Report on Ruapehu (New Zealand) — May 1980
Scientific Event Alert Network Bulletin, vol. 5, no. 5 (May 1980)
Managing Editor: David Squires.
Ruapehu (New Zealand) Phreatic explosions end
Please cite this report as:
Global Volcanism Program, 1980. Report on Ruapehu (New Zealand). In: Squires, D. (ed.), Scientific Event Alert Network Bulletin, 5:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198005-241100.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
NZGS personnel visited Ruapehu on 7 May. Although occasional small phreatic explosions had occurred through Crater Lake during previous visits beginning in late January, no explosions were observed on 7 May. There was no ash on snow that had fallen around the summit area on 29 April.
Large, yellow-green sulfur slicks floated at the N end of the battleship-gray lake. Upwelling at the center of the lake was only intermittent, in contrast to the continuous upwelling seen during earlier visits. Lake water temperature was at 39°C at the outlet, 2° higher than on 13 April, but within the range of temperatures recorded since mid-February.
The seismometer recorded continuous low-level tremor [on 7 May, as on many other days].
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: B. McG. Simpson, NZGS, Rotorua.