Report on Ruapehu (New Zealand) — October 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 10 (October 1986)
Managing Editor: Lindsay McClelland.
Ruapehu (New Zealand) Crater Lake temperature increases from July low
Please cite this report as:
Global Volcanism Program, 1986. Report on Ruapehu (New Zealand) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:10. Smithsonian Institution.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
Crater Lake temperature had increased to 23°C by 15 October ... . Upwelling over the main vent was first observed 15 October, while upwelling over the N vent was continuous since early September. Rapid oscillations of 2-7 cm in lake level were observed on 15 October, but there were no high surges, ash deposits, or other evidence of eruptions. Sulfur emissions were at background levels and lake color has remained battleship gray. The 15 October deformation data showed no significant changes since the July and August surveys.
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.
Information Contacts: P. Otway, NZGS Wairakei.