Whakaari/White Island eruption: Update #16

Published: Fri Dec 20 2019 1:45 PM

Volcanic Alert BulletinWI – 2019/28
Fri Dec 20 2019 2:00 PM; Whakaari/White Island Volcano
Volcanic Alert Level remains at 2
Aviation Colour Code remains at Orange

We have confirmed that very hot gas and steam are being discharged from active vents at the back of the crater basin. Volcanic tremor continues at a low level. Further eruptions are unlikely in the next few days. The Volcanic Alert Level remains at Level 2.

Since the eruption on Monday December 9th, no further eruptive activity has occurred. The level of volcanic tremor remains low and new data and observations show strong flows of steam and gases continuing from the new vent area.

An observation flight yesterday afternoon (Thursday 19th), confirmed open steam and gas vents, one of which is discharging at more than 650 °C. This data confirms our previous interpretations that shallow magma is below the vent area. No magma or lava was seen.

Data processed from yesterday’s gas-measuring flight confirm that high levels (~15 kg/s) of sulphur dioxide continue to be discharged. The values are slightly lower than those (~20 kg/s) measured on December 12th.

Aerial observations yesterday clearly showed that a moderately small part of the southwestern slope of the 1914 landslide (inside the crater rim and opposite the former viewing area) has collapsed into the crater lake area including the area of the active vents, leaving a 12-metre-high scarp. This collapse occurred during or immediately following the eruption, but the area is known as a previously unstable area and will continue to be monitored.

The expert judgement made this morning calculated the likelihood of another eruption occurring between now and midday Monday 23rd. This judgement translates to another eruption being unlikely (10 - 20 %) within any 24-hour period through to Monday midday.

Consequently, the distances for GNS Science staff-access zones have been reduced. This will be reviewed again on Monday December 23rd, or sooner if required.

An explosive eruption from the main vent area remains possible and could still occur with no precursory activity, especially if there is a collapse of unstable material around one of the vents, or if the gas emission decreases markedly, allowing water to enter the vent. Sudden steam/gas eruptions from other active vents are also possible.

Should any explosive activity produce an ash cloud there remains an extremely low likelihood of ash affecting the mainland in the next 24 hours.

The Volcanic Alert Level remains at Level 2.

The Aviation Colour Code remains at Orange.

Volcanic Alert Level 2 indicates moderate to heightened unrest with potential for eruption hazards.

The Volcanic Alert Level reflects the current level of volcanic activity and is not a forecast of future activity.

GNS Science and our National Geohazards Monitoring Centre continue to closely monitor Whakaari/White Island for further signs of activity. We are providing updates on the volcanic activity and estimates of eruption likelihood as required to support operations.

Enquiries related to the emergency response should be directed to National Emergency Management Agency (NEMA).

More information will be made available within the next 72 hours, or sooner if required.

Michael Rosenberg

Duty Volcanologist

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