Report on Ruapehu (New Zealand) — 9 January-15 January 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 January-15 January 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Ruapehu (New Zealand). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 9 January-15 January 2002. Smithsonian Institution and US Geological Survey.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
On 11 and 12 January steam plumes were emitted from Ruapehu. This activity was believed to be associated with hydrothermal activity in the crater lake. Prior to the steam emissions, measurements taken on 8 December revealed that the lake water temperature was at 36-38°C and that it had been heating since late November 2001. Evidence of convection was observed at the S-central vent area including minor sulfur slicks, upwelling, and light steaming. Only minor volcanic tremor was recorded at Ruapehu. The volcano remained at Alert Level 1 ("Initial signs of possible 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 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.