Based on observations of satellite imagery, SIGMET reports, and pilot reports, the Buenos Aires VAAC reported that during 7-13 May ash plumes from Chaitén were continuously present and during 7-9 May rose to altitudes of 6.1-10.1 km (20,000-33,000 ft) a.s.l. The plumes drifted E and NE.
SERNAGEOMIN reported that on 7 May, seismicity from Chaitén increased and a large explosion was registered. On 8 May small pyroclastic flows traveled E and contacted the Rayas River, possibly causing steam plumes. During a break in the cloud cover, the ash-and-gas plume, present since 2 May, was seen rising to an altitude of 15.1 km (50,000 ft) a.s.l. and drifting NE. The W side of the plume was darker and denser. ONEMI (Oficina Nacional de Emergencia – Ministerio del Interior) reported ashfall in multiple areas on 7, 8, and 10 May.
On 12 May, the plume rose to an altitude of 8 km (26,200 ft) a.s.l. During an overflight conducted by SERNAGEOMIN, four more plumes of a similar altitude were generated by explosions and drifted NE. Several hectares of burned vegetation, likely from pyroclastic flows or lateral explosions, were noted on the N flank of the dome. Small pyroclastic flows may also have been responsible for completely burned forest to areas in the NE, and on the W and NW dome flanks. A lahar caused the banks of the Chaitén River to overflow about 200 m on each side, damaging about 40 houses and numerous cars that were partially or fully submerged. During an overflight on 13 May, evidence of pyroclastic flows on the N flank was observed. An ash-and-gas plume emitted from the lava dome drifted NE. The Alert Level remained at Red.
Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Oficina Nacional de Emergencia – Ministerio del Interior (ONEMI), Buenos Aires Volcanic Ash Advisory Center (VAAC) – “Report provided courtesy of the Smithsonian’s Global Volcanism Program and the US Geological Survey’s Volcano Hazards Program.”