Feb 15 2007, 11:00 am - White Island Volcano

Recent visits to White Island, including one on 13 February have confirmed a continued rise in the temperature of the Crater Lake. The lake temperature has now reached 74ºC, the highest ever recorded temperature in the lake. As a result of the high lake temperatures, the lake level has fallen over 6m due to evaporation, and steam plumes are frequently seen above the island. Minor eruptive activity may now occur at the island.

In August 2006 the lake temperature started to rise from its typical 48 - 50ºC to reach over 60ºC by January 2007, and has now risen to 74ºC. This reflects a significant increase in heat flow through the volcano. This heat flow increase has accelerated the evaporation of the lake and the water level is now over 7m below overflow (it had been as high as 1m below overflow in 2005). The volume of the 400m diameter lake has decreased by 10% and seepage of lake water on the crater floor has also stopped. The major constituents in the lake chemistry have also shown increases (magnesium and chloride up by 10 - 12%) supporting the evaporation model. Overall chemical processes continue to reflect geothermal, not magmatic process.

The airborne and soil gas fluxes have shown a slight increase over the last eight months. For example the sulphur dioxide flux has risen from 300 to around 500 tonnes/day. Carbon dioxide gas flux has also increased from around 1000 to 1400 tonnes/day. As the chloride concentration in the lake rises so will the amount of hydrochloric gas being released, and some discomfort may be experienced by visitors.

The deformation surveys of the crater floor have not shown any significant changes from those observed in recent months, indicating no inflation of the crater floor as was observed before the 1976 eruptions.

Seismic activity at White Island has changed slightly since mid-January; weak volcanic tremor has appeared and continues (reflecting increased hydrothermal activity at shallow depth and the lake heating). There have also been two moderate tectonic earthquakes near by in the last month however the significance of this is uncertain. Normal minor volcanic earthquakes continue to be recorded.

In summary, the heat flow through the volcano is increasing, along with gas flux and this is resulting in rapid evaporation of the lake and the release of extra gas. The water level fall will change the pressures in the geothermal system and this may become unstable and result in minor eruptive activity.

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

Brad Scott
Volcano Surveillance Co-ordinator