Increases in crater lake temperature, gas and volcanic tremors have prompted GNS Science to raise the volcanic alert level at Mount Ruapehu.
GNS Science today said the crater lake (Te Wai ā-moe) continued to heat up and was now 43C.
At the same time, the Department of Conservation (DoC )has also mapped out a no go zone around the lake.
DoC said in a statement that as per its volcanic risk management plan, a 2km area surrounding the lake is closed to the public and concessionaires due to increased risk of eruption.
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Mount Tongariro and the Tongariro Alpine Crossing is not affected by increased volcanic unrest at Mount Ruapehu and remains open, it said.
Bursts of volcanic tremor and a marked rise in the amount of gas passing through the lake contributed to the alert level change.
The volcanic alert level had been raised to level 2, reflecting the level of volcanic unrest. The aviation colour code changed to yellow.
"The gas output through the crater lake has increased markedly, with the largest amounts of carbon dioxide and sulphur gases in the plume measured in the past 20 years," GNS Science said.
"This continued flow of gases and heat through the lake shows that the underlying vent area is open. There are volcanic tremors in the form of short-lived pulses, coinciding with increased gas passing through the crater lake and its plumbing system."
Since 2007 the crater lake temperature has exceeded 40C a number of times, without leading to an eruption, however, the combination of the increased lake temperature, volcanic tremor and gas output have motivated the alert level change.
GNS Science and the National Geohazards Monitoring Centre continues to closely monitor Mount Ruapehu for further signs of activity.