Snow avalanches threaten life and property in mountainous areas worldwide. A class 5 avalanche is the largest magnitude avalanche based on the United States classification scale. This type of avalanche is capable of destroying buildings, gouging the landscape, and redefining the topographic parameters of the avalanche path. Large magnitude snow avalanches play an important role ecologically in terms of wildlife habitat, vegetation diversity, and sediment transport within a watershed. Studying large magnitude avalanches is also important in understanding extreme weather events in the context of climate change. In January 2009, a large magnitude avalanche cycle occurred in and around Glacier National Park, Montana. This was caused by rapid warming and rain on snow at mid-elevations, events that are projected to become more common with ongoing climate change. The study site is the Little Granite avalanche path located along the Going-to-the-Sun Road. The avalanche travelled approximately 4000 vertical feet and two linear miles. The rarity of such a large magnitude avalanche and the ease of access to the site provided a unique opportunity to study a large magnitude avalanche event. The objective of the study is to quantify change in vegetative cover immediately after such a large magnitude event and document response over a multi-year period.
Results/Conclusions
Accurate field mapping was completed to determine the redefined perimeter of the avalanche path. Vegetation was monitored using modified USFS Forest Inventory and Analysis plots, and cross sections were taken from over 100 dead trees throughout the avalanche path. An avalanche chronology was developed using dendrochronological methods and compared to an avalanche chronology from other avalanche paths in Glacier National Park. Preliminary results indicate such a large avalanche has not occurred in this path for more than 100 years, and that the topographic parameters of this path were redefined. Stands of large conifers were decimated by the avalanche causing a shift in dominant vegetation types in many parts of the avalanche path. Woody debris up to 30 feet high is now a major ground cover on lower portions of the avalanche path and will likely affect regrowth. Monitoring and measuring the post-avalanche vegetation recovery of this particular avalanche path provides a unique dataset for ecological parameters as well as a case study of an extreme natural hazard event in the context of climate change and infrastructure planning and safety.
