White Island Crater Refilling

The crater lake at White Island is refilling, with the water temperature remaining hot while steam, gas and mud emissions from the largest nearby vent increase.

GNS Science published an alert bulletin for White Island volcano in the Bay of Plenty yesterday, Thursday the 23rd of October 2008. The bulletin reports changes at the volcano, but the Volcanic Alert Level remains at 1 (signs of unrest).

During the latter part of 2007, White Island’s crater lake level had been dropping, and the lake had almost completely evaporated by late October. This process reversed during December, with the lake refilling. The lake has now risen by about 15 metres and sits at about 9 metres below overflow.

Water temperature inside the lake has remained hot at 57 ºC, but well below the 74 ºC recorded in February 2007. The lake colour has changed to a light green indicating that it contains little suspended sediment.

An area of high temperature fumaroles sits about half-way between the lake and the sea on the south side of the main crater floor. These fumaroles, usually at temperatures of 101-103 ºC, have been increasingly active for several years, alternating between wet and dry, depending on the water level in the crater lake.

During recent weeks, the largest vent in the area of high temperature fumaroles has responded with steam, gas and mud emissions increasing and creating acid rain. Deformation surveys and soil gas mapping have also shown changes in the fumarole area as it has heated and increased in activity. These changes are typical and reflect the rising water levels on the island and variations in the shallow geothermal system.

White Island last erupted in 2000, from a vent that is now beneath the lake. Scientists regularly monitor the volcano, studying its response to other geological activity.

Following the very shallow magnitude 5.4 earthquake located 10 km south-west of White Island on the morning of Friday 13th June 2008, volcanologists were concerned that the nearby volcano might be disturbed by the tremor. However, while earthquake activity in the area was elevated for some days with several hundred aftershocks being recorded, the volcano went through a brief period of heightened activity starting Sunday morning, with increased volcanic tremor and some volcanic earthquakes before becoming quiet again on Monday June 16th. Such activity is common at White Island and was not considered significant.

Another burst of earthquake activity near White Island during November 2007 also failed to disturb the volcano. The earthquakes, located about 10 km north-west of the volcano, were tectonic in origin, meaning that they were part of the earthquake activity that occurs elsewhere in New Zealand. The earthquakes began at about 8:40 p.m. on November 21st with a vigorous earthquake swarm, and dozens of small-to-moderate sized events were recorded over that night. The largest event was magnitude 4.2, and the quakes ranged in depth between 5 and 20 km. The activity continued into December, but no immediate changes were noted in the volcanic activity at White Island.

Yesterday’s bulletin from Steven Sherburn, Duty Volcanologist at GNS Science concludes that, while the crater lake is refilling and the geothermal system is responding to rising water levels on the island, there is no significant change in volcanic activity at White Island. The Volcanic Alert Level remains at 1.

[Compiled from data provided by the GeoNet project and its sponsors EQC, GNS Science and FRST.]

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