9 June, 1999
PERMAFROST 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
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
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 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.
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)
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