Report on Whakaari/White Island (New Zealand) — August 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 8 (August 1986)
Managing Editor: Lindsay McClelland.
Whakaari/White Island (New Zealand) Continued minor phreatomagmatic activity
Please cite this report as:
Global Volcanism Program, 1986. Report on Whakaari/White Island (New Zealand) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198608-241040.
37.52°S, 177.18°E; summit elev. 294 m
All times are local (unless otherwise noted)
New ash layers indicated that small-scale phreatomagmatic activity has continued intermittently since May 1986 from "Congress Vent," which became active in February... . During a 1 August visit, geologists examined the 1986 tephra, which can be subdivided into three units. Layer 1, accumulated since 27 July, was 18 mm thick at the sampling site on the 1978 Crater rim, 50 m E of the vent. It consisted mostly of sub-millimeter ash, containing altered lithic fragments and many subrounded crystals. Some angular chips of dark gray fresh andesite and minor brown volcanic glass were also present. Layer 2 was very widespread, extending over most of the main crater floor, and was 120 mm thick at the sampling site. It appeared to have been deposited while damp. The dispersal axis of this layer probably trends N to NW from the vent and at least most of it was deposited since the last deformation survey, on 6 May. Layer 2 was similar to layer 1, but contained a larger proportion of more angular crystals and fresh andesite clasts, and less altered material. Layer 3, 155 mm thick at the sampling site, consisted of centimeter-bedded well-sorted very coarse gray ash and lapilli. Largely confined to within 50 m of the 1978 Crater rim, it was erupted in early 1986 and had formed the ground surface in early March.
Local volcanic seismicity since early May has been dominated by low-frequency (B-type) volcanic earthquakes. The number of events ranged from 15 to >40/day, and they appeared to have anomalously large amplitudes. High-frequency near-tectonic/volcano-tectonic events usually numbered < 5/day. Wide-band, long-duration volcanic earthquakes were recorded on 19, 26, and 30 June. An eruption column was reported by Geyserland Airways on 26 June.
The maximum temperature measured in the Donald Mound area (100 m E of the 1978 Crater rim) and the 1980 collapse pits to the NW was 665°C. Fumarole temperatures have generally declined in the Donald Mound area during the past eight months but have risen in the 1980 collapse pits. Temperatures and pressures of a fumarole in the easternmost collapse pit were particularly high, and the 594°C measured was well below the true temperature. The vent walls appeared slightly incandescent.
After 2.5 years, the persistent NW-SE trough of subsidence centered on Donald Mound has been virtually eliminated except for a narrow moat to the south. There appeared to be no significant height change near the eastern edge of 1978 Crater associated with the 1986 Congress Vent.
Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km 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 SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused 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. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.
Information Contacts: B. Scott, NZGS Rotorua.