An important sector of the southern flank of the dome collapsed on Thursday 19th February, producing a lateral explosion and block and ash flows and pyroclastic flows, which descended south, reaching the top of the Chaitén river valley, 5 km north of the Chaiten town. In addition, eruptive column was erupted about 2 pm, reaching approximately 8 km high, and drifting southeast, and creating ashfall in the town of Futaleufu. Residents near the volcano indicated the ash plume may have reached 15-20 km high.
A Twin Otter overflight of Chaiten volcano on Thursday revealed the north flank of the volcano had a similar appearance to that of previous weeks. Towards the south flank of the volcano, partial observations revealed that forest had been burnt. A helicopter overflight revealed a 500 m x 500 m collapse of the summit dome, which generated pyroclastic flows that advanced by 4 to 5 km down the Chaiten river valley, destroying native forest. At a location in the valley 3-4 km from Chaiten town, there were 5 or 6 locations which emitted gas and water vapour. This process can be interpreted primarily as side effects of pyroclastic flows, which generated large amounts of steam when in contact with water.
In view of the continuing seismic activity associated with the eruption, along with growth and major collapses of the dome, lateral blast, block and ash flows and pyroclastic flows, Volcanic Red Alert remains in place for Chaiten volcano. Further block and ash flows and pyroclastic flows may affect Chaiten town and also to other sectors of the volcano. Ashfall may affect locations downwind from the volcano.
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