We investigate how temperature gradient and initial density influence depth-hoar growth in snow and seek to better define the range of conditions under which cohesive, or hard, depth hoar forms. Samples of 400 kg m-3 sieved snow were exposed to temperature gradients of 20-80°C m-1, and samples of four different densities were exposed to a 40°C m-1 temperature gradient. Following exposure to temperature gradients, penetrometer tests were made on samples to determine the presence of solid and/or hard depth hoar. Grain bond orientation was analyzed in section planes by two-dimensional stereological techniques where hard depth hoar developed. Results indicate that hard cohesive depth hoar forms from rounded-grain snow having a density of 400 kg m-3 or greater, following exposure to a temperature gradient of 20°C m-1or greater. Hard depth hoar appears to consist of solid-type depth-hoar grains connected by necks, with vertically preferred directions of grain elongation and organization of grain-to-grain chains. This work corroborates Atikaya's (1974) results, but extends his observation of formation of hard depth hoar to weaker temperature gradients for high-density snow. Our results also indicate that hard depth hoar is composed of faceted solid-type (anhedral) grains.
The Journal of Glaciology is published six times per year. It accepts submissions from any discipline related to the study of snow and ice. All articles are peer reviewed. The Journal is included in the ISI Science Citation Index.