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Volcanic tremors continue on Mt Ruapehu, alert level unchanged

crater lake
Photo from RNZ

News from GeoNet
The temperature of the crater lake (Te Wai ā-moe) at Mt Ruapehu has decreased from 43 to 41 °C during the past week. 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, 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.

Report from RNZ – December 22
A 2km exclusion zone has been established around the peak on Mt Ruapehu, after the volcanic alert level was raised yesterday. This means the crater lake, Te Wai ā-moe, is no longer accessible for guided walks.

Stewart Barclay, director of Adrift Tongariro Guided Adventures, took a group up to the crater lake just two days ago.

“The lake was looking pretty grey when we were up there,” he said. “I remember what [volcanologist] Dr Harry Keys, who I talk to quite a bit, was saying, when it’s grey, it means the vents are opening up a wee bit. I was up again on Wednesday prior, and it was pretty grey then. It’s generally quite a lovely milky blue.”

He’d noticed some other activity a bit earlier in the season.

“Not so many weeks ago there was quite a good steam puff that we videoed as it kind of came off the lake and then went westwards. We kind of thought that was definitely a minor increase in activity. So we made sure we turned around and got out of there quick smart.”

The volcanic alert bulletin for Ruapehu was issued just after midday yesterday, as the temperature of Te Wai ā-moe hit 43C. Such heights aren’t uncommon, but GeoNet said what caused the escalation of alert level were the accompanying bursts of volcanic tremor, and the marked increase in the amount of gas passing through the lake.

Adrift Tongariro was called yesterday morning and given the news. Barclay said it was hard to take, after a year which has hit tourism operators particularly hard anyway.

“So our summer’s down to about ten percent of what it was, and this is just another little kick in the guts. We’ve taken the attitude that for the next 12 months we’ll just ride whatever gets chucked our way, and this is just another little stone thrown at us.”

The High Noon Express ski-lift – part of Ruapehu Alpine Lifts’ Turoa skifield – is within the 2km no-go zone. Chief operating officer Travis Donoghue said that ski-lift wasn’t open during the summer months and so their normal service was carrying on.

“The Sky Waka gondola for us, and subsequent sightseeing, at this stage is not affected. What we do though, of course, is continue to respond to any recommendations and protocols from any agency in respect to any activity at Mt Ruapehu.

“If there was a further escalation of alert levels, that could potentially have an impact on operations. But we work with the relevant agencies advice around any changes and the timely communications on those means everything’s achieved in a timely way.”

Volcanologist at the University of Auckland, Professor Shane Cronin, told Morning Report the 2km buffer zone is a great idea.

“We get a bit of a false sense of security with this volcano so Te Wai ā-moe looks peaceful and calm, the top part of Ruapehu is covered by the deep lake and so if that lake wasn’t there, what we would see would be something like Whakaari, it would be lots of steaming … some liquid suflur, we would see lots of boiling and so on.”

Cronin said he’s concerned going from level 2 to level 3 requires an eruption and there needs to be another step in the system to indicate an eruption is more imminent.

The last time Mt Ruapehu’s alert was raised to level 2 was four years ago and it stayed there for four months. When Whakaari / White Island erupted last year, it was also at level 2.

Ruapehu District Council mayor Don Cameron said everyone was aware of what could happen.

“I wouldn’t say it’s a level of concern yet, but we are at a heightened level of making sure that everybody is aware there could be a further heightening of unrest, and that people need to be aware of it, so that, if for instance, there are people up on the mountain, they can get them down and out really quickly and safely.”

Wellington.Scoop – December 21
The volcanic alert level for Mt Ruapehu has today been raised to Level 2.

News release from GeoNet
The Ruapehu Crater Lake (Te Wai ā-moe) continues heating and is now 43 °C. The heating has been accompanied by bursts of volcanic tremor and a marked increase in the amount of gas passing through the crater lake. The volcanic alert level has been raised to Level 2 and the Aviation Colour code changed to Yellow.

The Crater Lake (Te Wai ā-moe) temperature has been rising and is now 43ºC. During a gas flight last week, the lake was observed to be a uniform grey colour which shows it is well-mixed. There is some flow over the outlet. The gas output through the crater lake has also increased markedly in response to this heating cycle.

The amounts of carbon dioxide (CO2) and sulphur gases (SO2 and H2S) in the plume are the largest measured in the past two decades. The continued flow of gases and hydrothermal fluids though the lake shows that the underlying vent area is open.

Volcanic tremor is being produced as short-lived pulses that coincide with increased gas passing through the crater lake and its plumbing system. Modelling of energy input into the lake has shown increase during the past month from around 200 MW to around 400 MW. Since 2007 Crater Lake temperature has exceeded 40 °C a number of times, without leading to an eruption. However. the combination of the increased lake temperature, volcanic tremor and gas output have motivated the Alert Level change.

The Volcanic Alert Level has been raised to Level 2. The Volcanic Alert Level 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 is changed to Yellow.

The Volcanic Alert Level reflects the current level of volcanic unrest or activity and is not a forecast of future activity. 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 environmental hazards, eruptions can still occur with little or no warning.

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