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Report on Whakaari/White Island (New Zealand) — August 1990

Whakaari/White Island

Bulletin of the Global Volcanism Network, vol. 15, no. 8 (August 1990)
Managing Editor: Lindsay McClelland.

Whakaari/White Island (New Zealand) Block eruption; significant morphologic changes in 1978 Crater

Please cite this report as:

Global Volcanism Program, 1990. Report on Whakaari/White Island (New Zealand) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199008-241040

Whakaari/White Island

New Zealand

37.52°S, 177.18°E; summit elev. 294 m

All times are local (unless otherwise noted)

Late-August fieldwork revealed significant morphologic changes to 1978 Crater, which had deepened and extended 30-50 m E since May. A narrow zone of newly erupted lithic blocks extended several hundred meters from a vent E of the 1978 Crater complex.

During a 29 May visit, Ashley Cody found no significant changes since 17 May fieldwork (BGVN 15:05). Fresh impact craters had apparently been formed by small blocks erupted from the new pit vent observed 17 May on the E side of R.F. Crater. Ash and "gravel" was reported falling on fishing boats anchored on the N side of White Island 29-30 June.

When geologists returned on 30 August, blocks had fallen in a zone ~100 m wide extending several hundred meters SE from Donald Duck vent (E of 1978 Crater). In the tephra-fall zone within 150 m of the vent, the ground was almost completely covered by blocks up to 1 m across. Farther from the vent, blocks to 0.3 m occupied scattered impact craters with the most distant blocks ~450 m away. A gray ash deposit thickened toward Donald Duck, from 20 mm roughly 100 m SW of the vent, to 330 mm at a site 5 m from the rim. No fresh magma was noted in any of the ejecta. Donald Duck vent had deepened and enlarged to a pipe 2-3 m in diameter extending down to the NW at a shallow angle to the horizontal. Moderate amounts of non-incandescent gas were being emitted from the vent. To the N, gas emission from Noisy Nellie was the strongest it had been in several years, causing ground vibration nearby. The vent had slightly enlarged and deepened, and had deposited a continuous coarse tephra cover that extended 30 m S. A minimum temperature of 370°C was measured (by Minolta-Land infrared sensor) during a 1 September visit, compared to 459° on 17 May. Activity at other fumaroles was at low intensity.

The 1978 Crater complex had deepened and enlarged considerably since May. No eruptive activity appeared to have accompanied the collapse episode and it was not associated with any unusual seismicity, suggesting that it was triggered by recent heavy rainfall. On 30 August, the crater's E wall was 30-50 m E of its 17 May position, and ground cracking extended ~10 m farther E from the nearly vertical crater wall, suggesting that further collapse was likely. Within the crater, the dividing wall between R.F. and Congress Craters had been removed. R.F. Crater was the deepest part of the complex, and was occupied by a green lake with a few small steaming areas around its edges. Material that had collapsed from 1978 Crater's E wall formed a landslide deposit across its E floor. A deformation survey revealed subsidence centered on Donald Mound (S of Donald Duck vent) exceeding 20 mm since 17 May, reversing two months of inflation. However, one site just S of Donald Duck vent showed a 289 mm decrease, suggesting incipient ground failure.

Seismic instruments resumed operation 20 May, recording 5-13 A-type (high-frequency) events daily until the onset of a swarm on 14 June. During the next two days, >120 A-type shocks were detected, reaching about ML 2.7. The swarm ended with an E-type eruption earthquake that had an unusually low dominant frequency and lasted ~45 minutes. Additional E-type episodes with durations of 28-35 minutes followed, again with lower-than-usual dominant frequencies. A-type events declined until 25 July, then increased again to ~10/day. Another swarm of >80 shocks (maximum ML 2.1) occurred 28 July, then A-type events declined to ~5/day. B-type (low-frequency) volcanic earthquakes were recorded on most days after 20 May, initially exceeding 20/day but soon declining to < 5/day. After the 14-16 June swarm, the number of B-type events increased sharply for two days, then dropped to 5-10/day, remaining at that level through August. Other E-type (eruption) earthquake sequences occurred at the end of May, with four of similar size, 6-15-minute durations, and lower-than-usual dominant frequencies shortly after seismic recording resumed. An isolated 7-minute E-type event on 13 July was of distinctly higher dominant frequency. Five E-type episodes have occurred since 13 August, most recently on the 24th, all with high-frequency codas but short (2-14-minute) durations. No tremor has been recorded.

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 and B. Scott, NZGS Rotorua; P. Otway, DSIR, Wairakei.