MULTI-YEAR STATISTICAL ANALYSIS OF AVALANCHE ACTIVITY ON THE VAUGHAN LEWIS ICEFALL, JUNEAU ICEFIELD, ALASKA
Direct observation of avalanche activity on the Vaughan Lewis Icefall, Juneau Icefield, Alaska, was conducted. A simplified data set of magnitude, time and location was compiled and statistically analyzed, showing an inverse relationship between relative frequency and avalanche magnitude. Significant diurnal variation in avalanche rates per hour were observed. Prediction of avalanche effects on successive avalanches (induced avalanches) was also verified.
METHODS:
During avalanche observation, time and estimated magnitude were recorded. In order to reduce the complexity of the data set, time was recorded in half-minute increments and magnitudes were estimated by teams of trained observers and categorized into a 10-division scale. The data were plotted along with a best fit curve of the form f=0.23m^(3/2) where f is the frequency and m is the avalanche magnitude. The data set for avalanche frequency was collected into one hour intervals for analysis which shows a statistically significant diurnal variation. A Poisson distribution of the form p(x;μ) = (e^(-μ))*(μ^x)/x! describes the predicted avalanche activity where p is the probability of x avalanches in a one hour time interval, and μ is the overall mean or expected value for that particular time interval.
SUMMARY RESULTS:
Relative avalanche frequency is shown to vary inversely proportional to the magnitude of the avalanche. A statistically significant diurnal variation for avalanche activity was detected with the peak activity occurring in the early morning hours. This actively is postulated to occur due to the ambient air temperature falling below the freezing level and the associated refreezing of melt water entrained throughout the icefall. Vibration and movement within the icefall immediately following an avalanche event were shown to induce successive avalanches. This activity was most likely to occur in the first 2 minutes and after 4 minutes the effects of the previous avalanche were no longer statistically significant. Follow-on research could include similar analysis of other icefalls in both temperate and non-temperate glaciers. Direct application of this research could lead to mountaineering techniques designed to reduce the significant hazards associated with glacier travel though icefall regions.