Glacial geomorphology, fluvial geomorphology, hillslope geomorphology, submarine geomorphology, tectonic geomorphology...

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Tuesday, 28 September 2010

NZ-YD#2: Maybe the Waiho Loop is a climate signal

Kaplan et al., (2010), Figure 2. Central Southern Alps about 13 000 yr ago
Michael Kaplan is back in the New Zealand Younger Dryas debate this week, as coauthor with Aaron Putnam et al. in Nature Geoscience. This investigation of the Birch Hill moraine, again using 10Be cosmogenic dates, shows that the Antarctic Cold Reversal (ACR) did cause glacial advance in the Pukaki catchment at 12.97 ka and a similar expansion of the nearby Macaulay glacier, so the ACR is likely to have been a Southern Hemisphere-wide cooling event. This provides further weight to the bipolar seesaw hypothesis; simply that one hemisphere cools whilst the other warms. These results also correspond to a climatic driver for the Franz Josef glacier advancing to form the Waiho Loop moraine, rather than the landslide origin proposed by Tovar et al., (2008) amongst others, as evidence against a Younger Dryas in New Zealand. A climate origin for this moraine would indicate ACR cooling in New Zealand that occurred asynchronously to the Northern Hemisphere YD. So was New Zealand warm or cold between 13-11 ka? An ongoing discussion...

Tuesday, 14 September 2010

Occasional YouTube video #7 - Debris flow with car-sized clasts

Speaks for itself... (action starts around 1:09)

As posted on Dave's Landslide Blog, where it was suggested by Ivan Montanari. Atrani lies in a reasonably precarious position on the Amalfi coast in Italy.

Monday, 13 September 2010

NZ-YD#1: No evidence for a Southern Hemisphere Younger Dryas?

Irishman's Stream, New Zealand
The presence of a Younger Dryas (YD, ~13-12 ka) cooling event in New Zealand has been much discussed as it would provide a useful correlation to the Northern Hemisphere cooling at this time, and so indicate if glacial-interglacial cycles in either hemisphere occur synchronously or sequentially. South Island's Waiho Loop moraine was previously considered to represent the YD, but recent research by Tovar et al. at Canterbury University revealed its landslide origin. A paper in Nature this week by Kaplan et al. has shown from an investigation of glacial events in Irishman's Stream, using very high resolution 10Be dating, that this glacier retreated consistently throughout the period of the YD. This suggests that during a Northern Hemisphere glacial the Southern Hemisphere is warming, which may be due to a southward shift in warm climate systems, or a more extreme seasonality between the poles during cooling. In fact, our understanding of the climate of this area is changing rapidly; Shulmeister et al. extend the start of the Last Glacial Maximum in New Zealand by 2 kyr to ~24 ka, again using cosmogenic dating.

Sunday, 12 September 2010

Do glaciers reset the luminescence signal of the sediment at their base?

Haut Glacier d'Arolla, Switzerland
Lots of interesting discussions at last week's UK TL/OSL/ESR conference at Oxford University, but of particular interest to geomorphologists was Mark Bateman's talk 'Do glaciers reset their beds?'. Mark told us about the work that he and Darrel Swift are doing at Sheffield to investigate the effect of subglacial transport on the luminescence signal of basal sediments, which is about to be published in Boreas. Darrel drilled a core through the Haut Glacier d'Arolla, Switzerland to collect sediment from its base for initial luminescence measurements. Then they moved the lab, using a ring-shear 'donut' machine to recreate subglacial stresses on quartz sand with substantial known luminescence characteristics.This indicated that increased strain increases the number of zero dose grains and reduces the overall paleodose of the sediment. So yes, it would appear that glaciers do reset their beds, raising the possibility of using luminescence to date glacial retreat stages and sediment transport to a high resolution.