SERNAGEOMIN reported that during 25 November-15 December gas-and-steam plumes with variable amounts of ash rose from Chaitén to altitudes of 2.6-3.1 km (8,500-10,200 ft) a.s.l. and drifted E. Intense gas emissions came from the S flank of the first new lava dome (Dome 1), and from the NE part of the second new dome (Dome 2). On 4 December ash ejections originated from the WNW area of the dome complex. Ash plumes rose from Dome 2 to an altitude of 3.6 km (11,800 ft) a.s.l. and drifted W.
An overflight on 6 December revealed that the old lava dome was almost completely covered by Dome 1 (reddish to brown in color). Most of the eruptive activity was concentrated at the site of Dome 2, NE of Dome 1. Dome 2 was grayish in color and exhibited pinnacles and a very uneven top. Constant rockfalls originated from the slopes. Gravitational collapses of the spines produced block-and-ash flows that traveled N, NW, and S, and towards the contact area of the two domes. Domes 1 and 2 both exceeded the height of the caldera rim; Dome 1 was about 250 m above the N rim of the caldera, and Dome 2 was about 350 m above the rim. During 9-15 December, Dome 2 continued to grow rapidly and generate block-and-ash flows. The Alert Level remained at Red.
Based on observations of satellite imagery and web camera views, the Buenos Aires VAAC reported that during 10-11 and 13-14 December ash and steam plumes continuously rose to altitudes 1.8-2.4 km (6,000-8,000 ft) a.s.l. and drifted E, NE, N, and NW. Thermal anomalies were detected on satellite imagery on 10 and 14 December.
Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Buenos Aires Volcanic Ash Advisory Center (VAAC) - “Reports provided courtesy of the Smithsonian’s Global Volcanism Program and the US Geological Survey’s Volcano Hazards Program.”