As Crater Lake temperatures continue to climb, Mount Ruapehu could erupt on a scale similar to the September 2007 event which injured two climbers in a nearby hut, according to GNS Science.
GNS Science volcanologist Brad Scott said in a volcanic activity bulletin on Tuesday that heightened unrest at the site is primarily manifesting as strong tremors, slowly rising Crater Lake (Te Wai ā-moe) temperatures and increased gas output.
“These changes indicate magma may now be driving the unrest, increasing the chances of further activity,” he said.
Scott said while the tremors “remain elevated”, the levels have declined from its April 6-7 peak.
READ MORE: Ruapehu data to 'clue' scientists into what is driving tremors
Crater Lake’s gas output, meanwhile, on Monday hit its second highest recorded value.
The lake’s temperature is now 38°C, and GeoNet’s modelling suggests around ~280 MW of heat is required to sustain the temperature, Scott said. Mount Ruapehu’s temperature and heat input “remain within the typical range for a heating cycle”.
He said Crater Lake “remains a battleship grey colour" and a "small overflow”, while sulphur slicks are also "present on the lake surface”.
He noted that the “sustained nature of the volcanic unrest now differs from those typically seen during the start of a heating phase”, and the tremors and increased gas output “are now more indicative of processes being driven by molten rock (magma) interacting with the geothermal system at depth in the volcano”.
READ MORE: 'Watch this space' for signs of Ruapehu eruption - geologist
Scott said, however, that in spite of its differences in activity compared to the beginning of other heating phases, “the most likely outcome of this unrest episode is no eruptive activity occurs, as no eruptions have followed unrest in the past 15 years”.
But he noted that there is also a possibility of “a single or multiple eruption 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 the September 2007 event,” he said.
The September 25 incident saw the volcano erupt without warning, injuring two climbers nearby.
“The chances of a prolonged and larger eruption, such as occurred in 1995-96 with wider ashfall impacts, is possible, but remains very unlikely. Such an eruption would most likely only follow a sequence of smaller eruptions.”
Professor Phil Shane says the raising of the volcano's alert level doesn't necessarily mean there will be an eruption. (Source: 1News)
Victoria University of Wellington professor of geophysics, Professor Martha Savage, said Mount Ruapehu “is more active than it has been in about 15 years”.
Savage noted how the Whakaari / White Island volcano was also at Alert Level 2 when it erupted on December 9, 2019.
She said whether it will erupt or not is “difficult to predict”, adding that volcanic eruptions are “somewhat like earthquakes, in that there are many, many more small ones than large ones”.
“The bottom line is, I would not let my children climb up Mt Ruapehu now. It is not hugely likely to erupt soon, but it is much more likely to erupt now than it was two years ago."
READ MORE: Among highest level of Mt Ruapehu volcanic tremors in 9 years - GNS
Scott said the current 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.
Volcanic Alert Level 2 indicates there are primary hazards expected during volcanic unrest, including 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.
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