Knowing how to build a snow wall or snow shelter is a useful, almost essential, skill for winter adventuring. Understanding how snow holds together—and how you can speed up the bonding process—can help you find or create the best, most cohesive snow for your construction needs.
Snowflakes are delicate structures with lots of thin points radiating from a central node. If they are disturbed, the points are broken off and the snowflakes compact together. The energy from this disturbance briefly melts the edges of the squashed flakes, which then freeze together to create a cohesive snow mass. This process, known as sintering, is what happens when you compress snow to make a snowball in your hands.
The same process also occurs when snow is blown by the wind. As the flakes fly through the air and bounce along the surface, their points are broken off. When they settle, they bond together to form a solid unit, also known as a wind slab. The same effect occurs if you disturb snow by shoveling it or stomping it down with your feet.
Sintering also occurs as snow goes through melt-freeze cycles—the snowflake points melt off, the snowpack settles, and then the whole thing refreezes as temperatures drop. Because snow is a poor conductor of heat, this effect typically only occurs in the uppermost inches of the snowpack.
If you're going to build a snow wall or construct a snow shelter like an igloo, you need solid snow blocks for building. To find them, you can look for consolidated wind slabs (though these are often hard to find in forested terrain where snow blows only short distances), find a strong bonded layer on top of the snowpack, or start the sintering process yourself.
Stomping the snow underfoot is one of the easiest methods to create snow blocks. Find an open area of recent, undisturbed snow and repeatedly walk around on top of it until it no longer compresses. Snowshoes are ideal for this, though you can accomplish the same thing (albeit more slowly) with just your boots.
Once the snow is flattened, you need to let it sit for a little while to allow sintering to take place. The rate sintering occurs varies depending on the temperature and moisture content of the snow. Wet snow close to the freezing point bonds quickly; drier snow in low temperatures takes longer. In most conditions, the snow will sufficiently bond together in an hour or less.
Keep in mind, however, that in extremely cold weather or in very dry snow conditions, sintering may not occur at all. If the temperature or moisture content is too low (these two factors are closely linked), the energy created by disturbing the snow will be insufficient to melt the snowflakes for refreezing. Think of the loose, powdery snow that won't bond together for a decent snowball to fling at your buddies.
Once sintering has occurred, it's time to dig out some snow blocks. The best tool for this is a snow saw, a specialized tool designed specifically for this purpose. (One of the best is the 6-ounce G3 Bonesaw.) Next best is the blade of a snow shovel. If you have neither, you can improvise with a snowshoe or ice axe.
If you're interested in learning more about snow shelter construction, check out this excellent and comprehensive snow shelter field manual from the U.S. Antarctic Program.
“Equipped” is an AMC Outdoors blog, written by Matt Heid.
Top image courtesy of Polar Discovery.
Labels: Shelters, Winter