A period of relative quiet at White Island has ended, with increased gas emissions, an abrupt rise in the level of the crater lake and bursts of volcanic tremor.
Friday 3rd August 2012
White Island volcano in the Bay of Plenty has been relatively quiet during 2011 and 2012 while the crater lake slowly evaporated, exposing steam vents. The lake level had become so low as to make it difficult for vulcanologists to take their usual measurements, with two muddy pools being left within the volcano’s crater.
This changed in early July when the island began experiencing intermittent periods of volcanic tremor, including three periods of notable activity on July 28th, 30th and 31st. Like many volcanoes, tremor is not unusual at White Island, but the departure from the very low levels of tremor recorded earlier this year is noteworthy.
With the lake being inaccessible for some time, readings of its temperature and chemistry have not been possible for several months. However, sometime between Friday July 27th and Saturday July 28th, the lake level rose abruptly by three to five metres, accompanied by a vigorous flow of gas and steam.
Gas measurements taken on August 1st indicate an increase in sulphur gas over three months, but carbon dioxide emissions remain constant.
In addition the main crater floor, which had been subsiding, may now be slowly rising.
These changes are typical of the activity that occurs at White Island volcano from time to time. However, after a relatively quiet period, the changes in lake level, tremor, gas emissions and the crater floor level show a distinct increase in activity from that experienced in recent years. They suggest that the hydrothermal system at the island has become unstable with an associated increase in risk. The island is popular with tourists, and caution is now advised if approaching the crater lake and other active thermal features at White Island.
The Volcanic Alert Level for White Island remains at Level 1 (signs of unrest) but the Aviation Colour Code has been raised from Green to Yellow, indicating that the volcano is experiencing signs of elevated unrest above known background levels.
GNS Science continues to monitor the activity at White Island, and points out that the increased activity at the volcano has no connection with the current earthquakes and gas emissions on-shore at Mt. Tongariro.
[Compiled from GNS Science volcano Alert Bulletin published on the GeoNet website.]