Report on White Island (New Zealand) — April 2000
Bulletin of the Global Volcanism Network, vol. 25, no. 4 (April 2000)
Managing Editor: Richard Wunderman.
White Island (New Zealand) Continuous ash emissions in April; high SO2 and fluctuating tremor
Please cite this report as:
Global Volcanism Program, 2000. Report on White Island (New Zealand). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 25:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200004-241040.
37.52°S, 177.18°E; summit elev. 321 m
All times are local (unless otherwise noted)
Starting on 7 March, White Island displayed minor eruptive activity, elevated seismicity, and higher than normal SO2 gas flux (BGVN 25:03). Staff from the Institute of Geological & Nuclear Sciences (GNS) who visited on 18 April observed a gas plume, comprised of steam and small amounts of ash, being erupted to 1,300-1,700 m before being blown S. At distances of more than a few kilometers from the island no ash was visible in the plume, although reports from Whakatane indicated that trace amounts of ash fell during the night of 17-18 April. The erupting vent, named MH vent, is ~10 m across. The seismograph at White Island recorded volcanic tremor starting on 6 April 2000, the first significant tremor since April 1999. In addition, recent measurements of the SO2 flux were well above typical background levels at White Island. This eruptive activity was sufficient to increase the Alert Level from 1 to 2.
Ash was erupted almost continuously during the weekend of 22-23 April, although there was no evidence that any larger blocks were erupted. During another visit by scientists on 26 April the activity level was much reduced from that of the previous two weeks, but minor eruptive activity continued. A weak gas plume, comprised almost totally of steam, was being erupted to 1,500 m before being blown NE. The plume was not visible more than a few kilometers from the island. The seismograph continued to record moderate to strong volcanic tremor, although the level fluctuated with time. It is unclear if there was a direct relationship between the intensity of the eruptive activity and the level of volcanic tremor. COSPEC measurements on 28 April recorded a SO2 flux of 927 metric tons/day, down from previous measurements, but consistent with the activity.
Activity was similar during a monitoring visit on 2 May, with a weak gas and ash plume from MH vent. The ash plume was rising to 500 m, while the steam-and-gas plume rose to 760-900 m before being blown NNE. The plume was visible more than 10-15 km from the island. Ash emission was occurring continuously. The seismograph continued to record fluctuating moderate to strong volcanic tremor.
Geologic Background. Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes; the summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE. Intermittent moderate phreatomagmatic and strombolian eruptions have occurred throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project.
Information Contacts: Brad Scott, Brent Alloway, and Steven Sherburn, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).