Report on White Island (New Zealand) — October 1982
Scientific Event Alert Network Bulletin, vol. 7, no. 10 (October 1982)
Managing Editor: Lindsay McClelland.
White Island (New Zealand) Localized inflation continues
Please cite this report as:
Global Volcanism Program, 1982. Report on White Island (New Zealand). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 7:10. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198210-241040.
37.52°S, 177.18°E; summit elev. 321 m
All times are local (unless otherwise noted)
When NZGS personnel inspected the volcano on 8 October, two months after the last visit on 31 July, they found no new tephra deposits. There has been no significant tephra accumulation on the main crater floor since January 1982, the longest interval without deposition since the eruption began in December 1976. Much of the tephra cover in the W half of the main crater, where the fumaroles are, has been subjected to intense hydrothermal alteration.
Substantial steam columns were being emitted from vents on the floor and walls of 1978 Crater, and from Donald Mound and Noisy Nellie fumaroles. The strongest fumarolic activity was on the N side of 1978 Crater, near the new collapse pit. The small green pond in the SE part of the crater was still present; in a muddy black pond N of it, there was vigorous geysering. Fumarole temperatures measured at 4 places on the main crater floor ranged from 470°C in vents with low gas pressure to 695°C in high-pressure vents near Donald Mound.
Inflation of the Donald Mound area has continued at a steady rate. The E side had risen 9 mm since 31 July, and 58 mm since 21 May 1981 (figure 8), equivalent to 500 µrad of tilt. A deflationary trend was continuing about 200 m N of the Mound. The NZGS interpreted the inflation as a possible precursor of eruptive activity in this area.
Between 5 July and 1 October the number of low-frequency (B-type) seismic events did not exceed 10/day except in early July, when it increased to 31/day on the 9th and 10th, then declined. All the low-frequency events were small. High-frequency (volcano-tectonic) events usually numbered fewer than 5/day in this period, except as shown in table 4. These events were also generally small.
|Date||Number of High-Frequency Events|
|18 Jul 1982||67|
|07 Aug 1982||9|
|15 Aug 1982||15|
|18 Aug 1982||8|
|28 Aug 1982||10|
|06 Sep 1982||11|
|14 Sep 1982||18|
Moderately high frequency volcanic tremor began about 2200 on 28 July and gradually increased in amplitude until 0800 on 30 July, when a distinct decline in amplitude was apparent; tremor ceased by 1600 that day. Wide-band earthquake sequences indicative of eruption were recorded on 9, 15, and 26 September, but no eruptions were reported. Medium-frequency volcanic earthquakes were recorded on 16, 17, and 26 July, 14 August, and 4 and 18 September. The NZGS interpreted these as possible intrusive events.
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: I. Nairn and B. Scott, NZGS, Rotorua.