A STEADY-STATE MASS-BALANCE MODEL FOR THE FRANZ JOSEF GLACIER, NEW ZEALAND: TESTING AND APPLICATION

P>We describe a simple steady-state mass-balance model for the Franz Josef glacier, South Island, New Zealand. Instead of using an ice-flow rule in the model, a simple basal-shear-stress rule is calibrated to yield glacier surface slope as a function of ice depth. We test the model against known temperature cooling constraints required to emplace the Little Ice Age moraines. We then use our model to represent the reduction of ablation due to a rock avalanche falling on to the ablation zone of Franz Josef glacier about 10 000 to 13 000 years ago; it shows that at the temperature prevailing at that time (< 2 degrees C cooler than at present, according to proxy data), rock avalanche debris covering a proportion of the ablation zone could cause an advance of the glacier from near Canavan's Knob to the Waiho Loop. By contrast, the 5 degrees C cooling required for a purely climatically-driven advance to the Loop contradicts proxy data. These findings are of significance to the ongoing debate on the climatic significance, or otherwise, of the Waiho Loop Moraine. The simple approach to glacier modelling developed in this study has the potential to test the effects of climate change and rock avalanches on glacier behaviour easily and effectively in glacial environments worldwide.