Report on White Island (New Zealand) — May 2000
Bulletin of the Global Volcanism Network, vol. 25, no. 5 (May 2000)
Managing Editor: Richard Wunderman.
White Island (New Zealand) April-May seismicity and emissions appear independent
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, 25:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200005-241040.
37.52°S, 177.18°E; summit elev. 321 m
All times are local (unless otherwise noted)
Staff from the New Zealand Institute of Geological & Nuclear Sciences (GNS) visited White Island on 8 June to assess the volcano status and do routine seismograph maintenance. The level of activity was similar to that reported over the last two months (BGVN 25:03 and 25:04). The MH-vent was producing a weak gas-and-ash plume, which was rising 800-1000 m before being blown to the NNW. The plume was visible 20-30 km from the island as a lightly colored haze.
Seismic activity had declined almost to background levels. Seismicity started to increase about 5 April, peaked about 12 May, and subsequently declined. Meanwhile, the nature and intensity of the eruptive activity had not changed significantly, confirming earlier assessments that no direct relationship existed between the intensity of the eruptive activity at MH-vent and the level of seismic activity.
White Island has now been at Alert Level 2 for ~50 days. While the intensity of the activity has varied slightly over this period, ash emission has occurred almost continuously and fresh ash now covers the island at thicknesses ranging from several millimeters to several centimeters. The style of eruptive activity has not changed during this time. The height of the ash-and-steam plume has varied with eruption intensity and wind strength, but 800-1000 m has been typical.
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 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/).