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Report on Whakaari/White Island (New Zealand) — February 1982

Whakaari/White Island

Scientific Event Alert Network Bulletin, vol. 7, no. 2 (February 1982)
Managing Editor: Lindsay McClelland.

Whakaari/White Island (New Zealand) Localized inflation; decreased seismicity

Please cite this report as:

Global Volcanism Program, 1982. Report on Whakaari/White Island (New Zealand) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 7:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198202-241040

Whakaari/White Island

New Zealand

37.52°S, 177.18°E; summit elev. 294 m

All times are local (unless otherwise noted)

Observers from Victoria Univ. and NZGS spent 4.5 hours the afternoon of 29 January inspecting the island and reactivating the seismograph. No tephra deposition had occurred since the last visit 2 December 1981. Tephra deposited between 18 September and December measured 46 and 23 mm at two sites on the crater rim, and was absent beyond 250 m from the active vent. Its fraction coarser than 250 µm was composed of roughly equal amounts of fresh glassy low-silica andesite (52 wt.%) and accessory, hydrothermally altered lithic material (48 wt.%).

Activity in 1978 Crater appeared less intense than in September. The depth of the active subcrater was 105 m. Vents on its floor and W wall emitted white steam. Numerous geysers jetted black muddy water to several m in the N part of the shallow bright-green pond that covered about half of the subcrater's flat floor. Many large lava blocks had fallen from the W walls; several rockfalls occurred during the observation period. The high-pressure gas vent that had been on the NW side of the subcrater floor in September was not present.

Fumaroles around Donald Mound, a 100 x 150-m area in the middle of the main crater, appeared more active than in September. Several had strong discharges of high-pressure, clear gas and some blue fume. Temperatures just E of the mound were 590°, 640°, and 655°C. Low-pressure gas in a fumarole W of it, where blue fume was condensing, had a temperature of 560°C. A large fumarole that had developed earlier on the N side of the main crater was at least 5 m deep and was emitting large volumes of white, superheated steam. Ephemeral minerals were collected on the last three visits. X-ray diffraction analysis indicated that these were predominantly unoxidized sulfur and anhydrous forms in the throats of fumaroles, and sulfate-hydrate and sulfate-hydroxide-hydrates surrounding fumaroles and their outwash areas.

The levelling survey found little tilt change between September and December, and none since December except in the vicinity of Donald Mound, where an 11-mm rise had been recorded. The inflated area was about 400 m across, centered at the E side of the Mound, about 200 m E of 1978 Crater. After a similar localized inflation, three small gas vents formed N of the Mound in May 1980.

Seismic records 21 September-19 January (when the seismograph stopped working) showed a gradual decline in the number of low-frequency (B-type) events from more than 40 to fewer than 5 per day by 10 December. The level has remained low. High-frequency (volcano-tectonic) events numbered fewer than 5/day except on: 25 November, 7 events; 16 December, 16; 21 December, 6 events; 8 January, 35 events; and 14 January, 7 events. Distinctive seismic signatures (symmetric, with emergent onsets) were recorded on 29 November, 1, 13, and 19 December, and 16 January. The NZGS interpreted these as medium-frequency volcanic earthquakes, probably intrusive events. Volcanic tremor was recorded weakly on 25-26 September, 8, 24, and 25 October, and 15 November.

Geological Summary. 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: A. Cody, B. Houghton, I. Nairn, P. Otway, B. Scott, and C. Wood, NZGS, Rotorua.