Report on Ruapehu (New Zealand) — 23 December-29 December 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 23 December-29 December 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Ruapehu (New Zealand). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 23 December-29 December 2020. Smithsonian Institution and US Geological Survey.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
On 28 December GeoNet reported that during the previous week the temperature of Ruapehu’s crater lake water slightly decreased from 43 to 41 degrees Celsius. Moderate-to-strong levels of volcanic tremor were recorded along with a small number of shallow volcanic earthquakes. The largest volcanic earthquake was an M 2.2 (on 26 December) which was uncommonly large, and combined with elevated tremor indicated ongoing unrest. The Volcanic Alert Level remained at 2 and the Aviation Color Code remained at Yellow.
Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The dominantly andesitic 110 km3 volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake (Te Wai a-moe), is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3,000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.