Report on White Island (New Zealand) — February 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 2 (February 1986)
Managing Editor: Lindsay McClelland.
White Island (New Zealand) New active vent produces tephra
Please cite this report as:
Global Volcanism Program, 1986. Report on White Island (New Zealand). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 11:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198602-241040.
37.52°S, 177.18°E; summit elev. 321 m
All times are local (unless otherwise noted)
Minor magmatic eruptive activity resumed ... about 1 February from a new vent within the 1978 Crater complex. On 3 February helicopter pilot Ian Johnson observed a new active vent and associated tephra fall.
About 15 low-frequency B-type earthquakes/day occurred from December into February with unusually large (50 mm p-p) amplitudes, although a gradual decline in amplitudes was apparent. Significant periods of volcanic tremor were recorded in January (11, 19, 20-21, 25-29) and February (1-5) but no vent-forming episode could be clearly recognized.
When geologists visited the volcano 10 February, there was a new vent ~ 25 m in diameter near the base of the E crater wall, farther E than any vent of the 1976-82 eruption sequence. The vent emitted vapor at a moderate rate and a small amount of very fine ash was occasionally present in the gas plume.
A fresh layer of ash, 10-15 mm thick, was on the main crater floor to 150-200 m E of the new vent and a small ejecta apron extended 30-50 m W of the vent. Small scoria bombs were sparsely scattered on the surface within 50 m of the new vent. Bombs were rarely larger than 100 mm in diameter. One had clearly flattened on impact, indicating it was still soft when it fell. The scoria is fresh, dark brown, vesiculated glassy andesite with phenocrysts of plagioclase and pyroxene. Recently deposited tephra comprise reworked crater-fill detritus, some fresh crystals, and brown glass.
Fumarole temperatures of 350-360°C were measured on 10 February, 25° cooler than on 13 November (10:11) and 15-25° cooler than on 7 February. COSPEC measurements on 7 February showed an SO2 emission rate of 570 t/d, a substantial increase over the 320 t/d detected on 21 November 1984 and 350 t/d recorded on 7 January 1985.
Geologic Background. Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the 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 summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE. Intermittent moderate phreatomagmatic and strombolian eruptions have occurred throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced 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.
Information Contacts: New Zealand Geological Survey (NZGS); P. Kyle, New Mexico Inst of Mining & Technology.