The effects of explosives on the physical properties of snow

Abstract

Explosives are a critically important component of avalanche control programs. They are used to both initiate avalanches and to test snowpack instability by ski areas, highway departments and other avalanche programs around the world. Current understanding of the effects of explosives on snow is mainly limited to shock wave behavior demonstrated through stress wave velocities, pressures and attenuation. This study seeks to enhance current knowledge of how explosives physically alter snow by providing data from field-based observations and analyses that quantify the effect of explosives on snow density, snow hardness and snow stability test results. Density, hardness and stability test results were evaluated both before and after the application of 0.9 kg cast pentolite boosters as surface and air blasts. Changes in these properties were evaluated at specified distances up to 5.5 meters (m) from the blast center for surface blasts and up to 4 m from the blast center for air blasts. A density gauge, hand hardness, a ram penetrometer, Compression Tests (CTs), and Extended Column Tests (ECTs) were used. In addition to the field based observations, the measurement error of the density gauge was established in laboratory tests. Results from surface blasts did not provide conclusive data. Air blasts yielded statistically significant density increases out to a distance of 1.5 m from the blast center and down to a depth of 50 centimeters (cm). Statistically significant density increases were also observed at the surface (down to 20 cm) out to a distance of 4 m. Hardness data showed little to no measurable change. Results from CTs showed a statistically significant decrease in the number of taps needed for column failure 4 m from the blast center in the post-explosive tests. A smaller data set of ECT results showed no overall change in ECT score. The findings of this study provide a better understanding of the physical changes in snow following explosives, which may lead to more effective and efficient avalanche risk mitigation.