Time Series Analysis of Acoustic Emission Measurements from an Experimental Avalanche Slope at Patsio in Great Himalaya

Abstract

Snow avalanches are formed due to the failure of a weak layer buried below a cohesive snow slab. Microscopic failures due to progressive damage within the snow release elastic waves known as ‘acoustic emissions (AEs)’. Attempts were made to monitor AEs prior to snow slope failure to obtain a potential tool for non-invasive snowpack stability assessment. We present acoustic emission measurements from a natural snowpack present on a test slope near Patsio field observatory located in Indian Himalaya. Time series analyses of AE parameters such as amplitude, counts and energy were carried out for the observation period. Snow related additional data such as snowpack evolution, snowstorms and pit profiles were also recorded to interpret the AE response of natural snowpack. The snowpack on the test slope was monitored continuously to observe any fracture or slope failure. We found an increased AE activity with loading during snowfall. For some of the events, distinct energy peaks were recorded simultaneously by all AE sensors. These high energy events may be attributed to the formation of large cracks within the snowpack. The amplitude-frequency distribution data of AE events were further analyzed, and the temporal variation of the b-value was estimated. We then tried to relate the temporal evolution of the b-value with the occurrence of cracks observed on the surface of snowpack. However, no clear pattern emerged. The b-value decreased toward the fracture event but overall showed strong fluctuations during the snowstorm.