Report on Ruapehu (New Zealand) — 16 December-22 December 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 December-22 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, 16 December-22 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)
GeoNet reported a warming trend of the crater lake water at Ruapehu, with a high temperature of 43 degrees Celsius. During an overflight to measure gas emissions the previous week, scientists observed that the lake was a uniform gray color (suggesting it is well mixed) and some water overflow at the lake’s outlet. Gas output had increased in response to the heating cycle; the amounts of carbon dioxide (CO2) and sulfur gases (SO2 and H2S) in the plume were the largest measured in the past two decades. Short-lived pulses of volcanic tremor were coincident with gas emissions. The Volcanic Alert Level was raised to 2 and the Aviation Color Code was raised to Yellow on 21 December.
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.