DENDROGEOMORPHIC ANALYSIS OF AVALANCHE CHUTES IN THE ROCK CREEK VALLEY, BEARTOOTH MOUNTAINS, MONTANA, U.S.A

Snow avalanches are a common hazard in mountainous areas and represent a threat to human life and property, especially in the wildland-urban interface. More data for past incidents are necessary to better estimate risk in such areas, especially where historical records are lacking. One way to obtain these data is through evidence found in the tree-ring record. As proven recorders of past conditions and events, trees have been used to reconstruct geomorphic events for over a century, and the science of dendrogeomorphology has been defined and formalized for decades. In the United States (US), tree-ring evidence has been used to study avalanches throughout the country, but few US studies have been conducted in recent years and most have concentrated on select areas, such as Glacier National Park. This study initiates dendrogeomorphic work in a region unstudied since 1969, and will provide data to aid in the evaluation of avalanche risk for the Rock Creek Valley of Red Lodge, Montana, a popular tourist destination and ski town. The primary objective of this preliminary study is to use methods in dendrogeomorphology to develop an avalanche history for a site in the Rock Creek Valley. We used multiple lines of tree-ring evidence to detect simultaneous growth disturbances, including growth suppression and/or release, scarring, reaction wood/ring eccentricity within the trunk, patterns of secondary succession, and tree mortality. We used variable thresholds for absolute and relative simultaneous growth reactions based on sample size and depth, as well as a control chronology developed from unaffected trees, to isolate avalanche events from other disturbances and/or climate. At this point, only preliminary results are available, but suggest a return interval of approximately 10-20 years, with the most recent event occurring in 1997. Work continues, to develop an avalanche history for the Rock Creek Valley site, and to initiate new dendrogeomorphic projects in the region.