Report on Ruapehu (New Zealand) — June 1980
Scientific Event Alert Network Bulletin, vol. 5, no. 6 (June 1980)
Managing Editor: David Squires.
Ruapehu (New Zealand) Activity declines
Please cite this report as:
Global Volcanism Program, 1980. Report on Ruapehu (New Zealand). In: Squires, D. (ed.), Scientific Event Alert Network Bulletin, 5:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198006-241100.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
NZGS personnel observed reduced activity during a 1.5-hour visit on 30 May. Upwelling in Crater Lake had been continuous and fairly vigorous when visited from mid-February through mid-April, and intermittent on 7 May. However, upwelling was not evident on 30 May, although faint yellow sulfur slicks were visible near the center of the lake. The water temperature near the lake outlet was 31°C, 7.5° lower than 22 days earlier. The small explosions through the lake that had occurred intermittently in previous months were not observed on 30 May, and there was no ash on snow surrounding the lake. Tiltmeters recorded 4 µrad of deflation since 13 April, in contrast to <1 µrad of change 12 February-13 April.
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 110 km3 dominantly andesitic 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, 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 3000 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.
Information Contacts: P. Otway, NZGS, Wairakei.