Alpine Permafrost in the Contiguous United States: A Review

Although permafrost exists in the high plateaus and high mountains of the contiguous United States, little precise information is available about its occurrence. About 100,000 km2 of alpine permafrost is present in the western United States from Washington to Arizona. Some of this permafrost probably is not in equilibrium with the present climate; however, there are no temperature data to support this statement. Long-term air temperature data measured at high altitudes are scarce, because most meteorological stations are situated in valleys.Alpine permafrost occurs only where the mean annual air temperature is 0°C or lower. Evidence of perennially frozen ground in the higher mountains of the western United States consists of negative ground-temperature measurements below the active layer for more than 2 yr, ice-cemented rock glaciers, and ice lenses, granules, and pore fillings in the ground. The present alpine permafrost zone in the western United States was much larger in Wisconsin time than it is now, and the 0°C mean annual air temperature isotherm was about 1000 m lower. At present, the latitudinal gradient of the elevation of the lower limit of alpine permafrost between 30 and 50°N latitude is 80 m per degree of latitude in the United States.Now that more exploration for oil and minerals is being undertaken in high plateaus and high mountains and construction of transportation and communication lines and recreational facilities is increasing there, more information about alpine permafrost is needed. Systematic studies of alpine permafrost have already been initiated in the western Cordillera in Canada; similar studies should be undertaken in the United States.