Flow of Auckland data puts focus on volcano eruption rates

The rate of activity in the Auckland Volcanic Field (AVF) in the upper North Island of New Zealand has been increasing for the past 60,000 years, suggesting that the field is still in its infancy.

Recent DEVORA (DEtermining VOlcanic Risk in Auckland) research has underlined the unpredictably of eruptions in the AVF, and the difficulty in forecasting major events.

The late-Quaternary period monogenetic (multi-vent) basaltic volcanic field last erupted about 550 years ago.

However, recent dating of several AVF centres using the Ar/Ar isotopic method has helped to highlight the complexity of the area’s history, with new analyses increasing the number of well-dated AVF centres to 35.

The overall AVF age data indicate an onset of volcanism at about 193,200 years ago, an apparent six-eruption flare-up from 30,000 to 34,000 years ago and a 10,000-year hiatus between the last and penultimate eruptions.

Together with the major variation in eruption volumes, and the large size and unusual chemistry within the latest eruptions – Rangitoto 1 and Rangitoto 2 – DEVORA’S results reveal a complicated history.

The results show that averaging the number of eruptions over the life-span of the AVF to yield an average eruption rate is too simplistic, given the rate has changed with time.

Research has also uncovered multiple centres with unusual fossil magnetic inclination and declination that fit into several geomagnetic excursions (known times of change in the Earth’s past magnetic field) and these data help constrain the isotopic ages.

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