NIWA confirms collapse of undersea volcano

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The aptly named ‘Rumble III’ undersea volcano on the Kermadec Ridge, 200 km northeast of Auckland, has dropped in height by 120 metres in the last couple of years, pioneering research by NIWA has shown.

“Our seabed is a lot more active than we thought,” says NIWA marine geologist, Richard Wysoczanski. “Within the last ten years there have been numerous undersea volcanic eruptions and activity: Monowai (several times up to 2008), Raoul Volcano (2006), and White Island (2000 and 2001). These volcanoes, as well as the non-volcanic ridges, can also cause landslides that could potentially generate a tsunami that would impact on New Zealand.”

NIWA scientists first mapped Rumble III in 2002 using multibeam technology. On the recentRV Tangaroa oceanographic voyage in May and June of this year, NIWA scientists confirmed that the volcano has collapsed on the western flank, closest to New Zealand.

Rumble III is one of more than 30 big submarine volcanoes on the Kermadec Arc. They form a jagged chain that ascends from the ocean floor, with Rumble III volcano larger than Mt Ruapehu.

The first leg of the Tangaroa trip focused on geophysical surveying of the Kermadec Arc seafloor and Seafloor Massive Sulphide (SMS) deposits that sometimes develop over hydrothermal vents. The volcanoes and vents are rich in iron, lead, zinc, and copper, with lesser concentrations of gold and silver.

“We are investigating these volcanoes and mineral deposits to determine their size and the biological communities they support. The research will provide industry and government agencies with the information they need to make the best decisions based on the biological and physical characterisation of the sea floor,” says Dr Wysoczanski.

The name Rumble came from Royal New Zealand Navy personnel. They named the undersea volcanoes in the 1960s when they steamed over them. In 1963, sonar hydrophones on Great Barrier Island detected rumblings from this area. Subsequent surveying by research vessels located the submarine volcanoes, which they aptly named Rumble I, II, III, IV, and V. Two volcanoes north of this were named Silent I and II, as they were outside the area of rumbling. This 2500 km stretch of volcanic seafloor marks the boundary between the Australian and Pacific tectonic plates.

Youngest known rock

Dr Wysoczanski also collected black basalt rocks from Rumble III. “It’s the youngest known rock from the Kermadec Arc region. It was created some time between 2007 and 2009. “It’s glassy, black, and full of air bubbles.”

The rocks essentially tell the origins of the volcanoes. Scientists can tell from the type of rock produced whether they have come from a deep magma chamber or from a shallow magma chamber, and how explosive the eruption may have been.

“We did 23 dredges on the Kermadec Arc, including the Kermadec Ridge, which has never been dredged before. We knew it was volcanic but we didn’t know what sort of volcanism – so it was quite exciting,” says Dr Wysoczanski.

NIWA principal scientist, Dr Geoffroy Lamarche says, “We haven’t mapped all of this area, so we still don’t have the full picture of what is there. We’ve mapped 3000 square kilometres of ‘new ground’. We need to know the value and size of these deposits. From the geophysical study, we can see where the fields are because they generate a different signal to the rest of the volcano.” NIWA is harnessing seismic reflection techniques to allow informed decisions to be made.

“You can’t walk over these volcanoes and look at the deposits. You need to image them remotely. One way of doing this is by multibeam, which allows you to get a map of the volcano. The geophysical techniques allow you to look into the inside structure of the volcano,” says Dr Lamarche.

This is the first voyage of a five-year programme funded by the Foundation for Research, Science, and Technology, in collaboration with Auckland University, GNS Science, the National Oceanography Centre, Southampton, and the Woods Hole Oceanographic Institute in the USA.

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The youngest known rock (Dave Allen)