Where the Great Whale River empties into the Hudson Bay, it is intrenched in the Tyrrel Sea sands (altitude : about 30 m) and in slightly older glacio-marine clays. On the left side of the river, this materials is eaten away by a dozen hemicycles. This morphology has been produced, during the last two milleniums by the succession of five different processes : 1) slow solifluxion, 2) thermokarstic subsidence, 3) nival sheet-wash, 4) sudden flowage, in the presence of concave faults, 5) gentle mud flowing. Certainly nivation has been as important a factor as the melting of permafrost in this nophogenesis.