The latest SERNAGEOMIN bulletin on Chaitén, no. 63, covering the period 25 November to 2 December 2008, has been released. The original document can be found, as usual, at Werner Luis’s Chaitén site (PDF). Translation as follows:

ERUPTION OF CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 63
25 NOVEMBER TO 2 DECEMBER 2008
OVDAS-SERNAGEOMIN

1. Visual monitoring

During this period gaseous emissions have been observed, with a predominance of water vapour even when occasional increases in the emission of volcanic gases have been seen, with changes in the colour of the column depending on variations in the concentration of ash. The columns of gas observed have reached heights of between 1.5 and 2.0 kilometres above the active dome (Fig. 1). On some occasions, the column has shown a darker colour, due to a greater concentration of ash. Observations carried out on Saturday 29 November revealed intense gaseous emissions at the southern flank of the dome, where viscous lava has erupted under the new dome which is currently rising on the southern remnant of the old dome (Fig. 2).

Fig. 1. Eruption column from Chaitén volcano on 29 November 2008 with volcanic gases (blue), water vapour (white) and some ash (clear brown), with an altitude of 1.5km above the erupting dome. The plume is being dispersed towards the east.

Fig. 2. On Saturday 29 November this photograph was taken from Chaitén, showing intense activity with gaseous emissions in the southern flank of the dome, towards the headwaters of the tributary of the Chaitén river.

Fig. 3. View from Chaiten, 2 December 2008 at 11:08, in which the presence of water vapour and the clear brown colour at the base of the eruption column can be seen, evidencing slight emissions of ash. Nevertheless, occasional more violent explosions occur and the column is heightened and carries a greater quantity of ash, with variable behaviour.

2. Seismic activity

The information gathered by the monitoring network shows stability when compared to the seismic situation reported in earlier bulletins, although a slight decrease in the number of events has been seen. That is to say, there is a continuing predominance of HB-type earthquakes, although their presence has been in the order of 1-2 earthquakes per hour, with magnitudes of equal to or less than 3.0M. According to the distances calculated by the online stations, these earthquakes have continued to be located under the caldera and its surroundings. On the other hand, VT-type earthquakes have also appeared, although they have been very occasional and with magnitudes of less than 1.0M.

3. Conclusions and interpretation

While seismic activity has shown a slight decline compared with the last reporting period (Technical Bulletin No. 62), the presence of HB-type earthquakes is associated with the extrusion of viscous lava and the consequent growth of the new dome, which continues to erupt freely. Accordingly, and considering that the seismic activity presents changeable behaviour, with increases and decreases in the number and type of earthquakes, and that the extrusion of lava in the new dome continues and the presence of an eruption column, SERNAGEOMIN maintains Volcanic Red Alert.

[End of bulletin.]

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 – Servicio Nacional de Geología y Minería (Spanish)
Erupción del Volcán Chaitén – extensive coverage of the Chaitén eruption