Snow avalanche regime and climatic conditions in the Chic-Choc Range, eastern Canada

Because snow avalanches occur at altitudes close to the 0A degrees C isotherm in mountain environments, they should respond quickly to climatic variations. This study provides tree-ring-based high-magnitude avalanche chronologies for 12 subalpine avalanche paths in the Chic-Choc Range of Qu,bec (eastern Canada). For the period covered by the chronologies, i.e., between 1895 and 1999, high-magnitude avalanches occurred with an average return interval of 5.3 years, which represents an average annual probability of 21% for all paths. A regional avalanche activity index (RAAI) was developed to help differentiating widespread regional avalanche activity from avalanche events resulting from local factors. Nineteen years of high-magnitude avalanche occurrence were identified (1898, 1936, 1939, 1941, 1965, 1969, 1970, 1971, 1977, 1981, 1984, 1987, 1988, 1989, 1990, 1991, 1992, 1994 and 1995). Of these, 15 occurred after 1950 and 10 after 1980. Propitious climatic conditions that account for widespread avalanche activity in the study region were identified as follows: (1) above-average total snowfall, (2) high-frequency of snowstorms, (3) major rain events and facet-crust development, (4) sequences of freezing rain and strong winds, and (5) early-season weak layers of faceted crystals and depth hoar. The number of days with air temperature above 0A degrees C has strong implications on the internal structure and stratigraphy of the snowpack, and consequently on avalanche release. Land managers should thus consider more closely the impact of climatic conditions and warming on avalanche activity.