Monowai volcano

You wouldn't know it but a large volcano eruption is taking place in New Zealand. It's not visible because Monowai is completely underwater - north of the Kermadec Islands, and is about 1500 metres deep.

Its conical cone reaches to just 120 metres below the surface of the Pacific.

French Polynesia's Laboratoire de Geophysique is taking recordings of what is going on and Dr Oliviere Hyvernaud told Fairfax they recorded a "big acoustic event on February 8". He added it was strong "but not a monster".

Monowai was in an eruptive phase but it was difficult to say whether it was a strong eruption.

In New Zealand GNS Science geologist Cornel de Ronde said French Polynesia sees the sound signals more easily than stations in New Zealand. Monowai has erupted regularly over the years, he said.

Dr Ian Wright of the National Institute of Water and Atmospheric Research has closely studied Monowai and in a paper to be published in the international Journal of Geophysical Research argues that in May 2002 the volcano itself collapsed creating an "explosive interaction and cooling of hot magma and volcaniclastic rubble with ambient seawater".

Dr de Ronde said Monowai was similar to Mount St Helen's in the United States which collapsed and then rebuilt itself over time.

The latest activity has gone unnoticed on the surface as its location is off the main shipping routes. In previous years Royal New Zealand Air Force over flights have spotted large sulphur slicks.

What was thought to be a shoal of fish was first reported in the area in 1944 but it was not until 1977 that it was recognised as a volcano. It was surveyed by HMNZS Monowai, thus its name.