Report on Ruapehu (New Zealand) — May 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 5 (May 1987)
Managing Editor: Lindsay McClelland.
Ruapehu (New Zealand) Crater lake temperature falls; some tremor
Please cite this report as:
Global Volcanism Program, 1987. Report on Ruapehu (New Zealand). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 12:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198705-241100.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
Activity remained at a low level when geologists visited the crater on 26 May. Crater Lake temperature had fallen to 14.2°C (from 19.0°C on 15 April) although it had probably been relatively stable since early May. Minor convection occurred over the main vent. No significant deformation was recorded.
After a long period of weak seismicity, tremor began on 21 May, increasing to maximum amplitude on 24 May (<10 mm, 0-peak), then decayed almost to background by 28 May.
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.