Recent data suggests a weak heating trend is underway at Mt Ruapehu’s crater lake after it reached its lowest temperature in 54 years earlier this month.
The risk of eruption at the 2797m stratovolcano remains “low” as the temperature of the lake, known as Te Wai ā-moe, increased from 8C to a daily average of 10-11C — still considered a low temperature.
GNS Science said the Volcanic Alert Level remains at 1 and the Aviation Colour Code remains Green.
Duty volcanologist Mike Rosenburg said the amount of sulphur dioxide (SO₂) and volcanic tremor also declined during this cooling period. This was consistent with the cooling of the hydrothermal system beneath the lake, he added.
“With decreasing upward heat flow, we also expected some mineral sealing to happen beneath the lake, slowing the rate of gases passing through the lake.”
The sub-lake vent likely remained partially sealed although the lake seemed to be heating up again, Rosenburg said.
“Should conditions deep inside the volcano change to produce a significant upflow of gas, it is possible a partly sealed zone below the lake could rupture and produce a small eruption.”
Small eruptions have been observed in heating phases in the past, but Rosenburg said no deep seismic changes have been recorded.
“In the current state of low-level unrest, the likelihood of an unheralded eruption remains low.”
Te Wai ā-moe was expected to slowly heat at the rate of 1C a day in the coming months.
