New Approach to Accurately Hindcast and Forecast Explosive Eruptions at Whakaari, New Zealand

https://agu.confex.com/agu/fm23/meetingapp.cgi/Paper/1271422(external link)

Phreatic eruptions are small, sudden events, commonly with few precursory signals. They are driven by interactions between magmatic and hydrothermal processes at shallow levels beneath the surface.

Here we show that a sequence of banded tremor events, which occurred several weeks before the 9 December 2019 eruption of Whakaari (White Island), New Zealand, can be used to hindcast this eruption. The banded tremor sequence reveals a progressively decreasing time interval between tremor bands, as revealed by both manual and automatic detection methods. Extrapolating the tremor bands to a time interval of zero provides an accurate estimate, at least one week prior to the eruption, to within 5.52 hours of when the eruption would occur. A similar set of tremor signals appeared before the 27 April 2016 eruption, and these signals provide a very accurate hindcast of this eruption to within 2.28 hours.

These two banded tremor sequences which lead to eruption are indicative of progressive pressurization of the shallow hydrothermal system by magmatic fluids, followed by progressive seal weakening which ends in eruption. Our analysis indicates that this potential forecasting approach may prove useful for successfully and accurately forecasting future eruptions at Whakaari, should similar signals recur. The approach also may be applicable to other volcanoes similar to Whakaari which experience sudden phreatic and phreatomagmatic eruptions. Future challenges include unrest episodes with banded tremor but no eruption, and effectively using manual and automatic detection to forecast and possibly predict eruptions.