Report on Ruapehu (New Zealand) — 14 March-20 March 2007
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 March-20 March 2007
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2007. Report on Ruapehu (New Zealand). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 14 March-20 March 2007. Smithsonian Institution and US Geological Survey.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
According to news articles, a "moderate" lahar from Ruapehu's crater lake traveled E down the Whangaehu River valley on 18 March and reached the sea 140 km away after a soft rock-and-ash dam was breached. The section of dam that failed was about 40 m long and 7 m high. There were no reports of injuries or major damage to infrastructure and only some flooding to farmlands at the base of the volcano. The volume of water and debris was estimated at 1.3 million cubic meters. On 19 March, IGNS confirmed a 6-m drop in the crater lake level and reported an increase in seismicity following the lahar.
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.