Mt Ruapehu certainly active as crater temperature and volcanic tremor rise
07/09/2016
Mt Ruapehu's crater lake has heated significantly in the past five days.
A rapidly heating crater lake shows that Mt Ruapehu is certainly not dormant.
Sharp increases in the temperature of the crater lake, in Tongariro National Park, and an increase in volcanic tremors have been recorded by GeoNet.
The temperature of the crater lake has risen to 17.6 degrees Celsius, from the lowest recorded temperature of 12C on 15 August.
Slowly rising throughout August, the lake has heated significantly in the past five days.
There has also been a marked increase in volcanic tremors, which has not reduced since 4 September.
Duty volcanologist Michael Rosenberg said the temperature change was similar to what they had seen at the end of 2014.
"It's certainly not a regular cycle but we typically see temperatures getting up to 40 degrees
"The tremor has started again, and again we often see that at the same sort of time ... the processes are all linked together."
GeoNet was not currently concerned about the tremors, which weren't "unusually strong".
"What we see now is just part of the normal behaviour of the volcano ... there are no exclusion zones in place at this time.
"Obviously it is an active volcano and it has the potential to erupt at very short notice.
"In a way it's reassuring to see that the normal heating and cooling behaviour is continuing."
The Volcanic Alert Level (VAL) was raised to level 2 in May after the lake reached 46C, the highest recorded temperature since 1999.
This highest temperature was accompanied by volcanic tremors and an increase in volcanic gas.
The VAL was lowered again in early July.
The changes are typical and since 2010 eight such cycles have been recorded.
The highest recorded crater lake temperature was 60C in 1968.
GeoNet constantly monitors the crater lake and the volcano, the largest active volcano in New Zealand and the highest North Island peak, rising to 2797 metres at the southern end of the Taupo volcanic zone.
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