All eyes on rumbling Ruapehu as volcanic activity continues
A mayor has described locals as ‘‘ready for anything’’ as volcanic unrest at Mt Ruapehu during the past four weeks marked ‘‘the longest period of tremor recorded over the past 20 years’’.
GeoNet said the elevated volcanic unrest was continuing, ‘‘with strong volcanic tremor and the Crater Lake temperature now stabilised at 37C for the past week’’. The volcanic Alert Level remains at level 2.
Ruapehu Mayor Don Cameron said at this stage residents were aware but not worried. ‘‘It is not a real concern, we do know Ruapehu heats up for extended periods of time every five years or so,’’ Cameron said.
‘‘Local people are used to seeing this type of information coming out.’’
He said they were ‘‘certainly ready for anything that does happen’’.
‘‘We don’t feel there’s any danger at this stage,’’ he said, noting GeoNet was not suggesting it expected an eruption.
He also said the area was busy with visitors, a view supported by Ruapehu Mountain Motel & Lodge co-owner Leigh Berry. ‘‘As a local, we’re not worried, but the guests do talk about it,’’ Berry said.
Rhere were currently a lot of Aucklanders in the area who ‘‘haven’t skied for the last two years, people are really keen to ski and board,’’ Berry said.
She said that after the Covid restrictions the area needed a good season: ‘‘We’re just hanging in there after Covid.’’
GeoNet volcanologist Agnes Mazot said the heightened unrest was primarily manifested as volcanic tremor and heat flow into the summit crater lake. ‘‘The tremor levels remain elevated, representing the longest period of tremor recorded over the past 20 years,’’ Mazot said.
‘‘An observation flight and sampling of the crater lake were performed last week ... scientists observed some upwelling in the lake, indicating that hot gas and liquid are still making their way into the lake.
‘‘The crater lake remains a battleship grey colour with upwellings only at the northern vents area and no overflow. Sulphur slicks are also present on the lake surface. All these characteristics are usual for Ruapehu crater lake during a heating phase.’’
Mazot also said that during the past 30 days the temperature of the crater lake increased by 7C and while this was like previous heating phases, the heating had slowed and the temperatures had been steady around 37C for the past week.
‘‘This slowing of the heating, in spite of the ongoing strong level of volcanic tremor continues to indicate heightened volcanic unrest as pressure could be building up at depth.’’
Mazot said the sustained nature of the volcanic unrest, coupled with the volcanic tremor signals, elevated gas output and hot lake remain indicative of processes being driven by molten rock (magma) interacting with the geothermal system within the volcano.
‘‘The order of the potential outcomes has not changed since last week. The most likely outcome of this unrest episode within the next four weeks is still that no eruptive activity occurs, as no eruptions have followed unrest in the past 15 years.
‘‘However, there is also a possibility of a single or multiple eruptions that could impact the summit area and generate lahars into some catchments draining off the volcano, especially the Whangaehu Valley.
‘‘The size of these eruptions, if they did occur, would probably be like that of September 2007, or the slightly larger April 1975 or June 1969 events.’’
The chance of a prolonged and larger eruption, such as occurred in 1995-96 with wider ashfall impacts, was higher than two months ago, but remained very unlikely. Such an eruption would most likely only follow a sequence of smaller eruptions, she said. The interpretation of this activity is consistent with elevated volcanic unrest at the heightened level and therefore the Volcanic Alert Level remains at level 2. The Aviation Colour 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.
‘‘As a local we’re not worried, but the guests do talk about it. ’’
Leigh Berry
Ruapehu Mountain Motel & Lodge co-owner