Report on Ruapehu (New Zealand) — May 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 5 (May 1992)
Managing Editor: Lindsay McClelland.
Ruapehu (New Zealand) Thermal activity but no phreatic eruptions from Crater Lake
Please cite this report as:
Global Volcanism Program, 1992. Report on Ruapehu (New Zealand). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 17:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199205-241100.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
The lake's temperature, measured during fieldwork on 6 May, had risen slightly to 34.5°C, but there was no evidence of further phreatic activity. Moderate upwelling over the N vents produced yellow slicks in the moderately steaming, battleship-gray lake. No upwelling from the central vent was visible. EDM data showed continued minor inflation across the lake.
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, DSIR Wairakei.