Report on Whakaari/White Island (New Zealand) — September 1996
Bulletin of the Global Volcanism Network, vol. 21, no. 9 (September 1996)
Managing Editor: Richard Wunderman.
Whakaari/White Island (New Zealand) Recent heating and deformation episode appears to have ended
Please cite this report as:
Global Volcanism Program, 1996. Report on Whakaari/White Island (New Zealand) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 21:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199609-241040.
37.52°S, 177.18°E; summit elev. 294 m
All times are local (unless otherwise noted)
Observations in April, May, and July indicated continued increases in heat flow and inflation of the Main Crater floor. Low-level volcanic tremor that began in late July continued through August. Since the tremor commenced it appears that heat-flow has decreased, as has the deformation. Measurements in late August indicated that the crater-wide deformation and heating of the last 2-3 years appears to have peaked without eruptive activity. Since the last report (BGVN 21:04), monitoring visits were made on 18 April, 16 May, 24 July, and 28 August 1996.
Crater observations. On 18 April, the lake occupied Royce, Wade, Princess, and TV1 craters, with the S part of the divide between Princess and Wade craters 2-3 m above the lake. The lake was light turquoise, with a few brown surface slicks. A fumarole in the N wall of Wade Crater was audible from the edge of the 1978/90 Crater Complex; it was the only significant steam source in the complex.
Donald Mound was steaming vigorously, with that part exposed in the wall of the 1978/90 Crater Complex and the SE slopes the dominant features. Sulfur deposits were obvious on Donald Mound and the 1978/90 wall. The area of mud pots at the base of Donald Mound was also steaming vigorously. The whole area was wet and some mud pots included areas of significant sulfur deposition. Collapse was actively occurring between the 1978/90 Crater Complex and Donald Duck, causing brown slicks on the lake surface.
An ejecta apron with material up to 12 m from the vent was observed by charter pilot J. Tait on 4 June. Calm and clear conditions on 9 June allowed a tall steam plume to develop above the island; it was mistaken as an eruption plume by several coastal observers and the media. However, pilots R. Fleming and J. Tait, on the island at the time, observed no unusual activity. On 11 June R. Fleming reported a dramatic rise in lake level (>5 m) in three weeks. Strong convection in the lake caused fountaining up to 3-4 m high in the embayment below the May '91 vent.
Fumarolic discharge continued to increase on the crater floor when measured on 28 August, although temperatures had moderated somewhat since May. Springs, consisting largely of steam condensate, continued to discharge, and two new such features had developed along the boundary between the E and central sub-craters. Maximum temperatures on Donald Mound were 311°C, down ~100°C from May. A large fumarole discharging a bright yellow, sulfur-laden plume had developed ~5 m below the inner crater rim that intersects Donald Mound. The crater lake was mostly obscured by steam, but it appeared gray in color; maximum temperature as recorded by pyrometer was 69°C.
Magnetic survey. A comprehensive survey of the magnetic network was conducted on 16 May with the exception of a few sites at Donald Mound that were inaccessible due to hydrothermal activity. Contouring the changes since the partial survey on 23 January 1996 showed that the decreases at Donald Mound with corresponding increases to the S were continuing. These results suggested continued shallow (50-100 m deep) heating. A weaker negative anomaly W of Noisy Nellie, presumably resulting from heating on the N side of the complex, continued the trend observed during 6 July-12 December 1995.
A positive anomaly E of Donald Mound (site D10b) showed a change of +518 nT, although the site is near a new mud hole, so the effect may be local. Positive changes at Site G (+126 nT) and nearby sites are unusual because decreases are usually recorded when there is heating at Donald Mound. This anomaly may suggest cooling, perhaps around 100-200 m deep, at the E edge of the area of hydrothermal activity, possibly related to the rising water table.
Deformation. Levelling surveys on 18 April and 16 May were conducted over the entire network except over Donald Mound due to intense steam and hot, soft ground. Both surveys revealed broadly similar patterns and rates of continuing uplift centered on Donald Mound and extending SE. Relative subsidence continued NW of Donald Duck Crater, although part of that may be due to slumping induced by encroachment from the 1978/90 Crater Complex. The inflation pattern during the previous five months remained similar to that since Donald Mound began rising in late 1993.
A partial levelling survey was done on 28 August; three pegs near Donald Mound could not be accessed, two were lost due to crater wall collapses, and one was buried under a landslide. Since about 1992-93, levelling surveys have shown a systematic crater-wide uplift. However, this survey showed a dramatic reversal of the uplift trend, with minor subsidence observed over much of the Main Crater floor. The larger subsidences were focused about the Donald Mound area and the margins of the 1978/90 Crater Complex. These changes are consistent with the thermal changes observed on 28 August and may indicate that the present inflationary-heating episode is over or declining.
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.J. Scott, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.