OBSERVATIONS OF PERENNIAL ICE IN ALTERED GEOLOGIC ENVIRONMENTS IN PENNSYLVANIA

In 1898 and 1899, climatologist Edwin Balch visited 33 sites in eastern North America that were known or rumored to retain ice for longer periods of time than was usual for their surroundings. These cold traps (termed “glaciéres naturelles” or natural refrigerators) were found in shaded ravines and gorges, taluses and boulder heaps, as well as in man-made wells, mines and tunnels as far south as West Virginia. Although ice formed in the winter and spring clearly persisted for an unusually long time at some sites, and cold air flowed from the base of talus slopes throughout the summer, no perennial ice was ever observed by Balch. In the current study, we used temperature data loggers to monitor the thermal regime of two cold traps hourly at two sites in Pennsylvania where ice exhibited unusual persistence: these included a man-made exploratory mine shaft and a collapsed anthracite coal mine. Perennial ice was demonstrated at these sites for the first time during the 2014-2015 season. In both cases, the deep man-made recesses allow the accumulation of significant ice relative to the volume and configuration of the cold trap; in summer, thermal stratification of the air mass further minimizes the introduction of warm air and limited the melting of ice. Sufficient annual melting occurred at sites with perennial ice such that little, if any, continuous ice accumulation over longer periods of time would be expected in the current climate without human intervention; at the anthracite coal mine site, ice did not persist through the summer of 2017. Perennial ice in mid-Atlantic states has only been found where man-made alterations of regional geology occur that mimic karst formations where cold traps develop at higher elevations in other parts of the world. These locations seem unlikely to develop perennial ice in years that lack heavy winter snow accumulation and sub-freezing spring temperatures.