Report on Ruapehu (New Zealand) — 23 December-29 December 2020
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 23 December-29 December 2020
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2020. Report on Ruapehu (New Zealand) (Sennert, S, 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.
Geological Summary. 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 NW-flank Murimoto debris-avalanche deposit. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. The broad summait area and flank contain at least six vents active during the Holocene. Frequent mild-to-moderate explosive eruptions have been recorded from the Te Wai a-Moe (Crater Lake) vent, and tephra characteristics suggest that the crater lake may have formed as recently as 3,000 years ago. Lahars resulting from phreatic eruptions at the summit crater lake are a hazard to a ski area on the upper flanks and lower river valleys.