AEOLIAN DUST TRANSPORT AND DEPOSITION BY FOEHN WINDS IN AN ALPINE ENVIRONMENT, LAKE TEKAPO, NEW-ZEALAND

Observations from an automatic weather station and anemograph network are used in conjunction with recorded dust deposition rates to identif y principle sources of wind blown dust within an alpine lake basin. Me teorological observations made throughout the study indicate that foeh n windstorms provide ideal conditions for the initiation of aeolian pr ocesses, including dust storm genesis. A mean wind speed during foehn windstorms of 7.5 m s(-1) at 2.65 m above the surface was observed to initiate entrainment of dust particles from geomorphically active area s within the lake basin, particularly from the dry braid channels of g lacier fed rivers, exposed lacustrine deltas and degraded tussock gras slands. This threshold entrainment velocity is similar to others prese nted within the international literature for such surface types. A diu rnal modulation of meteorological parameters monitored during foehn wi nd events suggests that aeolian processes, such as dust entrainment, a re most likely to occur from late morning to early evening. However, w here topography enhances wind speeds, for example by channelling airfl ow down river valleys, favourable conditions for dust entrainment may prevail throughout the night in the absence of precipitation. Potentia l dust roses were determined for two sites within the lake basin. The dust roses supported anecdotal and observational evidence of principle dust sources within the study area, and appear to be an effective too l for identifying the potential hazard to a particular location from b lowing dust, once the physical trigger conditions for dust entrainment are known. This requires detailed and concurrent monitoring of metero logical variables in association with dust transportation and depositi on rates, especially in complex terrain where many micro-climates ofte n exist.