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GPS to keep track of Mt Ruapehu's movements - 13/02/1998

New satellite receivers on the side of Mt Ruapehu can measure changes in the shape of the mountain as small as a centimetre and may eventually help in forecasting eruptions, French and New Zealand scientists say.

The global positioning satellite (GPS) receivers have been installed on the flank of the 2797m mountain under a joint scientific accord between New Zealand and France.

The aim of the trial is to track movements of magma deep inside the mountain. GPS monitoring of active volcanoes in the Philippines has shown that movements of magma (hot, molten rock) under the volcano can point to the brewing of an eruption. French scientists have also used GPS technology to monitor alpine landslides in France.

Expansion of the magma chamber under the volcano can deform the mountain by pushing out the sides and making them bulge slightly.

In a joint announcement, Institute of Geological & Nuclear Sciences Limited geophysicist Tony Hurst and Laboratoire d'Instrumentation Geophysique scientist Jean Vandemeulebrouck said they had installed two GPS receivers -- one at Whakapapa and the other 7km up the mountain, 2km from the summit.

They intended to trial the receivers for some months to see how effective they were at detecting small changes in the shape of the volcanic cone.

Until now, the plotting of Mt Ruapehu's land deformation movements had been difficult, Dr Hurst said.

GPS technology, based on a constellation of satellites, had been available for several years, but at huge cost. The Ruapehu system used less expensive receivers and new, clever processing software to analyse the data.

Results should be comparable to using the expensive equipment, Dr Hurst said. The intention was to link the fully automated receivers with the Institute's seismograph network.

By the end of 1988 the receivers would take continuous readings every 15 seconds with the data sent via satellite to Wellington for analysis. It would also be transmitted to France via the Internet so Dr Vandemeulbrouck could work on it simultaneously.

If the trial is successful, more receivers would be installed further up the mountain closer to the crater. Ultimately this technology could be used to help monitor parts of the mountain's crater rim which had been unstable in the past, Dr Hurst said.