Report on Ruapehu (New Zealand) — October 1997
Bulletin of the Global Volcanism Network, vol. 22, no. 10 (October 1997)
Managing Editor: Richard Wunderman.
Ruapehu (New Zealand) Seismic and volcanic activity decline in late October
Please cite this report as:
Global Volcanism Program, 1997. Report on Ruapehu (New Zealand) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 22:10. Smithsonian Institution.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
The increased seismic and volcanic activity that began on 2 October (BGVN 22:09) had returned to low levels early on 14 October after sporadic small eruptions of mud and rocks on the 12th. Activity continued to decline during the second half of the month. By 31 October the volcanic alert status had been reduced from Level 2 (minor eruptive activity) to Level 1 (signs of volcano unrest) with volcanic tremor remaining above typical background level. The last small eruption, accompanied by a volcanic earthquake, occurred at 2120 on 18 October. There was no geysering or big disturbances on the crater lake surface during the last week of October. The lake temperature in late October was 52-55°C and the water color was light gray. Scientists observed small radial wave patterns on the surface, indicating fluctuating water levels. The N portion of the crater floor was dry and a prominent area of gas and steam vents (fumaroles) had developed in the NW part.
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: Brad Scott, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: https://www.gns.cri.nz/).