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.
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 Unpublished MSc thesis, in Geography, University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.