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Ice loss at the terminus of the Tasman glacier

Jennifer M. Purdie
Department of Geography, University of Otago, Dunedin, New Zealand

 
Abstract

This study investigates long term ice loss due to climate warming at the terminus of the Tasman glacier. This ice loss is measured in the lowest 4 km² of the glacier, hereafter referred to as "ice loss at the terminus". In the past ten years the glacier has gone from an ablation regime of melt under the debris and around sinkholes, to one where calving into the lake is now important. Rates of ice melt at bare ice slopes and beneath the extensive debris layer are measured over one summer. These are related to measured climate variables. Also measured is ice loss due to calving into the proglacial lake. Surveys are made of changes in the glacier surface, and of depth and temperature in the lake.

Melt of ice is greatest on bare ice slopes, averaging 96 mm.d-1 of ice depth over the summer period. Melt under the debris averaged 7 mm.d-1, and calving accounted for a specific ice loss of 125 mm.d-1. Overall, calving is the most dominant form of ice loss at the terminus accounting for 73% of the total. Melt under the debris layer accounted for 26% of terminus ablation, and melt on bare ice slopes just 1%, due to the relatively small area covered by these. Ice loss at the terminus is therefore largely de-coupled from climatic influences, and due mainly to the effect of the proglacial lake.

A total amount of 21.3 x 106 m³.a-1 of water is estimated to be lost from the terminus area. 135 x 106 m³.a-1 of water is estimated to be lost from the wider area below Ball Hut, with 20% of this being from calving at the terminus. This proportion will increase as the glacier terminus retreats up the valley. This study predicts the terminus will be situated at Ball Hut (approximately 10 km upglacier) in 135 years. Long term stored water being released from the Tasman Glacier is resulting in a mean annual flow into Lake Pukaki of 4.3 m.s-1. The water released from glaciers in the Pukaki catchment due to glacier recession is 6% of the annual inflow to Lake Pukaki.

 
Reference

Purdie, J.M. 1996. Ice loss at the terminus of the Tasman Glacier. Unpublished MSc thesis, in Geography, University of Otago, Dunedin, New Zealand. 191 pp.

© 2009 Department of Geography, University of Otago, Dunedin, New Zealand