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.
Geological Summary. 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 NW-flank Murimoto debris-avalanche deposit. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. The broad summait area and flank contain at least six vents active during the Holocene. Frequent mild-to-moderate explosive eruptions have been recorded from the Te Wai a-Moe (Crater Lake) vent, and tephra characteristics suggest that the crater lake may have formed as recently as 3,000 years ago. Lahars resulting from phreatic eruptions at the summit crater lake are a hazard to a ski area on the upper flanks and lower river valleys.
Sources: New Zealand Herald, Associated Press, GeoNet, Stuff