Volcanic tremor at Ruapehu volcano among the highest levels since 2013, New Zealand

Mount Ruapehu Crater Lake

The volcanic tremor at New Zealand’s Ruapehu volcano is now among the highest levels seen over the past 9 years. The Volcanic Alert Level remains at Level 2 and the Aviation Colour Code at Yellow.

Over the past eight days, the temperature at Ruapehu’s Crater Lake (Te Wai ā-moe) has risen further from ~32 °C (89.6 °F) to ~36 °C (96.8 °F), GNS Duty Volcanologist Yanik Behr noted.1

“Our modeling suggests that the temperature rise corresponds to about ~460 MW of heat entering the lake. Temperature and heat input are within the typical range for a heating cycle.”

Volcanic tremor levels remain elevated and, after a slight increase over the past week, are now amongst the highest levels we have seen over the past nine years.

Mount Ruapehu Crater Lake
Mount Ruapehu Crater Lake. Credit: GNS

Crater Lake water and gas sampling and an airborne gas flight were completed last week.

“Analysis of the lake water and gas samples do not indicate significant changes in the geothermal system feeding into the lake,” Behr said, adding that the amount of gas released through the lake has increased from the previous measurements but remains within the typically observed long term trends.

The crater lake has changed to a battleship grey color as upwelling waters have disturbed sediments on the lake floor. Sulfur slicks are present on the lake surface.

The results to date are typical for the beginning of a heating cycle with the exception that tremor values are unusually high.

Current data indicate that normal processes seen at the crater lake are occurring.

Gas and fluids from the shallow magma under the volcano are interacting with the crater lake geothermal system, causing heating of the lake, volcanic tremor, and increases in gas emission at the surface.

The interpretation of this activity is consistent with elevated volcanic unrest and therefore the Volcanic Alert Level remains at Level 2. The Aviation Color Code remains at Yellow.

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

The Volcanic Alert Level reflects the current level of elevated volcanic unrest. The Volcanic Alert Level should not be used to forecast future activity. However, at Volcanic Alert Level 2, eruptions are usually more likely than at Volcanic Alert Level 1.

Volcanic Alert Level 2 indicates the primary hazards are those expected during volcanic unrest; steam discharge, volcanic gas, earthquakes, landslides and hydrothermal activity. While Volcano Alert Level 2 is mostly associated with volcanic unrest hazards, eruptions can still occur with little or no warning.

Geological summary

Ruapehu, one of New Zealand’s most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200 000 years ago.

The 110 km3 (26.4 mi3) dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 (24 mi3) ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank.

A series of subplinian eruptions took place between about 22 600 and 10 000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene.

Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3 000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.2


1 Mt Ruapehu volcanic tremor and Crater Lake heating continues. Volcanic Alert Level remains at Level 2 – GeoNet – April 5, 2022

2 Ruapehu – Geological summary – GVP

Featured image: Mount Ruapehu on March 31, 2022. Credit: Copernicus EU/Sentinel-2, TW

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