Permafrost landform degradation over more than half a century, Macmillan/Caribou Pass region, NWT/Yukon, Canada

Aerial photography, ground photos and descriptions from the early 1940's have been supplemented by sequential aerial photography and field sampling to examine permafrost landform degradation over more than 25 years. Seven study sites, extending over a distance of 75 km and an elevation range of 550 in, have been intensively monitored since 1990 and regular reconnaissance-level visits have been made to an additional 91 features. Features indicative of degradation were evident on the earliest aerial photography and on ground photography from the same period. Without exception, peatlands with palsas and peat plateaux have continued to experience permafrost-landform degradation, including the complete decay of some features, areal reductions, and the development of thermokarst depressions. Degradation rates, established from sequential photography, average 1% per annum over the last half century. However, it is possible to find features that are degrading along one margin but are stable or possibly aggrading elsewhere. The regional nature of permafrost degradation suggests that climatic factors initiated processes of permafrost degradation sometime between 800 and 1944 AD.