What happened?

On Monday 9 December at 2:11pm an eruption occurred at Whakaari/White Island, with significant and devastating impacts for people on the island at the time. Those affected by the eruption continue to be in our thoughts during this difficult time.

Future scenario

At 10:30am 13 December, GNS Science volcanologists reviewed all available data and updated the likelihood of an eruption that would impact beyond the vent area (marked in the image below) occurring within the next 24 hours.

Click image to make it larger. The distance between the edge of the crater lake and the ocean at the bottom of the image is about 700m.

Their new calculation was that there is still a 50-60% chance (medium likelihood) of an eruption occurring that could impact outside of the marked vent area within the next 24 hours.

The expert judgement of the likelihood of an eruption has not changed since yesterday (Thursday 12 December 2019).

How does this compare to previous estimates?

Since early 2013, eruption likelihoods for Whakaari have been calculated via expert judgement as part of internal staff health and safety procedures. Our expert scientists calculate the risk for all volcanoes at Volcanic Alert Level 1 or higher.

The table below shows the expert judgement of eruption likelihoods for time periods corresponding to when the Volcanic Alert Level (VAL) was at 1 (29 October 2019), and at VAL 2 one week prior to Monday’s eruption (2 December 2019). This is in comparison to the expert judgements conducted on 11, 12 and 13 December 2019, after the eruption. There have been other expert judgements not listed here, including one carried out on 18 November 2019 when the VAL was raised to Level 2. The last expert judgement before the eruption was on 2nd December.

For 29 October and 2 December, eruption likelihoods were calculated for 4-week and 13-week time windows respectively and have been converted in this table to reflect relevant 24-hour time windows for comparison.

The time periods used for the expert judgements vary depending on the level of activity at the volcano – when activity increases, we do expert judgements more often and for a shorter time window to reflect the changing situation.

Since the eruption on 9 December, eruption likelihoods have been calculated for a 24-hour time period. The table shows that the likelihood of an eruption is now about 100 times higher than in early December.

The Volcanic Alert Level is not linked directly to risk and likelihoods but describes the level of current volcanic activity.

Timeline of activity

Here is an annotated graph showing volcanic tremor over the last month recorded at one of our monitoring stations on the island. The 9 December eruption is shown in the red box. Also shown are the Volcanic Alert Levels for each time period. Volcanic tremor is a useful proxy for activity on a volcano, but is only one of the monitoring data streams used by volcanologists to make their expert judgements.

Attributable to: Natalia Deligne, GNS Science Volcanic Hazard and Risk Modeller

Media contact: 021 574 541 or media@gns.cri.nz