Process — Building an igloo from blocks of snow

The diagram illustrates the process by which an igloo is constructed using blocks of compacted snow.

Overall, there are nine stages, which fall into two broad phases: the dome itself is first assembled from pre-cut blocks, after which the shelter is sealed, ventilated and furnished. Interestingly, the structure gains its strength not from any framework but from the spiral arrangement of the blocks themselves.

To begin with, a flat area of hard, well-compacted snow is selected, and large blocks are cut from it with a snow saw. These blocks are then laid in a circle roughly three metres across. Successive rows are added in a spiral, each one leaning slightly further inwards, until only a small opening remains at the top; this is closed with a single key block, which locks the whole dome in place.

Once the shell is complete, a low doorway and a ventilation hole are cut, and soft snow is packed into the gaps between the blocks to seal them. A short tunnel is then built over the entrance to keep out the wind. Finally, the interior walls are smoothed, and a sleeping platform and a small lamp are added, making the igloo ready for use.