A combination of satellite images, GPS data and survey information from the 1950s have enabled scientists to uncover a magma chamber under the Bay of Plenty coast, which they link to thousands of small earthquakes here between 2004 and 2011.
Until this finding, published in Science Advances, the reason for the earthquake ‘swarm’ was thought to be tectonic. Now scientists believe the movement of magma, about 9km below the ground, triggered the swarm. The magma moving in the sub-surface weakened the surrounding rock, causing it to deform and split. This was felt as small earthquakes between magnitude 2.0 and 4.0.
The combined data reveal that the area of land around the small town of Matata, about 400 square kilometres with half offshore, has risen about 40cm since 1950. Molten or semi-molten rock has been pushed up due to the growth of this newly identified magma body.
Implementing their modelling analysis, scientists conclude that the magma body has grown significantly in volume since 1950 – predicting an increase that is equivalent to 80,000 Olympic swimming pools or 200 million cubic metres.
Lead author Ian Hamling, a satellite image specialist at GNS Science, highlights how the new findings demonstrate that accumulated magma can be found in unexpected places that are not always based on the location of volcanoes.
“Our modelling points to the presence of a magma chamber in an area where there has been no active volcanism for about 400,000 years.”
Dr Hamling notes that there are other large areas in the central North Island where bodies of magma are located.
“While there is absolutely no evidence pointing to volcanic unrest in coastal Bay of Plenty, this finding underlines the fact that we live in a geologically active country where it pays to be prepared.”
Scientists aim to model the size, depth and dynamic changes of the magma body more accurately but are dependent on further funding.
The authors of the science paper would like to thank the European and Japanese Space Agencies for access to satellite images and GeoNet for the GPS data. The research was supported by public good research funding from the New Zealand Government, with additional support from the Natural Hazards Research Platform, EQC, and Land Information New Zealand.
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