The illustration was created by the Nano Banana Pro neural network.
Historians agree that the first such structures were created over two thousand years ago. A typical igloo has the shape of a dome with a diameter of 2-4 meters, and the height of the snow structure is about 2 meters.
Building an igloo
Igloos are built not from ice, but from blocks carved from dense, wind-compressed snow. This is key, as ice has high thermal conductivity and is a poor insulator, while snow, with its large amount of air between the crystals, is an effective insulator. For snow to be considered suitable, it must be uniform and strong enough to be carved into blocks.
There are two ways to build an igloo: circular and spiral, with the latter being the more common and technically advanced. The blocks are laid in an upward spiral. The largest snow blocks are laid at the base. With each turn, they become smaller and lean inward at an increasing angle, forming a self-supporting structure. This technique allows the walls to hold without additional supports at each stage of construction. The gaps that appear between the blocks are filled with loose snow.
After the construction is complete, the igloo is “heated” from the inside with a fat lamp. The heat causes the inner surface of the walls to melt slightly. The room is then ventilated by letting in cold air. The meltwater that has soaked into the snow freezes, forming a strong ice crust on the walls. This layer seals the seams and gives the structure additional strength. As a result, a properly built igloo becomes so strong that it can withstand the weight of an adult person or even a polar bear.
The entrance to the igloo is a low corridor, the walls of which are also made of snow blocks. The doors are made of animal skins or a large snow block. To get inside, you have to walk along the corridor, sometimes even squatting.
The corridor is often located below floor level, creating a so-called “cold trap.” This solution is based on the laws of physics: warm air is lighter and rises upwards into the living area, while heavier cold air “flows” and is trapped in a low tunnel, preventing heat from escaping.
A skilled person can build a small igloo in less than an hour, given adequate snow. Small igloos are used as temporary shelter, while for long-term residence, Inuit may build structures the size of a small house.
Inside the igloo
The walls of the igloo, made of compressed snow, allow enough diffused daylight to pass through to the interior without additional lighting. In the conditions of the polar night, transparent plates of freshwater ice can be inserted into the wall to provide lighting, which function as windows.
Inuit can form entire villages from igloos, connecting individual dwellings with snow corridors. A large igloo can consist of several “rooms” (individual domes) connected by tunnels, and can accommodate up to 20 people.
For comfort, the floor inside is covered with animal skins, sometimes the walls are also covered with skins. Fat lamps are used for heating and lighting. The heat from them maintains the temperature inside at a comfortable level. For example, if the outside air temperature is -45°C, inside the igloo, only due to the heat of human bodies and the lamp, it can reach from -7°C to +16°C.
Why doesn't the igloo melt?
The stability of an igloo is ensured by several physical principles:
1. Snow as a thermal insulator. The main reason is the low thermal conductivity of snow. Compressed snow consists of 70-90% air. It is the air trapped between the snowflakes that prevents the rapid transfer of heat to the outside. The thermal conductivity of snow (about 0.2 W/(m K)) is comparable to that of wood, while that of solid ice is 10 times higher (2.2 W/(m K)). A building made of ice would be much colder.
2. Temperature gradient. The wall of an igloo is constantly exposed to a temperature gradient—the difference in temperature between the warm interior and the cold exterior. The freezing point (0°C) is located within the wall, not on its inner surface. Heat from the source inside only slightly warms the inner layer, but this meltwater is immediately absorbed into the pores of the snow, where it comes into contact with the colder layers and freezes again. This process is self-regulating and strengthens the structure.
3. Ventilation and humidity. To prevent overheating and excessive melting, as well as to remove carbon dioxide, a small ventilation hole is made in the upper part of the dome. It releases excess warm air. Moisture formed from people's breathing and the burning of the lamp partially condenses on the walls and freezes, and partially exits through ventilation. Thus, the snow walls act as a humidity regulator, absorbing its excess from the air.
4. Dome shape. The spherical shape has the least surface area for a given volume. This means that less heat is lost through the walls of the igloo compared to a rectangular building of the same volume.
At first glance, an igloo is a paradoxical structure. While it is freezing outside and the walls are made of snow, inside people live in whole families. When many igloos are connected by corridors, residents can move freely through such a “village” without having to go outside for a long time, which is important in conditions of severe frost and blizzards.
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