SERNAGEOMIN bulletin no. 108 on the Chaitén eruption, covering the period 1-15 October 2009, has been published and can be accessed (PDF) via the SEGEMAR website. A shortened version can be found on the SERNAGEOMIN website. Translation of the complete document as follows:

CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 108
1-15 OCTOBER 2009
OVDAS-SERNAGEOMIN

1. Visual monitoring

During most of the period covered by this bulletin, the volcano has remained covered by cloud. Occasonally images captured by the DGAC camera have allowed observation of columns of gases and ash emerging from the dome complex (Fig. 1, A).

SERNAGEOMIN-OVDAS personnel in the field confirm the growth of the domes and continual degasification with two important concentrations: one in the centre of the volcano, enriched with water vapour and ash) and the other towards the east of the volcano (predominantly water vapour); equally, numerous minor emissions are visible located on the volcanic edifice.

On the other hand, on 14 October at midday a vigorous explosion of the ‘piston type’ was generated: that is to say, a dense vertical projection of ash accompanied by a dispersion of particulate material forming a large cloud towards the west (Fig. 1; B to E).

Fig. 1. (A) Images from the DGAC camera, showing emissions of gases and ash. (B-E) Sequence of the ‘piston’ type explosion, occurring at midday on 14 October.

2. Seismic activity

In the process of increasing the monitoring network, currently in progress, a seismological station has been installed 1.5 km from the principal crater, located on the edge of the caldera, and there is a choice of seven sites for future stations which will complement with a high level of detail the monitoring of the activity of Chaitén volcano.

The seismicity recorded by the Chaitén volcano network has remained stable, showing a predominance of hybrid (HB) type earthquakes, with an average that has not exceeded 12 earthquakes per hour and with local magnitudes calculated as situated within the range 1.0 to 4.1. It is notable that there were fewer than 1-2 earthquakes per hour with magnitudes of more than 3.5.

3. Conclusions and interpretation

The preceding information indicates a ‘usual’ behaviour within the eruptive cycle of the volcano, indicating that the eruptive activity continues with the growth of the dome complex and the occurrence of possible ‘piston’ type explosions.

On the other hand, the quantity of pyroclastic material both from rock falls and emitted by the block-and-ash flows and lateral explosions has created large accumulations in the adjacent valleys and particularly the valley of the Chaitén river, so that the occurrence of lahars towards Chaitén during periods of intense rain cannot be ruled out.

In consequence, given that the seismicity remains at elevated levels – an effect of the growth of the dome complex – and that the eruptive activity continues with the possibility of the generation of block-and-ash flows in random directions, which may affect surrounding valleys with the generation of new lahars, SERNAGEOMIN suggests maintaining Volcanic Red Alert.

OVDAS-SERNAGEOMIN
16 October 2009

[End of SERNAGEOMIN bulletin.]

For all our Chaitén coverage: Chaitén « The Volcanism Blog.

Information
Global Volcanism Program: Chaitén – summary information for Chaitén (1508-41)
SERNAGEOMIN – Servicio Nacional de Geología y Minería (Spanish)
Erupción del Volcán Chaitén – extensive coverage of the Chaitén eruption