Chaitén update, 4 January 2009 4 January 2009

Chaitén volcano in southern Chile is still erupting, eight months after bursting into life on 2 May 2008. The latest Chaitén bulletin from SERNAGEOMIN, no. 67 covering 24-29 December 2008, was issued on 31 December, and the original can be accessed via the OVDAS site (PDF). A shortened version, combined with a report on Llaima (more on Llaima here tomorrow, by the way), can also be found on the SERNAGEOMIN website. Translation as follows.

ERUPTION OF CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 67
24-29 DECEMBER 2008
OVDAS-SERNAGEOMIN

1. Visual monitoring

During most of the period covered by this bulletin, cloud cover in the area has prevented observation of the eruption column of Chaitén volcano on a continuous basis.

On 25 and 28 December, via the DGAC camera, it was possible to see a column of gases, water vapour and some fine particulate material (brown colour) about 2km above the erupting New Dome 2. At the base of the column a greater concentration of particulate material could be seen because of the frequent occurrence of collapses of New Dome 2 and the generation of block and ash flows (Fig. 1).

Figure 1. Image obtained from the DGAC camera on 25 December. At the base of the eruption column and in the plume fine particulate material can be seen (brown colour).

2. Seismic activity

The seismicity registered by the monitoring stations in the area of Chaitén volcano has remained stable. In the signals recorded, HB-type earthquakes have predominated with a periodicity of 2-6 earthquakes per hour, with 1-2 earthquakes reaching magnitude 3.8 among them (Fig. 2).

According to S-P seismic wave calculations for the hybrid- (HB-) type earthquakes, these have continued to be located in the interior and the surroundings of the caldera.

Additionally, there have been infrequent VT-type earthquakes with magnitudes of less than 1.0.

Figure 2. Seismogram from STAB station, representing 27 and 28 December. In the adjoining figure is the seismogram of the HB-type earthquake which reached magnitude 3.8 (orange ellipse).

3. Conclusions and interpretation

Seismicity has remained stable during the last two weeks. Analysis of the data has related this to the continuing extrusion of viscous lava from New Dome 2 which continues to erupt. This can be related to frequent collapses of New Dome 2, the volume and rapid growth of which produces a striking instability in its sides and top. Nor can the occurrence of phreatomagmatic explosions or lateral explosions from the erupting dome be ruled out. In consequence, given that the seismic activity persists and is associated with the growth of New Dome 2 in eruption, SERNAGEOMIN maintains Volcanic Red Alert.

[End of bulletin.]

Info courtesy of The Volcanism Blog @

http://volcanism.wordpress.com/2009/01/04/chaiten-update-4-january-2009/
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