SNOW CRYSTAL IMAGING USING SCANNING ELECTRON-MICROSCOPY .2. METAMORPHOSED SNOW

Low-temperature scanning electron microscopy (SEM) was used to observe metamorphosed snow crystals and grains obtained in the field. Metamor phosed snow was obtained from seasonal snowpacks in the Colorado Rocky Mountains and in Alaska. The snow samples obtained in snowpits were m ounted on modified SEM stubs, frozen in liquid nitrogen, transported i n 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 sno w grains with sintering, rounded and faceted crystals, several types o f depth hear, rounded grains of melt metamorphism, and an ice lens. So me 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 ch aracteristics of crystals. SEM appears to have direct application for better understanding of snow crystal metamorphism and snowpack process es, 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 wa ter equivalent.