Have you ever sloshed through a big mud puddle in the springtime? Or have you ever slopped through icky, gicky mud? You end up with mud caked on your shoes and your mom yelling at you not to track all that mud into the house – right? Maybe you are like me and think, “It was so much easier a few months ago when it was all frozen!”
Watching the ground thaw and freeze is as much a part of the yearly cycle as starting a new school year in the fall and finishing in June. There are some things that just… are.
Yet in many areas around the globe, the ground never does thaw out. Rather, it remains frozen throughout the year and has its own set of characteristics. This ground is called the permafrost and is very common in the Arctic tundra.
How does the permafrost happen?
In the winter, temperatures plummet and the ground freezes to a certain depth – that depth is dependent on many factors:
- air temperature
- what kinds of plants
- how many plants there are in the region
- how much snow falls
- what kind of soil it is
- how well water can drain out
In most regions on earth, the ground thaws out in the spring and summer, but in some areas – mostly way up high in the mountains, or in the arctic and antarctic regions, the ground never does completely thaw. In these regions there will be a thin layer of soil on top that thaws – called the active layer. The depth of the active layer is dependent on the same factors as listed above, and will affect life in the area dramatically. The part of the ground that never thaws out is called the permafrost.
How can plants grow in the permafrost?
They can’t. Plants can only grow in soil that thaws at least part of the year, which means they can only grow in the active layer. The type of plants that can grow in areas with an underlying permafrost layer are very distinctive. Given the harsh conditions of the arctic tundra, there aren’t a whole lot of plants that can survive there. Plants you will find growing in the harsh permafrost soil tend to:
- be small
- have shallow root systems
- grow grouped together to resist the winds
- have flowers with a fuzzy coating to protect them from the wind
- produce flowers quickly because they have a very short growing season
- some flowers are cup-shaped to direct the sun’s rays into the center of the flower for warmth
How does the permafrost affect construction?
Imagine building a shack on the ice in the middle of the winter. Then imagine leaving that shack there once spring comes. What would happen? The ice would melt and the shack would sink to the bottom of the lake. That’s a lot like what happens when you try to build on the permafrost. Building on permafrost is difficult because the heat from the building (or pipeline) will melt the permafrost and the building will sink into the mud.
This problem has three common solutions.
- using foundations on wood piles: You can drill holes deep into the frozen layer and place ‘stilts’ down into the holes, then build your building on top of those stilts. If your stilts are deep enough that the heat from the building will never reach that far, the ground under the stilt will remain solid and continue to hold up your building. Depending on where you are, you may need to dig down fifteen meters or more! That’s about as far underground as a two story building is tall!
- building on a thick gravel pad: Sometimes engineers choose to place the building, road, or pipline on a thick layer of gravel. The layer is generally one-two meters thick – that’s about as thick as a normal person is tall! By using the gravel, the heat from the structure does not reach the permafrost layer.
- using anhydrous ammonia heat pipes. The Trans-Alaska Pipeline System uses insulated heat pipes to prevent the pipeline from sinking. These specially designed pipes transport heat away from the ground into the air.