Report on Ruapehu (New Zealand) — 4 October-10 October 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 4 October-10 October 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Ruapehu (New Zealand). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 4 October-10 October 2006. Smithsonian Institution and US Geological Survey.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
A M 2.8 earthquake centered at Ruapehu was recorded on 4 October. Scientists visited the summit crater lake on 7 October and confirmed that a small hydrothermal eruption had occurred. The lake water level had risen 1 m since a previous measurement, and evidence suggested wave action up to 4-5 m above the surface of the lake. The lake temperature was 22.5°C, up from 15°C. Ruapehu remained at Volcanic Alert Level 1 (some signs of volcano unrest).
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.