The Chilean Servicio Nacional de Geología y Minería (SERNAGEOMIN) has issued a new bulletin today, 13 May 2008, regarding the ongoing eruption at Chaitén volcano.

Yesterday, 12 May, SERNAGEOMIN carried out overflights and assessed the height of the eruption column as 8 kilometres above sea level. During the overflight ‘at least four explosions were observed that generated columns of a similar height, which were carried to the north-east by the prevailing strong (80-100 km/hr) south-west winds’. The overflight also revealed several acres of burned forest on the northern flank of the caldera ‘due to minor pyroclastic flows generated by the collapse of the base of the eruptive column and/or lateral explosions around the crater’, while areas to the north-east ‘have also been severely affected by small pyroclastic flows and the forests entirely levelled and burned’. The overflight also provided more information on the condition of the Chaitén lava dome:

The central dome presented a thick vertical column of gas and ashes from a crater of about 1 km diameter, located on the northern flank of the dome and extending towards the top. Western and north-western areas show the traces of many minor pyroclastic flows on their flanks, which have burned all vegetation inside the caldera, and even beyond its northern edges.

The overflight investigated the flooding of the Río Chaitén (also known as the Río Blanco) in Chaitén town yesterday and confirmed that the cause was ‘the large volumes of ash and pumice’ being carried by the river … the channel has been filled in by volcanic sediment’:

This process resulted from the accumulation of large amounts of ash and pumice in the headwaters of the Río Chaitén, which rises in the caldera of the volcano of the same name. The deposition of this material into the river will have caused the mud flow (lahar), a process that will recur, especially if there are heavy rains during the next few days.

The bulletin reports an increase in the number of VT seismic events around the volcano over the last 36 hours, and swarms of minor earthquakes have been recorded at intervals not exceeding 5 minutes.

The continuing concern for SERNAGEOMIN is ’possible future explosions causing the total destruction of the dome and the generation of large pyroclastic flows by the collapse of the eruption column, which would descend radially from the volcano through the adjacent valleys’. This highly destructive outcome is the worst-case scenario about which SERNAGEOMIN volcanologists and others have been warning for the last ten days: it remains a very real possibility.

For all our Chaitén coverage: Chaitén << The Volcanism Blog

Information
Global Volcanism Program: Chaitén - summary information for Chaitén (1508-41)
ONEMI, Oficina Nacional de Emergencia - Chilean government emergencies office (Spanish)
SERNAGEOMIN - volcanology information from the Servicio Nacional de Geología y Minería, Chile (Spanish)