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Report on Whakaari/White Island (New Zealand) — August 1998

Whakaari/White Island

Bulletin of the Global Volcanism Network, vol. 23, no. 8 (August 1998)
Managing Editor: Richard Wunderman.

Whakaari/White Island (New Zealand) Non-seismic eruptions confirmed during 31 August visit

Please cite this report as:

Global Volcanism Program, 1998. Report on Whakaari/White Island (New Zealand) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 23:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199808-241040

Whakaari/White Island

New Zealand

37.52°S, 177.18°E; summit elev. 294 m

All times are local (unless otherwise noted)

On 21 August steam-and-gas plumes were reported rising to 1,500 m above White Island. There was no significant change in seismicity at that time, so the plume was taken to be atmospheric in nature (it is common for tall vapor plumes to form above the island on the first day of clear weather after a frontal system has passed). Visits by tour operators, however, indicated that on 22 August the plume was gray colored and presumably ash-laden, and on 23 August red colored. None of this activity was accompanied by seismic signals. A surveillance team visited on 31 August to confirm eruptive activity, make a ground deformation survey, and sample fumaroles and newly deposited ash. The hazard status was raised to Level 2.

A new active vent had arisen in the NW corner of the 1978/90 Crater Complex, in an area characterized by high-temperature fumaroles and gas vents over the last 2-3 years. This vent was in approximately the same area as one formed in May 1991. A maximum temperature of 463°C was measured for the venting ash column at the point of discharge. The progression from high-temperature fumarole, to active vent, and eventually active crater has been a common process at White Island. The lake on the floor of 1978/90 crater was greenish-brown in color, cool (20°C), and lacked visible zones of up-welling lake water.

Numerous impact craters had covered the mud flats adjacent to the lake. There were numerous fumarolic discharges on the crater floor, many of which appeared accessible since a collapse feature called "The Sag" had formed a rampart into the main crater. Visible cracking had appeared on the crater floor adjacent to The Sag and steam (at ~90°C) discharged through these cracks; sulfur was actively precipitating in the largest vents. This area is now unsafe to approach.

The ground-deformation survey revealed that inflation of the crater floor was reoccurring. Several survey marks that showed uplift until 1995-96, followed later by minor subsidence, had reversed again and uplift was observed. Experience from the 1976-82 eruption episode suggests that uplift occurs before eruptive episodes. Large-scale subsidence was apparent in The Sag area, with a drop of over 1,300 mm recorded (beyond Peg M). This subsidence overrode all deformation signals from the active vent in this area. Further collapse can be expected.

The volcanic ash deposit included two distinct layers. The lower one consisted almost entirely of varied and intensely altered fine white tuff together with altered lava chips; gypsum crystals were present as a minor component. This was interpreted as hydrothermally altered vent-filling detritus ejected during the opening phases of the newly active vent. The upper layer consisted of mixed altered fine detritus and fresh andesite crystals and matrix, but without pumiceous scoria clasts. Once cleared of altered debris, the vent appears to have discharged ash containing a high component of very fresh andesite. However, the lack of pumice or scoria suggested that the vent was not discharging directly from magma but possibly from the solidified carapace above a shallow degassing magma body.

Fumarole temperatures were generally lower than on previous visits, probably reflecting recent heavy rains. Fumarole 1 had a maximum temperature of 101.2°C (down from ~111°C in April), and the discharge remained CO2-enriched (water depleted). All fumaroles on Donald Mound were at or below the boiling point with low discharge pressures. Noisy Nellie's temperatures had declined since April (from 153 to 126°C), but the pressures had apparently increased. Steam also discharged around the rim of Noisy Nellie flat, and a new fumarole discharged strongly on the E slope of the hill adjacent to Noisy Nellie crater. Fumarole 13a temperatures, at 105°C, were 8°C lower than in April and the discharges appeared to be CO2-enriched.

Observations from the crater floor were generally consistent with increased degassing associated with new eruptive activity. It is anticipated that fumarolic discharge temperatures will increase as the hydrothermal system heats up. None of the eruptive activity had been accompanied by seismic signals; this is very unusual for White Island and if it persists it will be difficult to remotely assess activity.

The uninhabited 2 x 2.4 km White Island is the emergent summit of a 16 x 18 km submarine volcano. The island consists of two overlapping stratovolcanoes; the summit crater appears to be breached to the SE, where the shoreline conforms to several notches in the SE crater wall. Intermittent steam and tephra eruptions have occurred throughout the short historical period, but activity at White Island also forms a prominent part of Maori legends.

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: B.J. Scott, Manager of Volcano Surveillance, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: https://www.gns.cri.nz/).