alert bulletin: Dec 13 2007, 2:00 pm - White Island Volcano

Science Alert Bulletin WIZ-07/05 - Recent earthquakes and observations; Alert Level remains at 1

For several days in late November through to early December, dozens of small to moderate-sized tectonic earthquakes occurred approximately 10 km north-west of White Island. During the earthquakes no changes were immediately noticed at White Island. Observations and analyses of recent measurements show that the volcano-hydrothermal system may not have responded significantly to the earthquakes.

As part of the routine monitoring, GNS scientists have analysed fumarole temperature and gases, and measured gas flux through the soil. Gas concentrations in the steam plume were also measured more frequently in response to the earthquakes. Temperatures of the fumaroles are well within the typical ranges for those measurements (100 - 120 °C). Soil gas levels are lower than levels recorded in the last 6 months, but are within the longer term ranges. The gas flux quantified by plume measurement of SO₂, CO₂ and H₂S gas show minor increases, but again are typical of the last two years. The crater lake has changed colour markedly, and vigorous upwelling and low-level geysering have been observed. Nevertheless, the lake’s level does not appear to have changed significantly. The lake temperature has decreased from 67 to 64 °C. Some tall steam plumes have also been observed on fine days, as atmospheric conditions allow plumes to form.

Since the November earthquakes we have also recorded some weak volcanic tremor and rare small volcanic earthquakes.

Recent monitoring indicates some minor changes to the volcano-hydrothermal system. Such changes are not uncommon in this type of system and serves to remind us this is an active volcano.

The Alert Level for White Island remains at Alert Level 1; there is no significant change in volcanic activity on the island.

Michael Rosenberg
GeoHazards Duty Volcanologist