Mt Ruapehu’s volcanic alert level has been raised to Level 2 amid an “elevated volcanic unrest”, according to GeoNet.
"While Volcano Alert Level 2 is mostly associated with volcanic unrest hazards, eruptions can still occur with little or no warning," GeoNet volcanologist Craig Miller wrote in a volcanic activity bulletin.
Hazards associated with volcanic unrest include steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity.
It follows the beginning of a new heating phase at Mount Ruapehu and Crater Lake which saw temperatures rise to 31°C.
The rise in temperature is accompanied by “strong levels of volcanic tremor”, also known as volcanic earthquakes.
"There’s an increased likelihood of eruptive activity as strong tremor is indicating increased gas flux through the system," Miller said.
"Despite an increase in gas flow, the lake temperature is only responding slowly, suggesting a partial blockage may exist in the vent beneath the lake. This could allow pressure to build up within the volcano.
"The interpretation of this activity is consistent with elevated volcanic unrest and therefore we have raised the Volcanic Alert Level to Level 2."
Lake temperatures in the active stratovolcano, located south of Taupō’s Volcanic Zone, peaked at 32°C in January 2022, before lowering to around 27-28°C in late February.
The lake temperature has since risen to 31°C from March 13.
"As sometimes occurs during these heating phases, volcanic tremor activity has been recorded," Miller said.
Miller said while the lake is "currently overflowing into the Whangaehu river", the flow level "is believed to be minor".
However, he noted that the lake’s colour is expected to become a "darker grey colour as sediments on the lake floor are disturbed during the influx of hot fluids heating the lake".
The Aviation Colour Code remains at Green.
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