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Scientists witness dramatic growth spurt at submarine volcano - 15/05/2012

Scientists have found a submarine volcano in New Zealand waters that has undergone the fastest episode of collapse and growth ever recorded at a volcano.

Monowai

The Monowai Cone, part of the Monowai Volcanic Centre, is a giant submarine volcano about 1000km northeast of the North Island that underwent a mighty geological upheaval during five days in mid-2011, and provided scientists with new insights into the behaviour of submarine volcanoes.

The volcano added about 8.5 million cubic metres of lava and debris to its summit during the brief period it was under observation.

The newly erupted material raised the summit area by 79m, while a collapse at another part of the summit saw a sudden height reduction of 19m. The volcanic growth structures included at least four new summit cones.

The observations were made unexpectedly during a three-week survey of the volcanoes in the Kermadec Arc from the German research ship Sonne.

The findings have been published this week in the prestigious science journal Nature Geoscience. One of the joint authors of the paper was marine geologist, Cornel de Ronde of GNS Science.

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“The rate of change we observed is a reminder of how rapidly geological processes such as submarine volcanism and landsliding can occur.”

Dr Cornel de Ronde

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Dr de Ronde said as well as providing insights into the dynamics of seafloor volcanism, the observations had implications for geohazards such as tsunami.

“It’s well documented that any sudden displacement of the seabed has the potential to trigger a tsunami. Submarine landslides and submarine volcanism can set off a tsunami that can travel across the ocean,” he said.

Monowai is one of the most active submarine volcanoes in the Tonga-Kermadec arc, a 2500km-long chain of submarine volcanoes stretching from New Zealand to just north of Tonga.

Geophysical surveys from research ships dating back to the early 1980s had shown regular and significant changes to the summit area of Monowai. But the changes observed in mid-2011 were the most dramatic and rapid seen to date.

The scientists estimated that in a four-year period starting in 2007, Monowai volcano could have undergone up to a dozen growth and collapse phases.

The scientists suspected a growth spurt was underway when they approached Monowai on the Sonne in May 2011 and observed discoloured seawater and gas bubbles rising above the volcano.

Monowai map 2012

During this period, seismic stations at several Pacific Island locations, including the Cook Islands, recorded a five-day swarm of shallow earthquakes located at Monowai.

When the Sonne returned to Monowai later in the three-week voyage, the scientists found part of the Monowai summit had collapsed and another part had grown substantially.

The new material at the summit was most likely erupted ash and volcanic debris, Dr de Ronde said.

The scientists believe the rapid changes they observed were larger than at most other volcanoes. Only Mount St Helens and Mount Vesuvius had recorded larger growth rates.

“The rate of change we observed is a reminder of how rapidly geological processes such as submarine volcanism and landsliding can occur.”

Dr de Ronde said the rapid growth rates at Monowai helped to shed light on the factors that controlled the ‘emplacement of surface magma’ at submarine volcanoes.

The contributing factors included the gas content of the magma, the upward pressure regime, crustal thickness, the tectonic setting, and local stress field.

“It’s remarkable that we were able to capture such dramatic geomorphic changes on the seafloor within the duration of a single research voyage.”