White Island Earthquakes

Dozens of small-to-moderate sized earthquakes which have struck near White Island volcano since late November seem to have caused only minor changes to the hydrothermal system on the island.

Michael Rosenberg, Duty Volcanologist at GNS Science, issued an alert bulletin for White Island volcano on Thursday afternoon, advising that there had been no significant change in volcanic activity on the island, despite the increased tectonic activity.

The earthquakes, located about 10 km north-west of the volcano, are tectonic in origin, meaning that they are part of the earthquake activity that occurs elsewhere in New Zealand. The earthquakes began at about 8:40 p.m. on November 21st with a vigorous earthquake swarm, and dozens of small-to-moderate sized events were recorded over that night. The largest event was magnitude 4.2, and the quakes ranged in depth between 5 and 20 km.

The activity has continued into December, but no immediate changes have been noted in the volcanic activity at White Island. Investigation shows that gas concentrations in the steam plume have increased to a small extent, but are still typical of the last two years. Soil gas levels are lower than levels recorded during the last 6 months, but are within longer term ranges. Fumarole temperatures are within the typical ranges for the volcano.

However, the crater lake has changed colour markedly, and vigorous upwelling and low-level geysering are reported. The crater lake level dropped rapidly during March and April this year and was only about 10 metres deep in May. It began refilling during June and its temperature, which had been at a record 74 ºC in February, declined to 64 ºC in May. Despite having risen to 67 ºC since then, it has again declined to 64 ºC during the early part of December 2007.

Weak volcanic tremor and rare small volcanic earthquakes have been recorded at White Island since November.

Whilst there have been some minor changes to the hydrothermal system at White Island, it remains at Alert Level 1 (signs of volcano unrest).

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

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