Snowpack response to directed gas explosions on level ground

Abstract

The artificial release of avalanches is an important mitigation measure in avalanche control. The explosion to trigger an avalanche is either produced by igniting solid (or liquid) explosives or a gas mixture. Whereas there have been several studies on the impact of explosives, there is little research on the effect of directed gas explosions on a snowpack. We performed experiments with a prototype gas exploder above snow and measured air pressure at different distances from the point of explosion and accelerations within the snowpack. By measuring along different directions from the point of explosion we assessed the lateral propagation of the pressure wave caused by the directed explosion. Air pressure decreased distinctly with distance from the point of explosion. For example, air pressure was about (6.0 ± 0.2) kPa at 20 m and (0.59 ± 0.02) kPa at 80 m with 1.8 kg of propane‑oxygen gas mixture. Within a forward cone of half angle of about 37°, the impact was independent of the direction from the exploder axis. Within the snowpack, accelerations decreased distinctly with depth and distance from the point of explosion as it is observed with explosives. The frequency content of the air pressure signal of the directed gas explosion was similar compared to experimental results previously obtained with solid explosives. We conclude that in the gas exploder axis, the impact of a directed gas explosion is comparable to an explosion with solid explosives with similar energy density. Hence, gas explosions are well suited to artificially trigger snow avalanches. In the future, side-by-side experiments will be needed to further analyze differences and similarities between the effect of gas and solid explosives. Moreover, additional measurements at operational gas exploders will allow further validation of the experimental results.