Photogeologic Study of Periglacial Talus Glaciers in Northwestern Canada

Abstract

In the Norman Wells area, precipitous escarpments at two localities are flanked by fossil composite talus glaciers of unusual size, extent, configuration, and topographic setting. The term, piedmont talus glacier is proposed as descriptive. Talus is supplied by the disintegration of massive Silurian limestone, and merges downward into broad continuous aprons of rubble marked by transverse and longitudinal ridges and furrows in varied patterns. Outward extent is up to 1000 m, and the outer margin is irregular to strongly scalloped. Lateral extent is up to 14 km, with a few gaps. Volume of material is estimated to represent cliff recession on the order of 60 m. The surface now is entirely stabilized, except for an upper fringe of new, active talus overlapping the older talus.

Occurrence in an area of former continental glaciation excludes ice of valley glaciers as a genetic factor. Pseudo-glacial movement by gradual, differential mass movement, conditioned by a former periglacial environment, is the only satisfactory basis for explanation. Ensuing stabilization is attributed to climatic amelioration, with diminution or cessation of frost weathering which supplied talus.

Present size and extent is interpreted provisionally to represent the cumulative effects of two episodes of formation, one pre-Hypsithermal and one early Neo-glacial. Observed stabilization is assigned to the ensuing part of Neoglacial time until interrupted in latest Neoglacial time by reneval of talus building still in progress, reflecting another climatic shift toward conditions more favorable for frost weathering. These relationships provide new data for interpretation of Postglacial climatic chronology in the area.