Stress measurements in the weak layer during snow stability tests

Abstract

The snow compression test is a snow stability test where an isolated column of snow is progressively loaded by tapping on it to induce failure in a possible weak layer. The test result provides valuable information about the propensity of failure initiation within the snowpack. However, different persons might tap with different force and thus reduce the reproducibility of the test results. The aim of this work was to quantify the influence of different test persons and different snowpacks on snow compression test results. We therefore let 62 persons tap on a stress measurement plate during a workshop of the European Avalanche Warning Services. Moreover, in the field, we performed stress measurements during 116 snow compression tests with 13 persons at eight different locations in the Alps. Data on persons’ body features and snow properties were also collected. Our results show that the stresses that reach a weak snow layer due to tapping are influenced by both the snowpack as well as different persons. Still, the data's scattering is surprisingly small for lower loading steps and decreases with depth. Therefore, we can deduce that, especially when avalanche conditions are particularly dangerous, snow compression test results are quite reproducible.

How hard do we tap during snow stability tests?

“…This is an improvement over similar studies that used a sampling rate of 100 Hz. (Griesser et al 2023) and 105 Hz (Thumlert and Jamieson, 2015).…”

“…However, variability in magnitude and duration of applied force will result in some variability of the stress state within the snow which may lead to variability in test results. For more on this topic, we refer the reader to studies by Napadensky (1964), Wakahama & Sato (1977), Johnson et al (1993), Schweizer et al (1995), van Herwijnen & Birkeland (2014, Thumlert & Jamieson (2015), and Griesser et al (2023).…”

“…Thumlert and Jamieson (2015) impacted the snow with both a drop hammer and hand taps and measured the resulting stress within the snow. Griesser et al (2023) measured the impact force from 62 participants from the European Avalanche Warning Services, as well as a field-based study where they measured stress within the snowpack.…”