AbstractThe Sand Hills moraine of southwest Banks Island is extensively affected by backwearing thermokarst in the form of ground ice slumps. Most are initiated by coastal erosion, with the result that 75% of the land within 100 m of the coastline has been transgressed by slumps. The majority are polycyclic and typically less than 200 m in length. Mean headwall retreat rates are between 8.6 and 11.4 m/a, although a maximum of 15.5 m/a was recorded for one slump in 1983–84. On average, slumps are active for 12–15 years, a substantially shorter time than in the moraine belt of eastern Banks Island (French and Egginton 1973). Surface lowering rates due to backwearing thermokarst in a strip of land within 1 km of the coast, are estimated to be up to two orders of magnitude greater than probable denudation due to slopewash and solifluction processes.