Report on Ruapehu (New Zealand) — 29 April-5 May 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 April-5 May 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, 29 April-5 May 2020. Smithsonian Institution and US Geological Survey.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
On 4 May GeoNet reported a cooling trend of the crater lake water at Ruapehu with a current temperature of 35 degrees Celsius. During February-April the water temperature had peaked at 42 degrees Celsius. The intensity of volcanic tremor had been weak during the past month after a peak in strength in early March; tremor had declined slowly almost in conjunction with the lake water cooling trend. During a visit to the lake the previous week volcanologists noted that the lake was a uniform gray color with a few surface slicks and no obvious upwelling. Since that visit the water level had risen and was flowing into the upper Whangaehu River. 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.