The Mass Balance of Selected Glaciers of the Southern Alps in New Zealand
The mass balances of Brewster, Glenmary, Park Pass and Rolleston Glacier in the Southern Alps of New Zealand were investigated. To study the mass balance, an integrative approach was chosen that included direct mass balance measurements, aerial oblique end-of-summer snowline (EOSS) photos and a mass balance model. The main focus was on the maritime Brewster Glacier where a field-based mass balance programme was initiated with extensive direct measurements and installation of an automatic weather station (AWS). For the years 2005–2008, the net balances were 1141 mm water equivalent (mm w.e.), 282 mm w.e., 297 mm w.e. and -1653 mm w.e. with mass balance gradients at the ELA ranging from 7 to 14 mm w.e./m. With the direct measurements, a mass balance model of an intermediate complexity was calibrated. The model is based on a simple numerical mass balance model that combines elements from energy-balance and degree-day models and uses daily climate data as input. The three tested climate datasets were climate station data from the CliFlo database, an interpolated climate dataset from Andrew Tait and the ERA-40 reanalysis climate data. To downscale the climate datasets to the conditions at Brewster Glacier, the measured climate data from the Brewster AWS was used. After the model calibration the mass balance was modelled for the past three decades. For the validation of the modelled mass balance and snow cover, photographed EOSS, a geodetic survey and a parameterisation scheme were used. The EOSS records are from annual surveys that have been conducted since 1977 by taking oblique photographs of 50 index glaciers from a light aircraft. In the past, these records have been used as a proxy for the mass balance under the assumption that the EOSS represents the equilibrium line altitude (ELA). Modelling the mass balance for 30 years was difficult because of inhomogeneous climate data and almost non-existing high altitude climate data. However, the measurements, modelling results and the geodetic survey indicated that the mass balance was positive from 1986–1997, negative from 1997–2007 and negative for the entire period from 1978–2007. The modelled and measured mass balance also showed that the length of the ablation season varies remarkably in New Zealand. This highlighted the problematic use of the EOSS records as mass balance proxy because the photographs are usually taken in early March which is sometimes well before the actual end of summer. Additionally, the ELA is defined from the mass balance curve versus the altitude which is closely linked to the temperature, whereas the EOSS altitude is derived from the accumulation-area versus altitude distribution and in some cases from the size of snow patches. Limited mass balance measurements were also taken on the transitional Glenmary Glacier and the maritime Park Pass and Rolleston Glacier. It was found that Glenmary and Park Pass Glacier were retreating and that Rolleston Glacier was stationary. At Glenmary Glacier, the mass balance was strongly influenced by wind induced snow drift. While Park Pass Glacier’s ablation and retreat is enhanced by ice calving into the proglacial lake, Rolleston Glacier’s mass balance is relatively stable because the accumulation area is fed by avalanches. This PhD study has been initiated because in 2002 no ongoing long-term mass balance programme existed in New Zealand. Now, Brewster Glacier is one of the mass balance glaciers included with detailed information in the Glacier Mass Balance Bulletin of the World Glacier Monitoring Service, which indicates the significance of Brewster Glacier in the worldwide context.
Advisor: Fitzsimons, Sean J.; Cullen, Nicolas J.
Degree Name: Doctor of Philosophy
Degree Discipline: Department of Geography; Department of Geography
Publisher: University of Otago
Keywords: mass balance; glacier; Brewster Glacier; Southern Alps of New Zealand; mass balance measurements; mass balance modelling; Glenmary; end-of-summer snowline; Rolleston; Park Pass
Research Type: Thesis