Earthquakes Near White Island

A burst of earthquake activity near White Island has prompted Geonet to issue an alert bulletin for the volcano.

The swarm of earthquakes began at 8:40 p.m. on Wednesday 21st November, at a location about 10 km north-west of White Island volcano in the Bay of Plenty. Sparse coverage by seismic stations in the Bay of Plenty is hampering accurate analysis of the events, but the swarm has been described as “vigorous” with the largest events believed to be magnitude 4.2 at depths between 5 and 20 km. Dozens of small to moderate events have been recorded, and the activity is continuing.

No apparent changes in the volcano have been observed, with tremor levels similar to those recorded over the past few months, and visual observations indicating no change in hydrothermal activity. However, the local and regional earthquake activity may have perturbed the hydrothermal system, and any changes could result in local steam explosions.

The Alert Level for White Island remains at 1.

The previous alert bulletin for White Island, issued on May 3rd, reported a rapid decrease in the level of the crater lake, which had plunged 19 metres during April. The lake temperature had cooled slightly, dropping 10 ºC from its unusually high temperature of 74 ºC, and steam plumes had been seen rising as high as 3 km (10,000 feet) on suitable occasions.

HazardWatch, which ceased providing regular reports on New Zealand volcanoes in June, reported that activity at White Island had eased during May and June 2007 and that, toward the end of June, the crater lake was refilling.

White Island last erupted between March and September 2000 when a new vent emitted ash, the crater lake was displaced and a new explosion crater 150 m across was formed.

[Compiled from data provided by Hazardwatch and the Geonet project and its sponsors EQC, GNS Science and FRST.]

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