Mt Ruapehu volcanic unrest level lowered - sudden eruption risk remains

Volcanic unrest at Mount Ruapehu 's Crater Lake continues to decrease, with the alert level lowered. Photo / GNS

Volcanic unrest at Mount Ruapehu continues to decrease, with the alert level lowered, but the potential risk of a sudden eruption remains.

GNS Science's duty volcanologist Agnes Mazot said the latest Crater Lake chemistry data showed low volcanic tremor levels and a stable warm lake temperature.

As a consequence of the decline in the level of unrest, the volcanic alert level had been lowered to one and the aviation colour code changed to green, she said.

Mazot said analyses of water samples from Crater Lake (Te Wai ā-moe) have now confirmed there has been little recent chemical interaction between magma (new molten rock) and the hydrothermal system controlling the composition, level, and the temperature of the Crater Lake.

She said Te Wai ā-moe's temperature decreased from a high of 40C in early May to 21C on June 14, and in the following two weeks recovered to 25C.

"The temperature has stabilised or fallen slightly this last week was currently at 24C consistent with heat flow into the lake of about 100MW.

"The period of strong volcanic tremor, from mid-March to early-June 2022 has declined to near background levels and generally lower gas emission rates are being recorded.

"Short-lived pulses of gas are still reaching the surface. When taken together these observations are consistent with a decline in volcanic unrest at Mt Ruapehu."

Mazot said over the last week, volcanic tremor has remained weak and it had been more than 20 days since the last higher tremor levels.

However, she said Mount Ruapehu had the potential to erupt with little or no warning when in a state of minor volcanic unrest.

"Over the last two to three months a magmatic intrusion has occurred inside the volcano, increasing heat and gas flow into the hydrothermal system associated with the Crater Lake. Our data indicate that the intrusion has stalled or stopped moving."

Recently stalled magma in the volcano suggests that a sudden resumption of activity would be more possible than the last time Ruapehu was at volcanic alert level 1, she said.