Report on Whakaari/White Island (New Zealand) — 11 November-17 November 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 November-17 November 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Whakaari/White Island (New Zealand). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 11 November-17 November 2020. Smithsonian Institution and US Geological Survey.
37.52°S, 177.18°E; summit elev. 294 m
All times are local (unless otherwise noted)
Following a period of severe weather, on 11 November GeoNet reported some mainland observations of darker plumes and deposits on webcams; scientists conducted an overflight of Whakaari/White Island on 12 November to investigate. Aerial observations confirmed the presence of ash in the emissions, originating from the main steam vent at the back of the crater lake. An initial analysis indicated that the ash was from loose material around the vent being entrained into the gas-and-steam plumes. The Volcanic Alert Level was raised to 2 and the Aviation Color Code remained at Yellow reflecting greater unrest at the surface.
There was no notable change in the location and size of active vents, though rainwater had created a small shallow lake on the floor of the 1978/90 Crater. A small earthquake sequence and several episodes of slightly increased volcanic tremor were recorded the previous week; the seismic data and observations were unusual for the volcano and may be coincident with the ash in the plume. Gas output was higher than previous recent observations; carbon dioxide flux was 2,390 tonnes/day and sulfur dioxide flux was 618 tonnes/day. The Wellington VAAC noted that the gas, steam, and ash plumes rose to1.5-1.8 km (5,000-6,000 ft) a.s.l. and drifted E and SE during 12-14 November, based on satellite data, reports from pilots, and GeoNet.
Small amounts of ash continued to be present in emissions seen during an overflight on 16 November. Laboratory data showed that the particulates were hydrothermal minerals and old volcanic material, with no fresh magmatic ash signatures. Carbon dioxide flux was 1,937 tonnes/day and sulfur dioxide flux was 710 tonnes/day, overall slightly lower than the previous measurement but still above background levels. Seismicity remained similar to the previous week, characterized by a sequence of small earthquakes, a larger than normal volcanic earthquake located close to the volcano, and ongoing low-level volcanic tremor. Re-suspended ash to 460 m (1,500 ft) a.s.l. that drifted E and NE was reported by the VAAC during 16-17 November.
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.