Agnes Mazot

Mt Ruapehu status update: new heating phase starts at the crater lake (Te Wai ā-moe)

Published: Mon Jul 12 2021 3:00 PM
Volcanic Activity Bulletin
Volcanic Activity BulletinRUA – 2021/04
Mon Jul 12 2021 3:00 PM; Ruapehu Volcano
Volcanic Alert Level remains at 1
Aviation Colour Code remains at Green

Another heating phase has started at Mt Ruapehu. Over the last three months the temperature of the crater lake (Te Wai ā-moe) has cooled from 41°C (12 April 2021) to 20°C (2 July 2021). The turnaround of the lake temperature early July has followed two small volcanic earthquakes and has been accompanied by a higher level of volcanic tremor over the weekend, as is often the case at the start of a heating episode. The Volcanic Alert Level at Mt Ruapehu remains at Level 1.

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 our 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 Mt Ruapehu includes gas measurement flights and crater lake (Te Wai ā-moe) water samplings. The results from these visits and of our 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 which reflects the current level of volcanic unrest. Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of volcanic unrest. The Aviation Colour Code remains colour Green.

The Volcanic Alert Level should not be used to forecast future activity, however at Volcanic Alert Level 1, eruptions are less likely than at Volcanic Alert Level 2.

Volcanic Alert Level 1 indicates the primary hazards are those expected during volcanic unrest: steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity. While Volcanic Alert Level 1 is mostly associated with environmental hazards, eruptions can still occur with little or no warning.

For information on access to the Mt Ruapehu area, please visit the Department of Conservation’s websites on volcanic risk in Tongariro National Park and follow their Facebook page for further updates.

Agnes Mazot, Duty Volcanologist Media Contact: 021 574 541 or