Q. Peggy wants to know – exactly what is permafrost, and how much is it melting?
A. Hi Peggy: Permafrost results when the temperature in rock or soil remains below freezing throughout the year. It forms when the below ground temperature cools sufficiently in winter to keep it frozen even when the season changes. As to how much it is melting, that is difficult to say.
Usually a permafrost area can have a layer on top that is called the active layer. It freezes in winter, but thaws in summer. Below that is the permafrost layer, which stays frozen. The thickness of the permafrost layer and the active layer can change depending on local climate, for one thing. I don’t think there is any doubt that our world climate is changing. When we first moved to Wasilla 18 years ago, each winter would bring some below zero weather – like maybe a week or so at a time of 20-30 below zero. Over the past years that has changed so that now we seldom have very much below zero. Usually the winter temp hangs around zero F. or maybe 10 below, and that only lasts for a couple days at a time. A nice change for sure.
They (the infamous ‘they’) figure that permafrost underlies 50% of Russia and Canada; 82% of Alaska; 20% of China, and all of Antarctica. The permafrost in northern Siberia is 5,250 feet thick!
Permafrost presents unique problems in building projects in the north – but leave it to man to figure out how to do something. To keep your building from heaving around as the permafrost changes, sometimes small buildings are just put up a few inches on pilings so that there is airflow under them; thus insulating the permafrost from them. Large buildings will have insulated foundation pilings sunk deep into the permafrost so that they don’t change. Of course the ideal is just to find a spot to build that is on bedrock, or well drained soil with low ice content.
When we came to Alaska in 1971, we expected the whole state to be these tall towering evergreen trees. We were a bit disappointed to find the black spruce in the area we moved to (Copper River Basin) were these short, stunted, rather funny looking trees. Upon inquiring we found the reason was their toes were growing (or rather trying to grow) in permafrost! We discovered the tall trees like we were expecting are in the areas of the state which are relatively free of permafrost; such as the lower panhandle of Alaska.
Our highways up here are continually changing because of the permafrost heaving up and down in some areas. That’s why tourists often find our roads full of ‘dips’, but don’t get too used to where a particular bulge or dip is in the highway – because next week it could have changed positions. There is a lot of road repair going on in the summer. We Alaskans have a saying in fact: There are only to seasons in Alaska. Winter…..and Road Construction!