SCIENCE ALERT BULLETIN: WIZ-02/01
2.30 pm Monday, 9 December 2002

White Island Volcano update: Volcanic tremor signals

Since November 21 weak volcanic tremor has been recorded at White Island. The level has fluctuated since that time, being stronger today. The volcanic tremor todate, has been accompanied by booming sounds, shockwaves in the steam plume above the active vent and some ejection of small ballistic blocks about the active vent. A surveillance visit was made last week, but activity was milder than the tour operators were reporting. Fumarole temperatures ranged from 97.5 to 147.7°C, all being similar to measured values over the last few months.

The emission from the active vent was not particularly vigorous during our visit, and is certainly well below that seen over the last couple of years. Small explosions were occurring and shock waves could be seen in the steam plume. Some ballistic blocks lay around the active vent, there being no sign of ash emission.

However there is a significant area of heating occurring to the east of the active vent and into the lake on the crater floor. Fumarole fields like this can precede crater formation, which is often an explosive process. Past activity indicates that significantly larger eruptions, some ejecting large rocks well beyond the active vent, could occur with little or no warning. Such larger eruptions would pose a significant hazard to anyone on the island at the time.

Caution should be exercised when visiting the island now that background activity is increasing.

As there is no significant change in activity the Alert Level for White Island remains at Alert Level 1.

Brad Scott
Volcano Surveillance Coordinator

For further volcano information see http://www.geonet.org.nz
For Science Alert Bulletins see http://www.gns.cri.nz/what/earthact/volcanoes/bulletins.html
For an explanation of the alert levels see http://www.gns.cri.nz/what/earthact/volcanoes/alertl_2.html