It's All About Heat What is Permafrost? Permafrost is defined as ground that has been at a temperature below the freezing point of water for more than two years. A large portion of the ground in Alaska is defined as permafrost (some estimates say as much as 80 percent). Permafrost can extend to a depth of several hundred feet, or it can be as little as several feet deep. Is there permafrost in Fairbanks? Yes. We live in an area defined by "discontinuous" permafrost. This classification refers to the fact that some of the ground is frozen, and some of it is not. Also, it is important to note that the permafrost in this area is known as "warm" permafrost. Warm permafrost is at a temperature of approximately 31.5 degrees F .In other words, if it got just a little tiny bit warmer, it would melt (and by definition, it would no longer be permafrost.) So what's the big deal if it melts? Well, possibly nothing. By definition, bedrock that is beneath the freezing point is considered to be permafrost. If this were to thaw, there would be no catastrophic results for the structures that sit on top of it(frozen gravel deposits also remain relatively stable after thawing). When assesing the fragility of permafrost, we must consider the soil type. Much of the perrenialy frozen ground in our region is composed of a silt type material with an extremely high moisture content (30-50 %). In fact, there is so much moisture that there are actualy large hunks of pure ice enveloped by the soil. When ground of this composition thaws, it loses it's strength. Any roads or structures that may sit on the surface are subject to sink, often with devastating results. This is a cool picture. Though slightly garbled, it shows a dozer building road over an ice lens. This gives you a good idea of the permafrost structure. The general rule of thumb in this situation is get that thing covered up quick. In other words, limit the thermal contact, we can't let that thing melt. THINK OF IT LIKE THIS Let's say you were going to build a road. You probably wouldn't build it through the middle of a swamp. A swamp is a wet, mushy, unstable quagmere of mud. A road built in these conditions would be sure to fall apart and crumble into ruins in quick time. It would be a foolhardy thing to do. Yet if the swamp was frozen, and hidden by a facade of shrubs, you would probably build a road over the top. The swamp in its' frozen state would be suprisingly strong, and would have no problem supporting a road embankment. Believe it or not, much of the permafrost encountered in Alaska can be accurately likened to the frozen swamp. It is all right to build on it- just pray that it doesn't melt. Now, let's get down to buisness... The disfunctional relationship between asphalt and ice