| Summary: | With an increase in use of New Zealand's alpine terrain, there is a growing need to
understand processes and phenomena associated with snow avalanche hazard. This
research investigates snowpack structure and meteorological influences associated
with avalanching at Porter Heights Ski Area and overviews the management practices
employed in response to this hazard. Data sources are derived from meteorological
and snowpack observations dating back to 1977, coupled with comprehensive field
studies in 2003.
Weak faceted and mixed crystal forms were found to comprise on average over 40 %
of the early season snowpack on sunny and shaded slope aspects, although they could
persist on shaded slopes throughout the season, contributing to spring avalanche
events. The growth of both lower pack depth hoar, and near-surface facets were
strongly influenced by synoptic airflows. Forty-eight hours after the onset of a cool
southeast airflow, the temperature gradients in a shallow snowpack ranged from -0.36
°C cm-1 near the surface, to -0.17 °C cm-1 deeper in the pack. A warmer northwest
flow induced surface melting, and dramatically altered the thermal regime of the
snowpack.
Thick layers of rounded grains indicated the importance of equilibrium growth and
wind redistribution of snow. Wind loading is most extensive on slopes leeward to the
prevalent, strong, west to northwest winds, and slab formation in this terrain is
regularly controlled using hand placed explosives and ski cutting techniques. Density
measurements centred on a median value of 185 kg/nr' suggested the significance of
decomposing new snow in forming surface slabs, with the largest snowfalls at Porter
Heights occurring during east to southeast storm events. While this study has
cemented a comprehensive understanding of meteorology and snowpack structure at
Porter Heights, backcountry avalanche forecasting in the neighbouring terrain will
further benefit from larger scale, collaborative future research initiatives.
|
|---|
