KnowHow team explains: The igloo, a temporary winter hunting shelter for the Alaskan Eskimo, does melt inside, but not to a great extent.

The snowflakes falling outside of the igloo, in the harsh Alaskan winter, quickly melt when they land on the roof, providing a replacement layer of insulation. This ongoing freezing and re-freezing hardens the structure, and transforms the blocks of snow the Eskimos used in the construction process into a solid, icy, domed refuge.

The initial freezing and re-freezing take place at end of the igloo’s construction. First, the men must dig a trench into a fresh snow-drift and using their knives, cut blocks of snow from it that are specifically shaped to face inward when fully laid out. They then lay the blocks on their edges to form a circle, cutting them to size as they go, so that the end result will be a narrowing spiral. They cap the igloo by dropping a block with edges cut wider above than below, into the remaining gap in the roof, and “grout” the gaps between blocks of snow with additional snow.

The men then call in the resident expert, the Eskimo woman, to lend the finishing touches. Armed with her whale blubber lamp, she enters the structure, lights her lamp to the highest possible setting, beats a hasty retreat, and seals the entrance with a block of ice. Inside the igloo, the snow on the roof begins to melt but, because of its domed design, the water melts down the sides of the shelter, and soaks the blocks of snow. When the blocks are almost completely saturated with water, the Eskimo woman returns, douses the lamp, and allows the frigid outside air to rush in, transforming the fragile snow structure into one of hard, solid ice.

The igloo is now prepared for its temporary tenants, whose body heat, combined with the warmth of one to two blubber lamps, maintain its interior at approximately 13°C. Not until the winter ends, and the exterior temperature rises, does the igloo begin to melt. Hopefully, the Eskimos will be long gone by then, as the igloo will collapse — dome-first!

The question was sent by Kaushik Basu via email