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Title: Re-evaluating the deglacial sequence in New Zealand – part 2 - sudden ice collapse or gradual retreat?
Authors: Shulmeister, J
Fink, D
Hyatt, OM
Thackray, GD
Rother, H
Keywords: New Zealand
Issue Date: 15-May-2009
Publisher: GNS Science
Citation: Shilmeister, J., Fink, D., Hyatt, O. M., Thackray, G. D., & Rother, H. (2009). Re-evaluating the deglacial sequence in New Zealand – part 2 - sudden ice collapse or gradual retreat? Paper presented at the Past Climates meeting, Wellington New Zealand, May 15-17, 2009.
Abstract: New data on moraine formation and glacial valley chronology challenges the existing understanding of the nature of deglaciation in New Zealand. When the glaciers retreat from glacial maximum limits they drop behind their fan heads and this creates accommodation space. This almost invariably leads to the formation of a pro-glacial lake system during retreat. Where the glacier trough is well developed deep lakes are formed. This results in an apparent collapse of the ice margin as floating ice leaves no terminal moraines. In contrast, if an over-deepened trough is not present, the glacier retreats in a stepwise fashion up valley with many terminal positions created (though not always preserved). At Rakaia Valley ice retreated less than 10 km in 10,000 years from its glacial maximum position. In dated east coast systems, the subsequent timing of ‘ice collapse’ differs from valley to valley. The chronology of deglaciation in New Zealand indicates that apparent ice collapse occurred at different times in different valleys during the deglaciation but this is largely an artifact of the timing of proglacial lake formation. Instead of ice collapse during the early part of the deglaciation followed by a significant very late glacial (ACR/YD) re-advance, we propose that extended ice remained in valleys with high elevation catchments until after ~15 ka. There is no major ice collapse prior to this time. Subsequently a minor ice re-advance occurred in these systems, which might relate in timing to either the ACR or YD. It may alternatively reflect a change from a calving terminus into a proglacial lake back to an outwash fan head system. In either case this event is of minor significance.
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