A satellite found signs that predicted the Whakaari/White Island eruption - but there's a problem

Monday, 21 June 2021

The December 9, 2019 eruption of Whakaari/White Island left 22 people dead and 25 people with severe or critical injuries.

A satellite that just happened to capture gas levels before, during and after the Whakaari/White Island eruption revealed what scientists say were precursors of the event.

But there was no practical way to get the information in time to have prevented the tragedy.

A satellite capable of measuring sulphur dioxide levels in the atmosphere just happened to be passing over Whakaari/White Island almost an hour after its deadly eruption in 2019, providing scientists with a snapshot view of volcanic activity before, during, and after the eruption.

The team of researchers involved in the study say this kind of satellite data could provide new insights into volcanic activity, but there are clear limitations that mean it could not work alone.

Firstly, there is a significant delay in accessing the satellite data. The satellite observations are also highly reliant on cloud free days, and there is only one satellite pass per day.

The December 9, 2019 eruption off the coast of Whakatāne in the eastern Bay of Plenty left 22 people dead and 25 people with severe or critical injuries.

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Fifty-eight minutes after the eruption, the Sentinel 5 Precursor satellite, with its sensitive TropOMI gas detecting instrument, coincidently passed overhead.

Data that was captured by the satellite has now been reported on in a new paper in the Science Advances journal.

Dr Craig Miller, a senior volcano geophysicist, and Dr Bruce Christenson, a volcanic fluids geochemist, both from GNS Science, were co-authors of the paper.

On the afternoon of Monday December 9, 2019 Whakaari White Island erupted while tours were in progress, killing 22 people and injuring 25.

They said the satellite data provided the team of researchers with a snapshot view of sulphur dioxide – a volcanic gas – in the atmosphere around the volcano at that time.

By combining that satellite image with a high-resolution wind model, they were able to back-calculate the amount of sulphur dioxide gas that had been coming from the volcano from one and a half hours before the eruption, all the way through to 58 minutes after the eruption.

The results showed that about 40 minutes before the eruption, there was “a four-fold increase in gas flux”.

However, Dr Miller and Dr Christenson said the importance of this kind of observation as an eruption forecasting tool was tempered by the delay in accessing the data, which was usually available three to four hours later.

Whakaari/White Island eruption as seen from tourist boat.

“Globally, satellite-based gas detection has improved dramatically in the past two decades and it provides an increasingly useful tool for assessing changes on the days’ to weeks’ timescale, although challenges remain in utilising it for real-time monitoring.”

The researchers also studied satellite data from one month before and one month after the eruption and found that on multiple days there were also high gas fluxes that did not lead to eruption.

Dr Adrian Pittari from the School of Science at the University of Waikato – commenting on the new study – said detection of a sulphur dioxide plume at Whakaari did not always herald an eruption.

“But it does help to determine if the volcano is undergoing a heightened state of unrest, thus increasing the risk of an eruption,” he said.

“In hindsight, the satellite measured the plume after the 2019 eruption so it would not have made a difference to any pre-eruption warnings at that time. However, we now know that continued surveillance of sulphur dioxide plumes by this satellite adds a new tool to monitoring the ‘vital signs’ of Whakaari/White Island and our other active volcanoes in New Zealand.”

Dr Miller and Dr Christenson also said that although the satellite sulphur dioxide measurements offered promising capability to detect high gas emissions over a wider area, ground-based instruments were still required for relatively low emitters such as Whakaari.

“Since 2006 GeoNet has operated such a network of ground gas detection instruments on Whakaari and these along with seismic, geodetic (ground movement), and visual observations provide the key data streams for assessment of activity at the volcano.”

Professor Ben Kennedy from the School of Earth and Environment at the University of Canterbury – also commenting on the study – said ground-based monitoring was still needed to provide sufficiently frequent data to be useful for forecasting eruptions.

However, he said if these types of gas detecting satellites became more widespread, “creating more coincidence with days of clear weather above active volcanoes, this type of data can contribute significantly to eruption understanding”.