Jul 31 2000, 5:00 pm - White Island Volcano

Staff from the Institute of Geological & Nuclear Sciences (GNS) visited White Island today (July 31) to examine the effects of an eruption on Thursday evening (July 27). A new large explosion crater, 120 – 150 metres across has formed and is currently discharging a reddish brown coloured gas and ash plume. The recently active MH vent has increased in size and is producing a dark coloured ash & gas plume. The steam, gas and ash plumes from the two vents are rising to 1000 m before being blown to the north-east by a moderate south-west wind. It is evident that last Thursday’s eruption generated a thick deposit (up to 30 cm) of ash, rock debris & fresh pumice blocks that has covered much of the main crater floor - an area which is frequented by visitors to the island. Pumice blocks up to 1.5 m diameter were observed. This explosive eruption is of similar style and scale to the magmatic eruptions of March - April, 1977. Thursday’s explosive eruption occurred without significant warning. Had anybody been on the island at the time of eruption it is likely that they would have been seriously injured or killed. Similar types of explosive eruptive activity can be expected in the future. These explosive eruptions clearly pose a significant risk to anyone visiting the island. The Alert Level remains at 2.

Today, staff from the Institute of Geological & Nuclear Sciences (GNS) visited White Island to examine the effects of an eruption on Thursday evening (July 27). A period of strong seismic activity occurred between about 5 pm and 10 pm on Thursday July 27, but darkness and poor weather prevented direct observation at that time. An aerial inspection was conducted on Saturday (July 29) and this confirmed that recorded seismicity was associated with a crater forming eruption. Today (July 31), GNS staff flew to the island to make direct observations, sample ejected debris and gases, and assess the status of monitoring equipment.

Thursday’s eruption has formed a large explosion crater, 120 – 150 metres across and is currently discharging a reddish brown coloured gas and ash plume. The new explosion crater is located in a small area that was formerly occupied by a shallow, warm-acid lake. This lake has now completely disappeared. The recently active MH vent has increased in size to c.50 m diameter and is producing a darker coloured ash and gas plume. The steam, gas and ash plumes from these two vents are rising to 1000 m before being blown to the north-east by a moderate south-west wind. Should strong winds be experienced from the north or north-east it is likely that this ash plume will be directed towards the mainland and possibly result in minor fine ash fall.

It is evident that last Thursday’s eruption generated a thick deposit (up to 30 cm) of ash, rock debris and fresh pumice blocks that have covered much of the main crater floor, extending at least as far as the sea, 700 metres away. Pumice blocks up to 1.5 m diameter were observed. The shapes of these blocks indicate that they impacted the ground in a semi-molten state. Thursday’s explosive eruption is of similar style and scale to the magmatic eruptions of March - April, 1977.

Had anybody been on the island at the time of Thursday’s eruption it is likely that they would have been seriously injured or killed. Further explosive eruptive activity is likely to occur in the future. These eruptive events are unpredictable and can occur without prior warning. Such activity therefore poses a significant risk to anyone visiting the island.

With the exception of the short-lived explosive eruption of July 27 and ejection of magmatic material – the current eruptive intensity is similar to that experienced since early April. The Alert Level remains at 2 (minor eruptive activity).

Steven Sherburn
Duty Volcanologist

Brent Alloway
Chief Volcanologist