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Researchers aim to measure mountain growth rate - 26/01/2000

Researchers from New Zealand and the United States are using highly accurate global positioning system (GPS) equipment to measure how fast the Southern Alps are growing in height.

The five-year project, which gets underway this weekend, is aimed at understanding how mountains grow and how the Earth’s crust is deforming under the Alps, which mark the boundary of the Australian and Pacific tectonic plates.

Involved are researchers from the Institute of Geological & Nuclear Sciences Limited (GNS), Otago University, the Massachusetts Institute of Technology, and the University of Colorado.

It will be the first time anywhere in the world that researchers have attempted to systematically measure the present-day uplift rate across a major mountain range.

The uplift rate of the Southern Alps, deduced through geological methods, is thought to be as high as 10mm-a-year. Researchers want to put that estimate to the test and to find out the variation in uplift rates from one side of the mountain range to the other.

" Over the past five million years, tectonic forces have pushed the Southern Alps up by as much as 25 kilometres," said GNS geophysicist John Beavan.

" It’s only the fast pace of erosion that has kept their highest point – Mt Cook – below 4000m," Dr Beavan said. (In January 1992 a section of Mt Cook’s summit broke off, reducing the mountain’s height by 20m).

Over the next two weeks the researchers will install four permanent GPS receivers atop rocky Southern Alps peaks that are not vulnerable to erosion. They will be working near the Copland Valley, in the Mt Cook region. The solar-powered receivers will be able to detect height changes as small as 1mm-a-year.
The instruments will take readings every 30 seconds and send the data via radio and the internet to Wellington for analysis.

" We don’t expect to find anything straight away – we’re interested in the long-term trend. New Zealand’s geological processes are fast by world standards, but it will still take several years of continuous measuring to produce a meaningful result."

The equipment has been supplied by the two American organisations and the New Zealand and American researchers will collaborate in analysing the data.

One piece of equipment being brought from the United States is an absolute gravity meter which will be used to detect minute changes in gravity under the Southern Alps during the next five years. There are only a few such instruments in the world and none in New Zealand.

A small decrease in gravity is expected because in five years (and barring landslides like the 1992 rockfall on Mt Cook) the summits of the Alps will be about 50mm further from the centre of the earth. This small increase in height will result in a small and measurable decrease in gravity.