Report on Ruapehu (New Zealand) — 29 April-5 May 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 April-5 May 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Ruapehu (New Zealand). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 29 April-5 May 2015. Smithsonian Institution and US Geological Survey.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
GeoNet reported that water temperatures of Ruapehu's summit Crater Lake had been increasing since early December 2014, rising from 15 degrees Celsius to over 40 degrees in late January-early February. The temperatures declined to 31 degrees in mid-March, and then climbed again to 37-39 degrees. No other changes were detected at the lake. In addition, over the previous 2-3 weeks intermittent moderate-to-strong levels of volcanic tremor were detected, which had been some of the strongest recorded there over the past eight years. The report noted that historically there had not been a direct link between volcanic tremor and discrete volcanic eruptions or sequences of eruptions. The Aviation Colour Code remained at Green and the Volcanic Alert Level remained at 1 (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 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.