Glacier detectives

A fairly busy last few months has involved proposal writing, lab work, seminar presenting and even some fieldwork, this time just down the road (relative to my Antarctic expedition). This fieldwork was part of a fellow blogger’s PhD project, focussed on mapping evidence of past glaciers and ice caps in New Zealand’s Tongariro National Park (a cultural and natural World Heritage Site). The work is part of a larger GNS mission, which also includes mapping the area’s volcanic past, and the result should be similar to what has been achieved in the central Southern Alps.

Mapped glacial moraines in the Southern Alps (GNS)

“That sounds interesting, but what’s the point?” Well aside from informing the public and helping tourists envisage glaciers in the valleys and mountain slopes where they now trek, it’s also important for piecing together New Zealand’s evolving climate. There are some records of past climate from marine and terrestrial indicators, including evidence of much more extensive glaciers in the South Island, however very little work has been done in the North Island. Glaciers have a close relationship with both temperature (primarily affecting the amount of melting) and precipitation (which in the form of snowfall, creates and extends a glacier). So by working out where a glacier once existed and how extensive it was you can then investigate the temperature and precipitation drivers for that time.

Developing the picture of past environments and climates is a vital step in understanding causes of climate change and, together with climate simulation models, looking at future change.

The detective work for these glaciers had been largely achieved on numerous previous trips. Glaciers erode valleys into bedrock slopes and deposit large moraine ridges made out of all this eroded boulder material at its limits. The next stage is to provide an age of when these glaciers formed the valleys and deposited the moraines. A best guess would be that they were this extensive during the last ice age (about 20,000 years ago), but science doesn’t make such great assumptions so this needs to be tested.

Tramping around Ruapehu in search of boulders to sample

Using a similar approach on Tongariro and Ruapehu to what I am using for Antarctic glaciers, the ages of when glaciers and ice caps last existed and then retreated can be determined. Put simply, cosmic radiation which has been stored in a boulder’s surface since it was uncovered and deposited by glacier ice, is measured and compared to a known rate of radioactive decay and therefore an estimation of its time since exposure can be calculated. Many days tramping around these mountains and copious boulders later, we had an ample collection of samples. Stay tuned, the dates are probably a year or two away.

So basically, all this (one-way) chat is just to introduce my first attempt of time lapses and video editing. It will also hopefully explain why we are using a circular saw to attack rocks. It’s in the name of Science.


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