Voluminous emission of lithic-dominated fine ash continued into May from three vents in the 1978/92 Crater complex. No obvious changes have occurred to crater morphology since the formation of a new collapse crater (Princess) in mid-April.

No ash was being emitted during 5 May fieldwork. Most of the gas emission occurred from a crater (Wade) that had ... enlarged considerably since February 1992. It occupied much of the floor of the 1978/92 Crater complex, with only narrow divides separating it from neighboring craters TV1... and May 91. A few ash-free ballistic blocks, apparently erupted from Princess Crater since heavy rain two days earlier, had fallen within ~50 m of the 1978/92 crater rim.

When geologists returned on 12 May, voluminous clouds of steam and light-gray ash were emerging from Princess, Wade, and TV1 Craters. The Wade/Princess and TV1/Princess pairs were sometimes simultaneously active. Ash from Princess Crater collected at 1125 was in accretionary flakes 1-3 mm across, composed of silt- to sand-sized pulverized andesite, along with much hydrothermal opal-C, anhydrite, natroalunite, and pyrite. Additional blocks, probably from TV1 Crater, had been deposited in an arc extending 50-100 m E of the 1978/92 complex rim. Fine gray ash coated the blocks, about half of which were weakly vesicular to scoriaceous andesite with xenoliths of thermally altered lithic material. Fractures on the N side of the subsided area, which developed next to Princess Crater in mid-April, suddenly began emitting steam along a zone 20-30 m long at about 1100; Princess Crater was active at the time, but neighboring TV1 was not. Fresh-looking, tephra-free surfaces suggested that movement was continuing along new fractures at the S wall of Main Crater. A trench dug at the rim of the 1978/92 Crater complex revealed 1.5 m of tephra accumulation since April 1991.

Seismicity showed little change since late April. A-type events were recorded 1-11 times a day, while B-types were less than 6/day. Variable-frequency volcanic tremor continued until about 27 April in 2-18-hour episodes. No additional tremor was evident until 13 May, when medium-frequency, low-amplitude signals followed an E-type eruption signature at 0843 (see below). The occurrence of tremor continued to correlate well with observed ash emission. E-type eruption signatures were detected 21 April at 1758; 26 April at 0804, 1425, and 2008; 27 April at 0116; 2 May at 2157 and 2208; 8 May at 0816; 9 May at 0724; 10 May at 0905; 11 May at 0040; 13 May at 0843 and 0855; 14 May at 0452 and 0629; and 17 May at 0119 and 1135. The last event was associated with an ash eruption seen during a COSPEC survey, which yielded an average SO₂ emission rate of 350 t/d; see table 9 for a comparison with previous COSPEC data. The eruption, observed at 1139, fed a billowing cloud that rose 2,000 m. SO₂ in the leading edge of the cloud corresponded to an emission rate of 950 t/d.

Table 9. SO₂ emission measured by COSPEC at White Island, December 1983-May 1992. Courtesy of P. Kyle and W. Giggenbach.

Deformation data showed continued subsidence E of the 1978/92 Crater rim (in the Donald Mound area) at rates that were apparently only slightly lower than in 1991. No acceleration in deformation had been detected over the April 1992 subsidence area in the 16 months preceding December 1991. Magnetic and gravity changes were small. Fumarole temperatures measured by an IR pyrometer have declined since March. The maximum value in mid-May was 211°C, probably depressed by heavy rains the preceding week.

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, DSIR Geology & Geophysics, Rotorua.