Active volcano White Island is showing signs of increased activity and that has prompted GNS to lift the aviation alert level from green to yellow for pilots flying over and near the Bay of Plenty region.
The Crater Lake at White Island has recently started to re-fill and gases are now vigorously streaming through it says GNS in a release issued this afternoon. "Airborne gas measurements made yesterday show that the discharge of some sulphur gases has increased. During the past few weeks there has also been some minor volcanic tremor" says the statement by Duty Volcanologist Michael Rosenberg.
"During 2011and early 2012 White Island Crater Lake slowly evaporated to expose steam vents and form two large muddy pools. However, sometime between Friday July 27 and Saturday July 28, the lake level rose quickly by about 3 m to 5 m. Vigorous flow of gas and steam through the new lake can be seen from the air".
GNS says the lake has been inaccessible for many months and they have not been able to measure changes in its temperature or chemistry. "Sulphur gases measured yesterday in the steam and gas plume have increased during the last three months but CO2 gas output remains at about the same level" the statement says.
Since early July there have been intermittent periods of volcanic tremor, including several hours early on Saturday July 28 and during Monday and Tuesday this week. Tremor is not uncommon at White Island but earlier this year it had been at very low levels.
A recent ground survey showed that the main crater floor is no longer subsiding and now may be slowly rising.
These phenomena are typical for White Island's activity, but are the first substantial changes to occur in the last few years.
The statement goes on to say White Island is an active volcano but recent changes in activity suggest that the hydrothermal system has become unstable, and as a result the risk has increased.
GNS advises extra caution should be taken, especially if approaching the Crater Lake and other active thermal features.
GNS Science volcanologists are monitoring the activity and further information will be released as soon as it is available.
The increased activity at White Island has no connection with the recent earthquakes and changes in gas flux at Tongariro volcano.
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