Giant pumice island floating in Pacific
A GIANT floating island of pumice was created when a previously dormant volcano erupted amid more than 150 earthquakes over two days last month, scientists say.
The eruption of the Havre volcano, about halfway between New Zealand and Tonga, is believed to have caused the 7500sq/km pumice “raft”, which was encountered by a New Zealand navy ship early this month.
Principal scientist of the Institute of Geological and Nuclear Sciences, Cornel de Ronde, says the source of the pumice has been identified in co-operation with French researchers in Tahiti who monitor earthquakes in the south-west Pacific.
“When they looked at their physical records they saw that on July 17 and 18 there were some 157 earthquakes of magnitudes between three and 4.8,” he says.
Dr de Ronde says they occurred near the time of the first sighting of the pumice raft, and when the institute looked at its database it found the Havre volcano, which it had previously surveyed.
It was a caldera volcano, like White Island, 50km off the west coast of New Zealand’s North Island, which erupted last week.
But the Havre, 1100m beneath the Pacific Ocean, was not thought to have erupted before.
Dr de Ronde says the pumice island was so light that it had floated several hundred kilometres from the volcano when it was encountered by the HMNZS Canterbury, which took samples last week.
Scientists were also analysing samples of rock ejected from Mount Tongariro, on New Zealand’s North Island, to try to find out why it erupted a week ago for the first time in 115 years.
A caldera is a cauldron-like volcano formed by the collapse of land after a volcanic eruption.