Report on Whakaari/White Island (New Zealand) — July 1981
Scientific Event Alert Network Bulletin, vol. 6, no. 7 (July 1981)
Managing Editor: Lindsay McClelland.
Whakaari/White Island (New Zealand) Volcanic seismicity declines; no sign of tephra ejection since May
Please cite this report as:
Global Volcanism Program, 1981. Report on Whakaari/White Island (New Zealand) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 6:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198107-241040.
37.52°S, 177.18°E; summit elev. 294 m
All times are local (unless otherwise noted)
A routine surveillance flight by NZGS personnel was made on 13 July from 1034 to 1057. Weak gas and steam emissions from the fumaroles and vents rose to 600 m and showed no sign of ash. The main crater floor appeared dark gray-brown near the active vent, but reddened away from it. Distinct yellow-green areas were visible both on the S side of the crater and on the N outer slopes. A tan area was also on the S side. Numerous impact craters of more than one generation extended about 600 m E of the active vent and were concentrated about 300 m from it. All the impact craters had subdued margins. Tephra deposits were extensively gullied. Although discrete explosive events had occurred, there had been little tephra emission since the previous visit on 21 May.
Seismic records revealed a contined decline in activity, apparent since early this year. Since 21 May a marked decline was evident in the number of low-frequency (B-type) events from more than 30/day to about 5/day. Volcanic tremor was recorded on 26 and 30 May; 3-4, 6, 12, and 28 June; and 2, 5-6, and 8 July. High-frequency (volcano-tectonic) events numbered fewer than 10/day except during 14-15 June, when several hundred per day were recorded. The increased high-frequency activity was accompanied by distinctive, medium-frequency seismic signatures which were symmetric and had emergent onsets. NZGS personnel interpreted these as volcanic earthquakes and, possibly, intrusive events.
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.