Permafrost and Thermal Anomalies in Talus Slopes near Thunder Bay, Ontario

摘要

Local knowledge, BTS measurements, and observations of interstitial ice suggest the presence of permafrost in talus slopes near Thunder Bay, ON. The nearest known permafrost is 400 km to the north. Mean annual air temperatures in the region are less than 2.5℃, similar to and lower than other locations where permafrost has previously been found in blocky materials. In order to determine whether permafrost exists in talus slopes in the region, ground temperature sensors were installed at the bottom of two talus slopes to measure conditions at the surface and within the talus for two years beginning on 15 October 2016. Interstitial ice at these sites was - monitored over the same period in summer and autumn. Mean annual surface temperatures were -4.0℃ and -5.8℃ and mean annual temperatures in the talus ranged from -4.3℃ to -7.3℃. During the winter, talus surface and internal temperatures fluctuated in response to multi-day trends in weather, with mean freezing season temperatures below -9℃. During the thawing seasons, the sites experienced prolonged zero curtains. Mean thawing season temperatures were below 2℃, and lower than 0℃ at several internal sensors. Bodies of interstitial ice persisted into the autumn at both sites. The temperature record and observations of the interstitial ice indicated the presence of permafrost at the bottom of one of the slopes.