Report on Whakaari/White Island (New Zealand) — September 1991
Bulletin of the Global Volcanism Network, vol. 16, no. 9 (September 1991)
Managing Editor: Lindsay McClelland.
Whakaari/White Island (New Zealand) Continued explosions from May vent
Please cite this report as:
Global Volcanism Program, 1991. Report on Whakaari/White Island (New Zealand) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 16:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199109-241040.
37.52°S, 177.18°E; summit elev. 294 m
All times are local (unless otherwise noted)
Several explosions have been documented from May 91 vent since the 28-29 August fieldwork. The first occurred on 29 August at 2132, shortly after geologists left the island. A second, observed by R. Fleming on 5 September at 1149, produced a 2-km eruption column. Blocks larger than 1 m across fell 250 m SE of the vent and floating scoriae washed onto the shore at Crater Bay, roughly 800 m SE. A large eruption column that rose to 4-5 km altitude on 16 September at 1630, accompanied by intermittent block ejection, was observed from a nearby boat and from ~50 km away on the North Island coast (at Whakatane). Emission of ash continued overnight, with ash falling on a boat off the SE tip of the island, but tephra emission declined the next morning. Another eruptive episode was reported on 18 September at 1625, lasting 5-6 minutes and feeding a 2-km column.
When geologists returned to the island on 9 October, lithic blocks occupied scattered impact craters in a zone extending roughly 400-750 m SE from May 91 vent. Closer to the vent, blocks and craters became more common and fragments of slaggy scoria began to appear. Most of the scoriae were highly vesicular, but bombs of denser scoria, characterized by a smaller range of vesicle sizes (most <5 mm), were also found. Bombs reached 0.8 m in size and the largest observed lithic block was 1.3 m across. Most of the ballistic ejecta appeared to have fallen on the S side of the main crater floor, where it seemed to be directed by the vent configuration. Between 5 and 10 mm of fine gray ash was found at sites roughly 250 and 400 m SE of the vent, thickening toward the rim of the 1978/91 Crater complex.
Activity at May 91 vent on 9 October was similar to but less intense than that observed in late August, with emission of pink fume accompanied by loud roaring and occasional sharp detonations. The noises suggested that the top of the magma column was deeper in the conduit than at the end of August. Shock waves were visible about once a minute, less often than in late August, although conditions were less suitable for their observation. Low-pressure white gas emission from TV1 vent, roughly 50 m SE of May 91 vent, was similar to that of August, although its N wall had apparently migrated outwards 10-20 m by collapse. Voluminous gas emission continued from Noisy Nellie fumarole, on the main crater floor NE of the 1978/91 Crater complex.
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: I. Nairn and B. Scott, DSIR Geology & Geophysics, Rotorua.