Report on White Island (New Zealand) — 27 April-3 May 2016
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 27 April-3 May 2016
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2016. Report on White Island (New Zealand). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 27 April-3 May 2016. Smithsonian Institution and US Geological Survey.
37.52°S, 177.18°E; summit elev. 321 m
All times are local (unless otherwise noted)
GeoNet reported that an eruption at White Island at 2150 on 27 April was inferred by a combination of data that included the seismic network and a MetService rain radar image. The Volcanic Alert Level was raised from 1 to 3 (Minor Volcanic Eruption) and the Aviation Colour Code was raised from Green to Orange. Seismicity returned to normal levels shortly afterwards. During an overflight the next day volcanologists noted that ash deposits covered about 80% of the floor of Main Crater and continued up the N and S parts of the crater walls. Ash deposits were about 5 mm thick in areas 500 m away from the eruption site. Seismicity remained low and gas emission levels were similar to those measured prior to the event. The Volcanic Alert Level was lowered to 2.
During an aerial inspection of the area on 29 April, volcanologists observed a new crater in the NE corner of the 1978/90 Crater Complex. Gas output was slightly elevated but within the range of measurements of long-term gas output. Analysis of the eruption deposits showed that no new lava was ejected, and was instead old strongly hydrothermally altered rock material. On 2 May the Aviation Colour Code was lowered to Yellow.
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.