| Summary: | The climatic and geomorphic factors affecting retrogressive thaw slump initiation and activity on the Aklavik Plateau (Richardson Mountains, NWT) were examined using historical air photographs over a 54‐year period (1950 to 2004). In this region, thaw slumps include a near‐vertical headwall, a floor of low gradient (2–10°) and a steeply sloping evacuation channel (15–25°) that connects the floor of the thaw slumps to Willow River located 60–150 m below. All thaw slumps on the Aklavik Plateau are located within the glacial limit of the Laurentide Ice Sheet and the majority developed on the western side of the valley on gently sloping terrain. Aerial photographic analysis showed an increase in thaw slump initiation from 0.35 new thaw slump yr−1 over the 1954–71 period to 0.68 new thaw slump yr−1 over the 1985–2004 period. This increase follows the pattern of the 10‐year running mean summer air temperature record over the 1950–2004 period. However, the total number of active mature thaw slumps on the Aklavik Plateau decreased from a maximum of 46 in 1950 to a minimum of 24 observed in 2004, which follows, to a certain extent, the 10‐year running average of rainfall. Both these trends may relate to the influence of climate on the erosional processes that are thought to initiate thaw slumps and keep them active in regions of highlands. Copyright © 2009 John Wiley & Sons, Ltd. and Her Majesty the Queen in right of Canada.
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