The level of the crater lake at White Island volcano has dropped rapidly during March and April. At the beginning of March 2007, the lake was 9 metres below overflow, but this has rapidly declined by 19 metres.
In an Alert Bulletin issued yesterday, GNS Science Volcano Surveillance Co-ordinator Brad Scott reported that the hot lake is now only about 10 metres deep, having declined by 19 metres in less than two months.
The lowering of the lake level has exposed many steam vents and fumaroles, allowing the lake to cool by 10 degrees to 64 ºC. This explains the steam plumes, some rising as high as 3,000 metres (10,000 feet), which have been seen over the island volcano recently. Despite some of the plumes having been reported as eruptions, no such activity has occurred.
The cooling is probably due to less heat being transferred into the lake as the high temperature steam vents have been exposed. However, Scott points out that, with the lake only 10 metres deep, further falls will change the pressure in the geothermal systems and local steam explosions may result during periods of instability.
The bulletin fails to mention the short periods of volcanic tremor seen on the publicly available seismograph at White Island in recent weeks. However, it states that data to hand does not indicate an increase in volcanic activity in the near future.
[Compiled from data provided by the Geonet project and its sponsors EQC, GNS Science and FRST.]