Te Wai ā-moe (Ruapehu Crater Lake) remains cool, with the current daily mean temperature around 8ºC, marking a 3ºC drop since late August. This is the lowest recorded temperature since 1970, with a previous low of 9ºC measured in 1988. The lake’s temperature typically fluctuates in response to volcanic heat input, but since mid-February, there has been minimal heat influx, causing the ongoing cooling.
Historically, eruptions at Ruapehu are more frequent when the lake is warmer than average, though there is also a slightly increased chance of eruption during cooler periods.
The reduced heat flow into the lake suggests that mineral deposits may be sealing vent areas. While sulfur dioxide (SO₂) emissions through the lake have also decreased in 2024, the continued detection of volcanic gases indicates that the vent is not completely sealed. This is supported by observations from September 30, when upwellings and sulphur slicks were seen on the lake surface.
The cooling of Te Wai ā-moe, along with reduced SO₂ emissions, aligns with the cooling of the hydrothermal system beneath the lake. Volcanic tremor levels, typically associated with fluid and gas movement in the hydrothermal system, have remained low throughout the year, with no changes detected in other monitored parameters.
Despite these indicators, an unexpected eruption could still occur if a sudden buildup of gas beneath the partly sealed vent releases pressure. Recent observations suggest ongoing low-level volcanic unrest at Ruapehu, with low lake temperatures and gas emissions signaling partial sealing of the vent system. However, the likelihood of an eruption remains low.
Thus, The Volcanic Alert Level remains at 1 and the Aviation Colour Code at Green.
Source: GNS Science/GeoNet New Zealand volcano activity update 8 October 2024