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Getting the measure of the volcano - 23/12/2009

When it comes to tough environments, Mt Ruapehu's Crater Lake is harsher than most. Temperatures get down to minus 10 degrees Celsius in winter and the water in the Crater Lake is about pH1, or similar to battery acid.

GNS Science technician Jeremy Cole-Baker checks electronic measuring equipment at the edge of Ruapehu's Crater Lake. Photo: GNS Science

GNS Science technician Jeremy Cole-Baker checks electronic measuring equipment at the edge of Ruapehu's Crater Lake. Photo: GNS Science

Installing automated measuring systems at Ruapehu’s summit has been a challenge for scientists since the 1960s. Most of the equipment has succumbed to the cold at 2550m altitude and the corrosive lake environment.

The temperature of the lake tells scientists how much heat energy the volcano is producing - a good indicator of its level of volcanic activity.

This year scientists succeeded in getting an automated measuring system working right through winter, taking hourly readings of the lake temperature without skipping a beat.

Typically volcanologists from GNS Science take a helicopter to the summit once a month and dip instruments into the lake to get their readings. But 12 temperature measurements a year gives only a partial view of Ruapehu’s ever-changing volcanic system.

Hourly measurements provide a much more precise picture of the volcano's moods and will empower scientists in their quest to understand the complex volcanic plumbing beneath the Crater Lake.

The automated measuring is thanks to a combination of improved electronic gear and sturdy weather-proof plastic tool boxes obtained at a hardware store. The electronic gear draws only a small amount of electricity, which is provided by vehicle batteries. Data is transmitted from the summit by satellite to data centres in Wellington and Taupo.

The equipment was installed in the autumn of 2009 at the edge of the Crater Lake, with the permission of the Department of Conservation and in consultation with iwi groups.

GNS Science technician Jeremy Cole-Baker checks the condition of electronic probes in Ruapehu's Crater Lake. The equipment sits about 6m out in the lak and is weighed down by a 'holland paver'  which gradually dissolves in the acid environment and needs to be replaced at least once a year. Photo: GNS Science

GNS Science technician Jeremy Cole-Baker checks the condition of electronic probes in Ruapehu's Crater Lake. The equipment sits about 6m out in the lak and is weighed down by a 'holland paver' which gradually dissolves in the acid environment and needs to be replaced at least once a year. Photo: GNS Science

Technician Jeremy Cole-Baker and volcanologist Tony Hurst, both of GNS Science, dug the two large plastic boxes containing the electronic equipment and batteries in to the volcanic rubble beside the lake.

The boxes became covered in about 2m of snow in May and emerged into the sunlight with the spring thaw in December. The temperature inside the boxes hovered at zero degrees right through winter.

Dr Hurst says scientists are encouraged by the steady stream of data coming from the summit as it will help in understanding Ruapehu’s volcanic system.

“This summer we will add a hydrophone to the instrument cluster in the lake to record episodes of steam and gas bubbling into the lake from the deep vents at the bottom of the Crater Lake.”

This will tell scientists if gas bubbling occurs before or during warming of the lake, a key element in fathoming the way Ruapehu works.

Several hundred megawatts of heat energy go into the crater lake, Dr Hurst says.

“It’s comparable to the output of a moderate-sized geothermal power station.”

The temperature of the six million cubic metres of water in the Crater Lake cycles sporadically between 19degC and 55degC. The mountain always keeps scientists guessing how much the lake temperature will change and when it will change.

Crater Lake measurements are supported by a brace of other monitoring equipment around the mountain designed to detect the early signs of volcanic unrest.

This includes seismographs to detect volcanic earthquakes and GPS instruments measuring ground deformation. As magma fills a volcano’s eruptive chamber, its sides can swell by many centimetres indicating that eruptive activity may be imminent.

Any one measurement taken in isolation could give a misleading view of the volcano. The pooling of multiple measurements from different parts of the volcano gives a more complete picture, Dr Hurst says.