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.

The present mortality as a result of snow avalanches exceeds the average mortality caused by earthquakes as well as all other forms of slope failure combined. Snow avalanches can range from small amounts of loose snow moving rapidly down a slope to slab avalanches, in which large chunks of snow break off and destroy everything in their path. Although considered a hazard in the United States since the westward expansion in the nineteenth century, in modern times snow avalanches are an increasing concern in recreational mountainous areas. However, programs for snow avalanche hazard mitigation in other countries are far ahead of those in the United States. The book identifies several steps that should be taken by the United States in order to establish guidelines for research, technology transfer, and avalanche legislation and zoning.

Avalanches threaten many areas of the world. For many years, risk has been mitigated through artificial avalanche initiation using explosives. Even with extensive use, a lack of experimental determinations of the interactions between explosive detonations and the snowpack response exists. To address this, a multiyear field based research project was conducted at Montana State University, Bozeman, MT. A portable instrument array consisting of pressure and accelerometer sensors was fabricated and utilized to record the overpressure and acceleration of the snowpack resulting from detonation of pentolite cast boosters. Explosives were detonated 0-2 m above the snow surface, at 0.5 m increments. All sensors were placed within a 7 m radius of the explosive in soft slab and hard slab snow conditions. The data was used to characterize relationships between explosive size and location to the resulting overpressure and snow acceleration based on various snow parameters. The snow surface was shown to be able to reflect shockwaves, thus, increasing the shockwave pressure. It was shown that elevating an explosive off the snow surface resulted in greater overpressure and peak snowpack acceleration than surface detonations. Elevating an explosive was found to not influence the vertical or radial attenuation. Therefore raising a charge increased the volume of influence. Overpressure and acceleration were shown to be nonlinearly related to the explosive mass. Doubling the mass resulted in less than double the response. The acceleration of moist snow was determined to be less and the attenuation greater than for dry snow conditions. Hard slab conditions indicated lower acceleration and greater shockwave attenuation than soft slab snow. Snowpack peak acceleration and attenuation were shown to have little dependence on either the total snow water equivalent or snow density. For rock bed surfaces the shockwave was reflected back through the snow while meadow bed surfaces did not. This project verified past theoretical and experimental results, but further research would be beneficial for avalanche mitigation work. A continuation of this work could lead to increased efficiency and safety for the avalanche community.