15 may 2012

Seafloor volcanoes surprise

Science

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Volcanoes on the seafloor can grow or collapse tens of metres in just a few days, a new study has found, suggesting that that the seabed is much more unstable than previously thought.

Researchers, led by Professor Tony Watts of Oxford University’s Department of Earth Sciences, report in Nature Geoscience how they surveyed the topography of the active Monowai volcano, a submarine volcano on the southwest Pacific Ocean floor near Tonga, in May and June 2011.

The team used sonar to map the seafloor around Monowai before leaving to study another area. A week later the researchers discovered that a seismic station on Rarotonga in the Cook Islands had detected an intense five-day period of seismic activity at Monowai beginning shortly after they left. When the team returned further sonar mapping of the seafloor around the volcano revealed that whilst some parts of it had collapsed by almost 19 metres elsewhere fresh eruptions of lava had raised the volcano’s height by up to 72 metres.

Because they are underwater, and so difficult to study, little is known about how submarine volcanoes evolve or the frequency with which they erupt and grow. This new research suggests that these volcanoes could be rapidly ‘pulsating’, making the seafloor environment much more dynamic than anyone suspected; a finding that has implications for understanding what causes tsunamis.

‘I've spent my career studying the seabed and have generally thought it pretty stable so it's stunning to see so much change in such a short space of time,’ said Professor Tony Watts of Oxford University’s Department of Earth Sciences.

Seafloor volcano
Sonar was used to map the Monowai volcano, near Tonga

‘Any movement on the seabed has the potential to create a tsunami. An earthquake suddenly dislocates the seabed. Here a violent disturbance lasted five days with magma oozing out which might be too slow to trigger a tsunami - but it's unknown. This is a violent exchange of rock into the water - it could destabilise the cone and cause a landslide which in principle could cause a tsunami.’

A report of the research, entitled ‘Rapid rates of growth and collapse of Monowai submarine volcano in the Kermadec Arc’, is published online in this week’s Nature Geoscience.