I spent last weekend in the Sierra Mountains in Northern California, I decided to use some of this time to build a winter survival shelter. The igloo in the picture to the right was the result of many hours cutting, shaping, and assembling blocks of snow.Location: Alpine County, CA
Elevation: 7400 ft above sea level
Tools required: Snow Saw, shovel, Ski Poles, length of nylon cord.
I chose to build the igloo in a clearing on a south facing slope about halfway between the valley floor and the ridge, the prevailing wind was coming from the North, the entrance was built to face away from the wind to prevent excessive drafts through the structure.
In order to create a circle pattern for the igloo foundation, I used two ski poles and a 4 ft. length on nylon cord as a makeshift compass. The result was better than expected, a circle that was nearly perfect.I then began the task of harvesting the frozen snow. The snow was acceptable, but is was not perfect. Some of the snow had been exposed to the sun and melted and was frozen again, this caused several of the blocks to break.
When the snow has been compressed and frozen, the tool of choice would be to use a snow saw, because the snow was relatively soft I was able to use a specially constructed wooden board to cut the blocks of snow. I would carry the rough blocks to the structure and shape them to fit with the edge of a snow shovel. Each time I added a block to the igloo I would place it closer to the center so that it would over hang and produce a smaller opening. Each block is cut into a partial wedge so that is fits snug to the block it is being placed beside, the prior block is helping to support the block which allows you to hang the block further out. 
I cut each block to the same initial dimensions, and the result was a fairly large block of snow, this really helped the igloo take shape right away, but caused the igloo to grow rather tall, toward the end of construction I actually used the snowmobile sled as a scaffold, so that I could place the final pieces to enclose the roof. Next time I intend to use the spiral method, where you shape the first layer like a ramp so that you can construct the igloo in one continuous coil. I will also use shorter blocks to that the height doesn't present a problem. This igloo was more than 8 feet tall on the outside when I finished. I could actually stand inside of it. The inside dimensions were large enough to shelter at least three adults comfortably.
The conditions were fairly mild while I built the igloo, the temperature was in the upper 30's I decided to test the igloo and spent a couple of hours inside the igloo after dark with a tarp, and several blankets. I found that I was rather comfortable, but chose not to spend the night because the inside surface was not smoothed out and my body heat and the candles that I was burning were producing alot of drips. Overall I really enjoyed the experience, I learned alot about the construction of igloos, and I look forward to the next one. Since building this igloo the area received a massive snow storm that dropped four feet of snow. I wonder if the igloo survived.
Adventure note: We spotted two coyote around the entrance of the igloo the following morning, we watched them as they made their way to the ridge, and even saw them attack a black squirrel.
