Report on Ruapehu (New Zealand) — July 2001
Bulletin of the Global Volcanism Network, vol. 26, no. 7 (July 2001)
Managing Editor: Richard Wunderman.
Ruapehu (New Zealand) Tremor episode peaks on 16 February, lahars predicted for near future
Please cite this report as:
Global Volcanism Program, 2001. Report on Ruapehu (New Zealand) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 26:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200107-241100.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
Ruapehu showed no signs of volcanic unrest from the end of September 2000 (described in BGVN 25:09) until mid-January 2001, when small to moderate amounts of volcanic tremor occurred. Ruapehu continued to experience low-level seismic activity, including volcanic earthquakes, through the beginning of February 2001. In mid-February, the Institute of Geological and Nuclear Sciences (IGNS) reported several periods of moderately elevated volcanic tremor. An episode of strong volcanic tremor peaked on 16 February and was the strongest tremor recorded since the 1996 eruptions, but direct observations of the crater revealed a lack of unusual surface activity. By approximately 23 February the tremor had declined to background levels. After the tremor event in February, no eruptive activity occurred, and seismic activity continued at a low level. Ruapehu remained at Alert Level 1 (signs of volcanic unrest) throughout the time period.
According to the New Zealand Herald, Ruapehu's summit crater lake had filled at twice its normal rate over the summer of 2000, causing fears of a catastrophic mudslide in the near future. A massive lahar has been predicted within 6 years from the summer of 2002-2003, with a peak flow 50% larger than the 1953 Christmas Eve disaster that wiped out the Tangiwai rail bridge, killing 151 travelers. A $370,000 early-warning system is planned that would provide 1 hour warning of the lahar's arrival on the Desert Road and 2 hours warning of its arrival at Tangiwai.
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: Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/); The New Zealand Herald, PO Box 32, Auckland, New Zealand.