This article is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Larry Gedney is a seismologist at the Institute. You would think that unless it is replenished in some way, it should eventually be broken up and knocked aside, or maybe just sublimated away. In all, I have polled at least 20 individuals and come up with almost as many different opinions.
Different causes seem to predominate, depending on the circumstances.
Most of the responses could be listed as falling into one of three broad categories which sometimes overlap. The first is that the thin layer of ice is simply the compressed remnants of an earlier layer of snow or freezing rain. Often, this is the obvious case, but it fails where the roads have been clear for a period of time before the ice appears and there has been no precipitation. The second is that the ice is produced when moisture from automobile exhaust condenses and collects on the road surface. However, this is not a realistic mechanism on the open road where vehicle speeds are such that exhaust gases quickly evaporate.