Moraine's rock type gives rise to questions about synchronistic climate change

Reprinted from the University of Canterbury's "Chronicle" - 19/12/08

New findings by three University of Canterbury researchers could pour cold water on evidence that climate change is happening simultaneously around the world.

The discovery was made as a result of a study of the Waiho Loop glacial moraine, on the plain between Franz Josef township and the sea, and was described by co-author Professor Jamie Shulmeister as throwing "a cat among the paleoclimate pigeons".

"There has been a huge scientific debate on the climatic implications of the Waiho Loop and this rather changes the debate," he said.

A moraine is a ridge of debris deposited by a glacier marking the extent of an earlier advance by that glacier. Scientists have thought the Waiho Loop moraine was created during a brief cold snap about 13,000 years ago which also affected Europe and North America, and inspired the Hollywood blockbuster movie The Day After Tomorrow.

The Waiho Loop moraine is widely used as evidence for direct inter-hemispheric linkage in climate change. But the new findings suggest the loop was the result of a landslide, not climate change.

Professor Shulmeister, who worked on the research with Associate Professor Tim Davies and honours student Daniel Tovar, said there had been a huge scientific debate on the climatic implications of the Waiho Loop. But no one had ever studied its sediments.

Research by Professor Jamie Shulmeister (left) and Associate Professor Tim Davies has shed new light on the Waiho Loop. Photo source: UC Chronicle Click here to view a larger version

"When graduate student Dan Tovar had a look he discovered to our surprise that it was mainly made up of a rock type known as greywacke which is different to the rocks that make up all the other moraines in front of the Franz Josef glacier.

"This rock type occurs about 13km up the valley from the Loop. All the other moraines are predominantly composed of schist, which outcrops near Franz Josef township. The greywacke was also rather more angular than the rocks in the other moraines, suggesting it had not been transported in water or at the base of a glacier.

"In order to get lots of angular greywacke rock to the moraine without diluting it with lots of schist, it must be carried on top of the glacier. The easiest way to do this is to have a large landslide well up the glacier in the greywacke zone dump a huge volume of rock on top of the glacier."

As a result of its findings, which have been published in the prestigious international science journal, Nature Geoscience, Professor Shulmeister's team believes a large landslide dumped a huge volume of rock on top of the glacier causing it to advance and, when the advance stopped, the moraine was created.

He said his team had considered the cause of the landslide.

"The South Island's Alpine Fault line runs through the Franz Josef township and we think it is a likely candidate. Our next move is to see if we can come up with more general means for separating landslide generated moraines from climatic ones ­ and we think we can.

"If we can do this then we may be able to use these glacial moraines as a tool to examine past earthquakes and this may ultimately contribute to hazard management in high mountain areas."