Snow crystal imaging using scanning electron microscopy: II. Metamorphosed snow

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Abstract
Low-temperature scanning electron microscopy (SEM) was used to observe metamorphosed snow crystals and grains obtained in the field. Metamorphosed snow was obtained from seasonal snowpacks in the Colorado Rocky Mountains and in Alaska. The snow samples obtained in snowpits were mounted on modified SEM stubs, frozen in liquid nitrogen, transported in Dewar flasks to the SEM facility, sputter coated with platinum, and imaged with an electron beam. Analysis of a representative set of snow samples revealed examples of metamorphosed stellar crystals, fine snow grains with sintering, rounded and faceted crystals, several types of depth hoar, rounded grains of melt metamorphism, and an ice lens. Some of the crystals exhibiting both rounding and facets indicated that both equitemperature and temperature gradient metamorphism influenced the snowpack. The SEM methods developed are operable in the field and can be used to quantify three-dimensionally size, shape and bonding characteristics of crystals. SEM appears to have direct application for better understanding of snow crystal metamorphism and snowpack processes, increasing knowledge of conditions leading to avalanche formation, and improving modelling of the transfer of microwave energy from the ground surface through the snowpack for eventual estimation of snow water equivalent.

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