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Report on Whakaari/White Island (New Zealand) — September 1987

Whakaari/White Island

Scientific Event Alert Network Bulletin, vol. 12, no. 9 (September 1987)
Managing Editor: Lindsay McClelland.

Whakaari/White Island (New Zealand) Ash eruption; tremor and eruption earthquakes

Please cite this report as:

Global Volcanism Program, 1987. Report on Whakaari/White Island (New Zealand) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 12:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198709-241040

Whakaari/White Island

New Zealand

37.52°S, 177.18°E; summit elev. 294 m

All times are local (unless otherwise noted)

The largest eruption in 3 months occurred on 7 September. After a period of declining tremor, a short-duration C-type earthquake at 1014 was followed by 2 minutes of higher amplitude tremor of mixed frequency. This peaked at 1018 before returning to background levels at 1022. The time of the main eruption was interpreted from seismic records as being between 1015 and 1022. At 1100 the ash plume extended horizontally ~10 km NW at 1 km altitude. A steam and ash column was rising to 700 m above the island. Thickness of the new ash and lapilli layer was measured at 70 mm on the E part of the crater rim 1.5 hours after the eruption. All lapilli and block ejecta seen by geologists were altered lithic material derived from vent wall country rock.

Gas and ash emission was followed by moderate ejection of incandescent ash, observed 1120-1220 from a boat 900 m from the vent (in Wilson Bay). An observer on the coast (>50 km away) noted an ash column reaching 2,000 m. No seismicity accompanied the activity. A glow in the vent area had been observed from offshore the previous night.

Seismicity had been at moderate levels since 11 June, dominated by medium-frequency volcanic tremor. A number of E-type (eruption) earthquakes were recorded 2-5 September (and probably 30 August), the first significant discrete volcano-seismic events since June. Volcanic tremor often stopped at the time of an E-type event and gradually began again a few hours later. Tremor ceased after the 1015-1022 eruption on 7 September, and restarted at about 1900.

The recent eruption was similar to but smaller than the 25 January event that began the 1987 activity. It appeared to geologists to have been dominantly phreatic in origin.

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: I. Nairn, NZGS Rotorua.