this hole and shaking it every so often will keep the hole open. If possible, the entrance should be lower than the level of the trench, this keeps the coldest air in the entrance rather than in the trench.