A series of small earthquakes have been recorded under Mt Ruapehu in the past week, but the volcano remains at a low level of unrest, according to GNS Science.
The agency issued a volcanic activity bulletin earlier today. Mt Ruapheu's volcanic alert level remains at level one, the lowest level, and the aviation colour code remains green.
Last week, 40 small earthquakes ranging in size from magnitude 0.3 to 1.8 were located between 3-6km beneath the volcano, with most in the 4-5 km range, GNS Science said.
"Very similar earthquake activity was observed at the beginning of 2022."
Ruaphe's Crater Lake, Te Wai ā-moe, has been slowly heating since mid-October, currently reaching 19C, but overall volcanic activity remains low.
"Past history shows that the lake temperature drops temporarily due to short-lived input of snow melt and heavy rainfall into the lake," the duty volcanologist said.
"These short-term variations do not affect the long-term heating or cooling trends. The heat flow into the lake is currently low at around 80 megawatts, typical of a cooler lake.
"An observation flight on November 22 noted the lake colour had changed to a blue green from the more common grey colour seen in the last few months.
"No upwellings were observed, although sulphur slicks were seen on the lake surface and the lake was overflowing."
Volcanic tremor, a key indicator of volcanic fluid movement, remains low and most other monitoring indicators are within normal ranges, according to the duty volcanologist.
Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of minor volcanic unrest.
Volcanic alert level one indicates the primary hazards are those expected during volcanic unrest: steam discharge, volcanic gas, earthquakes, landslides, and hydrothermal activity.
Authorities caution that the volcanic alert level reflects the current level of unrest and should not be used to forecast future activity.
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