Discrimination of hot versus cold avalanche deposits: implications for hazards assessment at Mount Meager, British Columbia

Abstract

Avalanche deposits within the Mount Meager volcanic complex are nearly monolithological and comprise mainly intermediate volcanic rock clasts up to 10.5 m, lack internal structure, and are very poorly sorted. Despite these physical similarities, the deposits originate from two distinct processes, cold rock-avalanche deposits from mass wasting and hot block-and-ash avalanche deposits derived from gravitational collapse of active lava domes and flows. Hot block-and-ash deposits are recognized by the presence of features indicative of high emplacement tem- peratures. Clasts within rock-avalanche deposits preserve predepositional weathering and jointing surfaces as well as fragmentation surfaces from transport. The ability to discriminate between hot and cold avalanche deposits and the recognition of multiple volcanic events are critical to hazard assessment in volcanic terranes. Misidentifica- tion can lead to underestimating the risk of one (i.e. volcanic) hazard whilst overestimating the other (i.e. mass wasting).