Published: Wed Jun 6 2018 9:30 AM
Te Wai ā-moe (Crater Lake) temperature at Mt Ruapehu is rising along with an increase in volcanic tremor. This is consistent with minor volcanic unrest behaviour. The Volcanic Alert Level remains at 1.
Te Wai ā-moe has a clear temperature cycle that we have observed since 2003. During these cycles, the temperature ranges between ~12 and 40 °C over a period of ~12 months. In our last report (RUA 2018-02), we described how the relatively long-period of elevated temperature of Te Wai ā-moe was coming to an end. During that elevated temperature period, the lake reached ~ 38°C and we expected the lake to then cool as it has done many times before. Over the past 2 months, the lake has indeed cooled to ~ 20 °C where it remained at this low temperature until Tuesday last week, when the lake starting heating again at a rate of ~ 1 °C per day. Following previous heating cycles, we expect the lake to continue heating for the coming weeks.
Coincident with the increasing lake temperature, we have also noticed that the level of volcanic tremor has increased. This is a characteristic feature of a heating cycle and represents the increased flow of hydrothermal fluids into the lake. Previous heating cycles have shown this increased tremor to last for days to weeks.
As part of our normal routine monitoring, we aim to visit Te Wai ā-moe this week (weather permitting) to collect water and gas samples from the lake.
The Crater Lake has undergone many heating and cooling cycles in the past and we don’t see any unusual signs of increased unrest. Therefore, current observations are consistent with minor unrest behaviour and because of this, we remain at Volcanic Alert Level 1 and the Aviation Colour Code stays at Green.
Volcano Alert Level 1 corresponds to minor unrest. While this is the case, it is a useful reminder that eruptions can occur with little or no warning. GNS Science continues to closely monitor Mt Ruapehu and our other active volcanoes.
Geoff Kilgour Duty Volcanologist