Near-surface Faceted Crystal Formation and Snow Stability in a High-latitude Maritime Snow Climate, Juneau, Alaska

The City and Borough of Juneau, Alaska, has several major avalanche paths located in close proximity to population centers and is routinely affected by avalanche activity. As a result, developing a better understanding of the snowpack conditions that lead to avalanche cycles is of great interest. This study investigates temperature and vapor pressure gradients associated with near-surface faceted crystal formation in the highlatitude maritime snow climate of southeast Alaska. Here we report on two episodes in March and April 2003 in which temperature gradients measured in the upper 25 cm of the snowpack were in excess of 708C m . These temperature gradients were associated with strong near-surface vapor pressure gradients that exceeded 5 mb m 1 for up to 48 h. During both episodes, faceted crystals 1–2 mm in diameter were observed to form near the surface of the snowpack. Field tests performed simultaneously at the study site demonstrated pronounced instabilities associated with the newly formed faceted crystals. Furthermore, avalanche activity was observed following both periods. Investigations of proximate avalanches showed that wind-loaded dry slabs were running on layers of nearsurface faceted crystals.