MULTI-SCALE ANALYSIS OF AVALANCHE DYNAMICS AROUND MOUNT WASHINGTON, NEW HAMPSHIRE

Mount Washington is an important destination for winter recreational activities, since it is the highest summit within a day’s drive of more than 70 millions people. Every year, there is an average of 25 people who are injured while climbing or skiing. Snow Rangers of the United States Forest Service (USFS) have been issuing snow avalanche advisories for the past 55 years on Mount Washington. However, until now, no scientific investigation focused on the avalanche dynamics of this region. The objective of this study is to use data at different spatiotemporal resolutions in order to better understand the snow avalanche dynamics of Mount Washington with a systemic perspective taking into account topographic, ecological, climatic and meteorological factors.

This study provides the first tree-ring analysis in northeastern United States, in order to assess the chronology of low-frequency, high-magnitude snow avalanche for 7 avalanche paths of different aspects around Mount Washington for the period determined by the oldest trees (±100 years). More than 400 trees were sampled in the runout zone. The chronology was created by linking growth disturbances found on tree rings such as scars, reaction wood and abrupt growth reduction to the year of occurrence. This chronology served as the basis to create a regional avalanche activity index (RAAI) and identify years of high-magnitude avalanche activity. Climatic scenarios that account for these events are proposed. The age-structure of the forest in each couloir is linked with the recurrence interval of high-magnitude avalanche.

This research project will give the first insights into the climatic drivers of avalanche activity at local (individual avalanche path) and regional scales (Mount Washington) of northeastern United States, which could lead to a better knowledge of snow avalanche dynamics and more precise and widespread forecasts by the USFS Snow Rangers.