Re-evaluating the deglacial sequence in New Zealand – part 2 - sudden ice collapse or gradual retreat?
Loading...
Date
2009-05-15
Journal Title
Journal ISSN
Volume Title
Publisher
GNS Science
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.
Description
Keywords
New Zealand, Glaciers, Ice, Lakes, Valleys, Levels
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.