Report on Ruapehu (New Zealand) — 26 February-3 March 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 February-3 March 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Ruapehu (New Zealand). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 26 February-3 March 2020. 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 a period of increased seismicity was detected at Ruapehu during 22-23 February. The series of volcanic earthquakes began with the largest event, a M 1.3, which was followed by smaller events. The data showed that the seismicity originated from a source 3 km below the summit. The amplitude of the volcanic tremor declined during 24-28 February and then again increased around 29 February-1 March.
In response to the 22-23 February sequence, volcanologists collected lake water samples and measured gas emissions the week after. The temperature of the lake water suggested slow heating from 24 to 30 degrees Celsius. They observed upwelling of gray sediment and sulfur slicks on the surface of the water. Carbon dioxide and sulfur gas emissions had increased since last measured on 7 February. GeoNet noted that gas-flux and the increased seismicity remained within the normal ranges for Ruapehu; the Volcanic Alert Level remained at 1 (minor volcanic unrest) and the Aviation Color Code remained at Green.
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.