Typically, over periods of months, Ruapehu’s crater lake (Te Wai ā-moe) experiences heating and cooling cycles. In late December 2020 the lake heated to around 43°C marking the high point of the previous cycle. Early 2021 the lake cooled through to February 2021, before starting to heat again in early March. A maximum of 41°C was reached on 12 April 2021. The lake then started to cool down to 20°C on 2 July. The lake temperature started to rise again last week and is currently 23°C.
While the lake was cooling (April-July) the modelled heat input into the lake was around 80-100 MW (megawatt). To heat the lake water temperature by 3°C modelling indicates that ~300-600 MW (megawatt) of heat is now entering the lake.
Two small earthquakes have been located, and higher level of volcanic tremor has accompanied the start of the increase in the lake temperature. The occurrence of tremor is quite typical of the start of such heating phase.
Routine monitoring at the volcano includes gas measurement flights and crater lake (Te Wai ā-moe) water samplings. The results from these visits and of continuous monitoring of volcanic earthquake activity, tremor levels, and crater lake (Te Wai ā-moe) temperature and water level indicate that key monitoring parameters remain within normal ranges. The lake is currently overflowing into the Whangaehu river.
The Volcanic Alert Level remains at Level 1 and the Aviation Colour Code remains at Green.
Source: GeoNet New Zealand volcano activity update 16 July 2021