Mt Ruapehu strong volcanic tremor continues

Mount Ruapehu's crater lake Te Wai a Moe is sitting at 37 degrees – and that requires “a substatial amount of heat”. Photo: Joseph Pearson/Stuff.

Elevated volcanic unrest continues at Mt Ruapehu, dominated by strong volcanic tremor, but experts say an eruption is still unlikely.

Elevated volcanic unrest has now been sustained at Mt Ruapehu for five weeks, says GNS Science duty volcanologist Steven Sherburn.

The Crater Lake (Te Wai ā-moe) temperature remains stable at 37°C.

The Volcanic Alert Level remains at Level 2.

"This heightened volcanic unrest is primarily manifested as volcanic tremor, gas output and heat flow into the summit crater lake," says Steven.

"The volcanic tremor level has varied during the last week but remains elevated overall. This tremor episode now represents the combined longest-strongest period of tremor recorded over the past 20 years."

The Crater Lake (Te Wai ā-moe) temperature has remained around 37 °C (range 36-38 °C) over the past three weeks.

While the temperature has not increased, modelling requires that a substantial amount of heat (about 200-300 MW) is still needed to sustain this high lake temperature, says Steven.

The laboratory analyses of a lake sample collected on April 15 show no changes in Crater Lake water chemistry since March 31.

"The static lake temperature and lack of chemical response indicate processes at shallow depth below the Crater Lake are not being reflected in the lake conditions.

"We did not observe an increase in magnesium concentration that would have pointed at some potential magma-water interaction below the surface.

"We will keep sampling the crater lake regularly to monitor any changes in the water chemistry."

The sustained nature of the volcanic unrest, coupled with the strong 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 at shallow depth (0.5-2 km).

Steven says 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.

"If eruptive activity does follow this unrest, it is expected to be initially small-scale. Such an eruption would impact mostly the summit area, with also lahars further downstream - like the September 2007 eruption or the slightly larger April 1975 or June 1969 events.

"Only if eruptions continued would we expect to see larger, ash eruptions developing with substantial impact further afield outside the Tongariro National Park.

"The chances of a prolonged eruptive episode or a larger eruption, such as occurred in 1995-96 with wider ashfall impacts, is higher than it was two months ago, but remains very unlikely. Such an eruption would most likely only follow a sequence of smaller eruptions."

Steven warns 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.

For information on access to the Mt Ruapehu area, please visit the Department of Conservation’s websites on volcanic risk in Tongariro National Park and follow the DOC Tongariro Facebook page for further updates.

For information about responding to volcanic activity there are guidelines from the National Emergency Management Agency's Get Ready website.

You may also like....


There are no comments on this article.

Leave a Comment

You must be logged in to make a comment. Login Now