Report on Whakaari/White Island (New Zealand) — June 1988
Scientific Event Alert Network Bulletin, vol. 13, no. 6 (June 1988)
Managing Editor: Lindsay McClelland.
Whakaari/White Island (New Zealand) Phreatomagmatic eruption; seismicity
Please cite this report as:
Global Volcanism Program, 1988. Report on Whakaari/White Island (New Zealand) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 13:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198806-241040.
37.52°S, 177.18°E; summit elev. 294 m
All times are local (unless otherwise noted)
White Island's activity has changed from continuous moderate gas and ash emission to episodic short-duration discrete eruptions. The largest eruption since September 1987 occurred at 1030 on 27 April; it was slightly larger than the 14 March explosion. The phreatomagmatic eruption emitted red ash, lithic blocks, and scoria bombs. A black plume (3.5 km high) was observed >50 km away, from the Bay of Plenty coast. Ash fell into the sea and moderate ash emission continued after the initial explosion.
The eruption followed 9.5 hours of relatively weak microseismicity. Its onset was marked by 2-3 minutes of relatively low-frequency (3-4 Hz) C-type seismicity that increased in frequency (6-7 Hz) and amplitude (60 mm) between 1031 and 1033, then declined to background by 1036. Twenty minutes of low-amplitude tremor followed, with lower frequency (2-3 Hz) than before the eruption. The tremor ceased after two high-amplitude/duration-ratio A-type volcano-tectonic events at 1058 and 1100. Two more volcano-tectonic events occurred at 1254 and 1301. Medium- to high-frequency tremor had dominated seismic records in the two weeks preceding the eruption.
Numerous swarm-like A-type events were recorded 4-6 May. Medium-frequency volcanic tremor was established by 7 May but declined to background by 0200 on 9 May. Small E-type (explosion) earthquakes occurred 7 May at 1821, 8 May at 1257, 12 May at 0357 and 2541, and 13 May at 0722. Tremor reappeared 11 May and dominated records in succeeding weeks.
When geologists visited the volcano on 27 May, impact craters probably produced by the 27 April eruption extended 750 m from Hitchhiker vent to Crater Bay. Numerous ash-covered scoria bombs deposited by the same eruption were found on the crater floor. Post-14 April ejecta at the crater rim consisted of 20 mm of fine pink ash, 25 mm of coarse dark ash, and lithic lapilli. The interior walls of Fumarole 6, 200 m E of Hitchhiker vent, were incandescent. A small eruption 10 m N of Fumarole 6 had ejected lithic blocks as large as 20 cm in size.
A 15 June visit revealed no changes apart from possible minor collapse along the rim of 1978 crater. Fumarole 6 was still incandescent and its temperature had declined only slightly, to 785 from 830°C two months earlier. Hitchhiker vent emitted gas that contained a little ash. A deformation survey measured deflation of the main crater, E and NE of Hitchhiker vent. Rapid local inflation had occurred around Fumarole 6 during its strongest activity.
Since 15 June, White Island seismicity has changed significantly. Tremor became more intermittent until it ceased 18 June. E-type earthquakes occurred at 0205 on 19 June (large), 1308 on 21 June (very small), 1026 on 22 June (medium), and 0705 on 23 June (large). Only the 23 June event was associated with an observed eruption, when pilots Morter and Ford (Air New Zealand) noted a "mushrooming" eruption column rapidly rising to 3.0 km at 0710.
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: I. Nairn, NZGS Rotorua.