Mt Ruapehu status update: Crater Lake (Te Wai ā-moe) now cooling

Published: Tue Sep 28 2021 9:30 AM

Volcanic Alert BulletinRUA – 2021/05
Tue Sep 28 2021 9:30 AM; Ruapehu Volcano
Volcanic Alert Level remains at 1
Aviation Colour Code remains at Green

Another heating phase has passed at Mt Ruapehu. Over the last two months the temperature of Crater Lake (Te Wai ā-moe) rose from 20 °C to 39.5 °C, peaking on 4 September 2021, and has now cooled to 28 °C. The Volcanic Alert Level at Mt Ruapehu remains at Level 1.

Typically, over periods of months, Ruapehu’s Crater Lake (Te Wai ā-moe) undergoes heating and cooling cycles.

In late December 2020 the lake heated to 43 °C marking the high point of that cycle. Later in April of 2021 a 2nd cycle reached a maximum of 41 °C. The latest cycle is the third this year and the heating phase lasted from early July to early September 2021, during which the temperature rose from 20 °C to 39 °C.

The temperature of Ruapehu Crater Lake (Te Wai ā-moe) is now cooling

The temperature of Ruapehu Crater Lake (Te Wai ā-moe) is now cooling

During the heating cycle the lake colour changed to a darker grey, from a blue-green colour. This is typical as sediments on the lake floor are disturbed during the influx of hot fluids and are suspended in the lake water.

The modelled heat flow into the lake has now dropped from 350-400 MW at the peak of the heating to around 200 MW (megawatt).

The lake is currently not overflowing into the Whangaehu river.

Routine monitoring at Mt Ruapehu includes gas measurement flights and Crater Lake (Te Wai ā-moe) water sampling.

The results from these visits and of our continuous monitoring of volcanic earthquake activity, tremor levels, and lake temperature and water level indicate that key monitoring parameters remain within normal ranges.

The Volcanic Alert Level stays at Level 1 which reflects the current level of volcanic unrest. The Volcanic Alert Level should not be used to forecast future activity.

The Aviation Colour Code remains at colour Green.

Mt Ruapehu is an active volcano and has the potential to erupt with little or no warning when in a state of volcanic unrest.

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.

GNS Science and the National Geohazards Monitoring Centre continue to closely monitor Mt Ruapehu for further changes.

Craig Miller

Duty Volcanologist

Media Contact: 021 574 541 or