Permafrost is a layer of rock or soil that remains frozen yearround. Unlike seasonal frost, which freezes and thaws with the seasons, permafrost stays frozen even in the summer. Some areas of permafrost are covered by what's called an active layer that's really just seasonal frost atop permafrost. About 20 percent of the land on earth contains permafrost, with about half of the permanently frozen ground occurring in Russia. The rest of the permafrost is spread between Canada and Alaska.
How do you think the permafrost of the Arctic ecosystem affects building practices? Find out with this frozen ground activity.
1. Mix the gravel, soil, water, and moss in the plastic container.
2. Place the container in the freezer or outside until frozen.
3. Meanwhile, shape the clay into a house, using the toothpicks for corner support.
4. Once the soil mixture inside the container is frozen, bring it inside/remove it from the freezer and place the clay house atop the soil.
5. Place the container in a sunny spot—like a windowsill— and allow it to thaw slowly. Observe the soil and the house at periodic intervals, making a note of how they look and how they change as the mixture thaws.
Ecosystems are a community of living organisms existing in complex relationships with one another and their physical environment. Those organisms include everything from plants and animals to bacteria and human beings. The physical environment includes weather patterns, natural resources, and soil. In places like Alaska and Siberia, permafrost is a vital component of the ecosystem, and humans have learned to adapt building practices to accommodate it.
When constructing a house or a building on permafrost, problems arise when the once permanently frozen ground begins to thaw. So what causes permafrost to thaw? Natural weather patterns occurring over time, clearing a building site of trees (and the shade they provide), and heat from the structure itself can all cause permafrost to melt.
Instability of the ground supporting a structure's foundation can cause the building itself to sink and shift, its pipes to burst, its windows to crack, and its door frames to warp—all compromising structural integrity. You probably observed some of these with the clay house you made.
To combat these challenges, structures built upon the permafrost of the Arctic and Antarctic ecosystems utilize several foundation types beyond the typical poured concrete. Smaller buildings can be erected upon a six-foot-deep gravel pad that provides insulation from the permafrost's active layer.
Wood piles driven into holes melted into the permafrost are another option. Once set within the permafrost, the piles are left for a year to allow the ground to freeze around them, anchoring them in place. Then the structure is built above the ground to allow circulation and minimize heat transfer. The clay house we built was similar to this method.
A final method involves piles or tubes filled with antifreeze. With these Arctic building methods in mind, try repeating the project. This time, erect the clay house atop the soil before freezing, and/or conduct several freeze/thaw cycles to see how that affects stability. If you like, use a thermometer to record soil temperatures throughout the activity.
Project adapted from: http://www.pbs.org/edens/denali/permawht.htm