Mt Ruapehu shows signs of 'elevated unrest'

22:16, Apr 05 2011
Mt Ruapehu's crater lake
Mt Ruapehu's crater lake is going through a hot phase much longer than the norm.
Graph of heating at Ruapehu's crater lake
Graph shows changes in temperature at Ruapehu's crater lake.

Temperatures at Mt Ruapehu's Crater Lake are on the rise, with vulcanologists issuing an alert for pilots flying over the mountain.

GNS Science said today that high water temperatures, currently about 38 - 39C, were being experienced in the lake.

GeoNet duty vulcanologist Agnes Mazot said changes had also recently occurred in volcanic gas output, seismic activity and Crater Lake water chemistry.

"These changes show that Ruapehu is experiencing signs of elevated unrest above known background levels," she said.

Despite the changes, Mazot said there were currently no indications an eruption was imminent.

The volcanic alert level remained at level one, which meant there were signs of volcanic unrest.

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However, the Aviation Alert Code had been raised to yellow to let pilots know about the change in activity on the mountain.

The four-tiered volcano alert level used the terms normal, advisory, watch, and warning, with yellow being the advisory category.

Mazot said the lake reached its highest recent temperature of 41C on March 1.

The temperature of Crater Lake was a measure of the amount of volcanic heat coming from Ruapehu.

"Since the lake was re-established in 2002, the highest recorded temperature was 42.5C in May 2003, and there have been eight heating cycles," Mazot said.

Changes which had taken place recently in lake chemistry, increases in carbon dioxide gas emissions and minor increases in seismic activity beneath the volcano "have not been observed during previous periods of high lake temperature," Mazot said.

They indicated that Ruapehu was experiencing a period of unrest above that which was typical.

While there were currently no indications an eruption was imminent, Ruapehu remained an active volcano and future eruptions could occur with little or no warning, she said.

Ruapehu last erupted in 2007, producing two lahars, a column of ash and a rock fall.

Primary school teacher William Pike, who was camped at the Dome Shelter near the crater, was crushed by a rock thrown up in the eruption.

His right leg had to be amputated so he could get down from the mountain.

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