Date of Thesis
Bachelor of Science
R. Craig Kochel
Jeffrey M. Trop
Ice-dominated mass wasting processes from deteriorating alpine ice-caps are constructing icy debris fans at outlets of incised bedrock catchments along valley glaciers margins. Previous short-term field observations provided limited understanding of the nature and rate of depositional processes. Recent eight-month time-lapse imagery (January - September 2013) permits the investigation of frequency, area, and volumetric contributions of mass wasting deposits to seven fans in the Southern Alps of New Zealand. Time-lapse imagery and field observations document remarkably high depositional rates, primarily by ice avalanches (83-98%). Debris flows, slush flows, and rockfalls all account for 2-17% of recorded events. Time-lapse imagery only records major events that emerge onto fans, but direct field observations also document smaller events that occur within the catchments above the fan apex. During nine months, two fans at La Perouse Glacier received 308 major depositional events covering 2675% of the fan's surface areas (ranging from 653 to 2022% per fan). During eight months, five fans at Douglas Glacier received 646 events covering 6151% of the fan's surface areas (ranging from 313 to 2102% per fan). The field observations made at La Perouse recorded seven events on two icy debris fans over two days. At Douglas, field observations recorded 210 events on five fans over two days; more than >90% of these were in the catchments. Frequency of ice avalanches correlates with deposit area, but areas vary significantly. It is not uncommon for five to seven depositional events to cover >50% of a fan area. On especially active days, deposits may cover 80 to >100% of fan surfaces. For the first time, the evolution processes of icy debris fans has been documented over several seasons, providing information on the dynamics of contributed material to valley glaciers annually. Ice avalanches occurred throughout the observation period, but the pace decreased during winter. Most depositional events occurred after significant rainfall. However, in warmer months the icecap melting may have been the primary cause of ice avalanches in the absence of rainfall. Debris and slush flows were only mobilized after major rainfall. At both sites, differences in timing, frequency, and depositional process types between fans are attributable to variations in catchment morphology and linkages to the ice/snow supply in the nÃ©vÃ© regions.
Reid, Mattie Morgan, "Mass Wasting Processes, Geomorphic Response, and Seasonal Variation of Icy Debris Fans on the La Perouse Glacier and Douglas Glacier, Tai Poutini, Westland National Park, Southern Alps, New Zealand" (2015). Honors Theses. 325.