The response of Ka Roimata o Hine Hukatere Franz Josef Glacier to climate change
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
In the past century global climate warming has led to widespread glacier recession, which in turn has made a significant contribution to eustatic sea level rise. In the coming century, warming is projected to continue and small glacier melt will make a further contribution to sea level rise. In the monitoring of global glacier change and prediction of the response of glacier to climate change, the few well-studied Southern Hemisphere glaciers have an important role to play in elucidating global climate linkages, both in the information that they have left on past climate and glacier change, and the information the provide on future changes to the cryosphere. Franz Josef Glacier, with the best record of terminus position in the Southern Hemisphere, has an important place in assessing global climate and glacier change. The aim of this thesis is examine the response of Franz Josef Glacier to climate change. This goal is achieved through the application of coupled mass balance and ice-flow models, verified with an extensive set of field measurements. A range of previous studies have attempted to understand the linkages between climate and the advance and retreat of the glacier. Methods of examining the response of the glacier have progressed from simple correlations of climate variables and terminus position, to coupled mass balance - ice-flow models. Despite the large amount written about the glacier, there have been few direct measurements of ice velocity, almost a complete lack of mass balance measurements and no measurements of ice thickness. Without these measurements it is difficult to have confidence in the output of the models. A comparison of the output of these models indicates a wide range of predicted mass balance and ice velocity, the two essential components of glacier response to climate change. The programme of field measurement indicates that Franz Josef Glacier has an extremely high mass turnover. Ablation at the terminus is more than 20 m/a w.e. and accumulation in the névé up to 7 m/a w.e. A degree-day mass balance model is able to simulate these measurements, but measured mass balance at the same elevation varies significantly, indicating that the assumption that the only spatial variation of mass balance is with elevation may not be valid here. Ice velocity reaches 2.5 m/day, which is high for a midlatitude glacier. Temporal variations in velocity measurements indicate that basal sliding occurs year round with little seasonal variation, and a greater sliding velocity on the glacier tongue than in the accumulation area. An ice velocity model tuned to the ice velocity measurements confirms this pattern of sliding velocity. vii The coupled mass balance and ice-flow simulates the overall 20th century glacier retreat, but does not simulate the terminus response well, a result of the mass balance model not producing accurate results for the period 1894-1940. The model, when run for a short period of time into the future, indicates that glacier response is independent of climate for a period of 5 years, and that Franz Josef Glacier will almost certainly retreat a further 1 km in the next 5 years. Longer term predictions are dependent on climate change scenarios, such that by 2100 the Franz Josef Glacier could be anywhere from a size similar to the present to two small glaciers perched on the highest peaks. The mean scenario indicates that by 2100 the glacier will have lost 20% of its volume and retreated 4 km to terminate near the present day Almer Glacier. The possibly significant recession of the Franz Josef Glacier will have an impact on the local community and economy with recreation and tourism on the glacier becoming much more difficult. While the results of this study are particular to Franz Josef Glacier, they provide information on how other small glaciers respond to climate change.