Mt Ruapehu Crater Lake temperature down to 41 ̊C but volcanic tremor still elevated

Published: Mon Dec 28 2020 1:00 PM

Volcanic Alert BulletinRUA –2020/11
Mon Dec 28 2020 1:00 PM; Ruapehu Volcano
Volcanic Alert Level remains at 2
Aviation Colour Code remains at Yellow

During the past week, the temperature of the crater lake (Te Wai ā-moe) at Mt Ruapehu has decreased from 43 to 41 °C. The level of volcanic tremor continues to be moderate to strong and a small number of shallow volcanic earthquakes have been recorded. While the crater lake may have stopped heating, volcanic activity at Mt Ruapehu remains elevated. The Volcanic Alert Level remains at Level 2 and the Aviation Colour Code remains at Yellow.

Since our last update (VAB RUA - 2020/10), Ruapehu’s Crater Lake (Te Wai ā-moe) temperature has decreased slightly. The temperature reached a maximum of 43 ºC on Monday 21st December that subsequently declined to ~41 ºC. A lake temperature peak of ~ 40-46 ºC is common during these heating-cooling cycles; on at least 7 occasions since 2007, the lake temperature exceeded 40 ºC. Using this lake temperature decrease, we estimate that the energy input into the lake has decreased from ~400 to ~200 MW (megawatt).

Elevated volcanic tremor is still ongoing along with a few volcanic earthquakes. The largest of these earthquakes (M2.2) occurred on 26th December and was located under the volcano. Volcanic earthquakes of this size are uncommon and the combination with elevated tremor and still high lake temperature indicate moderate to heightened volcanic unrest. Because of this, the Volcanic Alert Level remains at Level 2.

We continue to closely monitor Ruapehu, and this week we will attempt a gas flight to measure volcanic gas emissions. We will also attempt to sample the water at the crater lake for further chemical analyses. Together, these will help us identify processes occurring at depth beneath the volcano.

The Volcanic Alert Level is still at Level 2 which reflects the current level of volcanic activity. 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 at Yellow.

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

Volcanic Alert Level 2 indicates the primary hazards are those expected during volcanic unrest: steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity. While Volcanic Alert Level 2 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 website or follow DOC’s Facebook page for further updates.

GNS Science and the National Geohazards Monitoring Centre continue to closely monitor Mt Ruapehu for further changes in unrest. GeoNet monitors Mt Ruapehu via a network of seismic and acoustic sensors, GNSS (GPS) receivers, sensors in the lake and visits to the lake area and gas flights.

Agnes Mazot Duty Volcanologist

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