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9 June, 1999PERMAFROST TUNNEL/LOESS/ICE WEDGES/PERMAFROST/ I haven't had a chance to tell you much about the permafrost tunnel that I had the opportunity to visit last week - it was only mentioned in the June 8th journal. CRREL's (Cold Regions Research and Engineering Laboratory) Permafrost Tunnel is located 10 miles north of Fairbanks in Fox, Alaska. Permafrost is ground that has been frozen for 2 or more years. Although Fairbanks and the surrounding areas have areas without permafrost (discontinuous permafrost), where the tunnel has been dug is completely frozen. To get into the tunnel, you must first go through a wooden door at the entrance to keep the cold air in during the summer. It is refrigerated during the summer, and during the winter it is cooled by natural CONVECTION - cold air passes through the inside and out a ventilation shaft at the end of the 360ft long tunnel. They also use fans to move the cold air as far back into the tunnel as possible. Lights are strung up throughout the entire tunnel, but they are used as little as possible because of the heat that RADIATES from them. The first thing that I noticed upon entering the tunnel (besides the cold!) is the SMELL! There is a musty, decaying type of smell that comes from all of the organic matter in the ceiling, floors, and walls, which dates back to 40,000 years ago. The tunnel is a very unique place. It was first made to try out different types of mining in frozen ground. Within the walls are frozen ponds, ice wedges, and bison bones. As we walked through the tunnel, we created a little dust storm by stirring up the LOESS, which is a very fine sediment which is blown by the wind and collects everywhere in that area. ICE WEDGES Ice wedges are just what they sound like. They are formed when the ground contracts in cold weather, forming a network of cracks which are polygon shaped (many sided). They form polygons, from my understanding, just because it is a natural shape to fracture under stress - it is the shape of least resistance. The tundra is covered with these polygon shapes, bordered by ice wedges, which collect more water during the summer melt of snow and thus grow bigger and deeper. They start as small ice veins, but over thousands of years grow to form large wedges. I think that polygon shapes are seen on Mars as well, which is evidence of past climate and weathering of the terrain there. (I don't know this for sure, though! Someone could tell me more about it!) In Antarctica, an area called Dry Valleys shows the same polygon shapes on the ground, as well. PERMAFROST PROBLEMS In areas where there is permafrost, there is normally some thawing that happens near the surface, at varying depths. This layer that thaws is called the "active" layer, and causes some problems for people who are building structures upon permafrost. Often, surface structures sink; in Barrow, houses are built on stilts, to reduce the surface area that is on the ground. At the permafrost tunnel, parts of the tunnel are beginning to close themselves off. I think Matthew Sturm, who was our guide through the tunnel, called the slow sinking of the ceiling "permafrost creep". Alaska must spend quite a bit of money repairing roads in the spring when this active layer begins to thaw! If you have any questions about permafrost or the permafrost tunnel, be sure to email me, and I will do my best to find out the answer for you! Michele Hauschulz (Teacher Experiencing the Arctic Program) ____________________________________________________________________ Get your own FREE, personal Netscape WebMail account today at http://webmail.netscape.com.
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