Brief period of strong volcanic tremor under Ruapehu, New Zealand

ruapehu on june 19 2022

A brief period of strong volcanic tremor was recorded over the weekend at Ruapehu volcano, New Zealand. The Volcanic Alert Level remains at Level 2. An eruption at the volcano may occur at any level, and levels may not move in sequence as activity can change rapidly.

For about three weeks, tremor levels had been weak-to-moderate but on Friday evening (local time/LT), June 17, 2022, volcanic tremor increased sharply and fluctuated between moderate and strong levels over the weekend, GNS Duty Volcanologist Geoff Kilgour noted.1 On Sunday, June 19, volcanic tremor returned to weak levels.

Crater Lake (Te Wai ā-moe) temperature had been decreasing at a rate of ~ 0.5 °C (0.9 °F) per day until it stabilized over the weekend and is now 22 °C (71.6 °F). This is consistent with an increase in heat flow into the lake to approximately 130 MW.

The return of moderate-to-strong volcanic tremor and stabilization of Crater Lake temperature are consistent with a continued period of moderate volcanic unrest at Mt Ruapehu, Kilgour said.

“We will carry out a gas measurement flight and Crater Lake sampling when the weather allows. As noted last week, the level of unrest is now considered moderate rather than heightened, however, the potential for eruptive activity remains.”

Within the next three weeks, the most likely outcome of the ongoing unrest is no eruption. Minor eruptive activity, confined to the lake basin, is also possible, which could generate lahars (volcanic mudflows) in the Whangaehu River.

The next likely scenario is an eruption that impacts the summit plateau with volcanic surges. That event could generate lahars in multiple catchments, like what was seen after the September 2007 eruption. An eruption of this size would cause life-threatening hazards on the summit plateau and in valleys impacted by lahars.

The chance of a prolonged eruptive episode or a larger eruption, with wider ashfall impacts such as occurred in 1995-96, is higher than it was before the start of elevated unrest in March 2022, but within the next three weeks, this scenario remains very unlikely. Such an eruption would most likely only follow a sequence of smaller eruptions.

The increased tremor over the weekend highlights the variability and significant uncertainty about the state of the volcanic process that has been driving the current unrest period.

“Our interpretation of the observational data and activity is, therefore, still consistent with moderate volcanic unrest and therefore the Volcanic Alert Level remains at Level 2. The Aviation Colour Code remains at Yellow.”

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

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

References:

1 Short period of increased volcanic tremor over the weekend at Mt Ruapehu. The Volcanic Alert Level remains at Level 2 – GeoNet – June 20, 2022

2 Ruapehu – Geological summary – GVP

Featured image: Ruapehu on June 19, 2022. Credit: Copernicus EU/Sentinel-2, EO Browser, The Watchers

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