It is a good idea to dig a trench knee deep or more inside your vestibule to help get into and out of your tent. This should be filled in before you leave. If the wind changes or you can’t get out of the wind it is possible to build a shelter around the tent using snow blocks.
Commence by marking out a circle of the diameter you require on flat ground— about 2.5 m is a minimum, but up to 4 or 5 m will accommodate up to five or six people. Cut blocks of snow about 300 × 300 × 600 mm long, and lay them outside the circle. Cut the blocks from outside the igloo—do not lower the floor level, as cold air will drain in. Igloos are built as a spiral, and the door is cut at the end. After laying, the first layer of blocks must be cut to form the base of the spiral, by trimming them so that the top slopes inwards, with the height increasing smoothly and gradually from ground level to the full height of the block by the end of the layer, as shown in Figure 13.1.
Continue laying blocks as you move around the spiral, always leaning them inwards. The last block will be round and conical—like a cork from a large jar. The door is cut next to last, and then a protective tunnel can be built. Once inside, smooth the inside very carefully, as any low points will drip. Any cracks should be filled with snow from the outside.
A snow shovel, a pruning saw or a plywood platform used to support your stove could be used to help build or cut blocks. Rubber washing-up gloves are also useful for handling the snow blocks. Snow construction can be hot work, so don’t forget to drink while working.
Digging a cave in a deep bank of snow can produce a comfortable and secure living space if conditions are ideal. However, in bad weather or unstable snow it can be a dangerous venture. In 1999, near Mt. Kosciuszko, New South Wales, a group of snowboarders died in a snow cave they had dug.
Snow caves are built by digging into a large snowdrift or bank. Dig an entry tunnel, starting at the base of the drift, initially in horizontally, then angling upwards. When in about 600–900 mm, start digging the cave upwards and out on each side. One person should dig the cave inside, while another will be needed to clear the entry tunnel of snow from the cave. The floor of the cave should be above the top of the entry tunnel, so cold air cannot drain in. Smooth the roof very carefully, as any low points or bumps will drip. Make a ventilation hole in the roof with a stock. Snow cave construction is very hot, very wet work, and good waterproof jackets, overpants and mittens are essential.
Leaders should be aware of some serious risks associated with snow caving. If the cave is made too large or the snow is soft and wet, the roof may collapse onto the occupants. A cave should be no larger than is necessary to provide sleeping space and the roof should be carefully domed. If any cooking is done in the cave, then good ventilation must be provided, with the entrance lower than the sleeping platform and a ‘chimney’ to permit exit of steam and carbon dioxide and carbon monoxide. If the entrance is higher than the cooking area then carbon monoxide, which is heavier than air, may settle in the lower portion of the cave and can threaten the lives of the occupants.
If fresh snow falls through the night it is highly likely that the entrance to the cave will be filled with snow. A total blockage can lead to suffocation. It is useful to keep a stock or other suitable tool inside the cave to create air holes in the roof if needed. Where a cave is dug into a slope which has distinct layers of snow, a large slab of unstable snow could break away and slide down the mountain taking skis or any other gear with it. The occupants of the cave may find themselves exposed to the elements or the entrance to their cave may be blocked by the slide. Both these have occurred in Australia. One group lost important gear in the slide, which was effectively a small avalanche. All things considered, a good snow tent, well pitched in a sheltered site or with windbreak walls built around it is generally a safer shelter.