Report on Ruapehu (New Zealand) — October 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 10 (October 1987)
Managing Editor: Lindsay McClelland.
Ruapehu (New Zealand) Lake temperatures fall; minor inflation
Please cite this report as:
Global Volcanism Program, 1987. Report on Ruapehu (New Zealand) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 12:10. Smithsonian Institution.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
. . . Crater Lake temperature fell. . . . to 28.5°C on 16 October. The lake was steaming and dark yellow-green (sulfur) slicks were periodically observed near the lake center. Deformation measurements indicated a minor 8 mm (inflationary) increase in crater diameter. Seismicity since 8 September has been dominated by low-amplitude 2 Hz volcanic tremor. No eruptive activity has been reported. During a visit on 28 September a geologist observed a seiche with amplitude of 50 mm and period of ~35 seconds. A similar seiche was observed on 17 October 1986.
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; B. Scott, NZGS Rotorua.