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Chaitén bulletin no. 105 (1 September 2009) 15 September 2009

Posted by admin in activity reports, Chaitén, Chile, eruptions.
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SERNAGEOMIN bulletin no. 105 on the Chaitén eruption, covering the period 20-31 August 2009, has been published on the website of the Argentinian state geology service SEGEMAR. Click here to see the original document (PDF). This bulletin is not yet available directly from SERNAGEOMIN. Dome growth continues, with local collapses producing debris flows, and there is a slight rise in seismicity compared to the previous bulletin. Translation as follows.

[Thanks to Werner Luis for letting me know about the appearance of this bulletin.]

20-31 August 2009

1. Visual monitoring

The images observed through the DGAC camera located in Chaitén to the south of the volcano show that the eruption continues in unchanging form with its column of gas and ash, which occasionally reaches up to 1.5 km above the dome complex. Block and ash flows still continue, indicating that the dome complex continues its growth, particularly towards the western area of the caldera.

2. Seismic activity

Between 20 and 31 August the Chaitén seismological monitoring network registered the following seismicity:

Earthquake type Average Total Magnitude RSAM
Hybrid HB 25 daily 297 Max. 4.1 Min. 1.5 ≤140,000 units

The majority of the seismicity presents very similar wave forms, which suggests that they originate from the same source and are caused by the same mechanism of origin.

3. Conclusions and interpretation

The eruptive activity continues with the growth of the dome complex, observable only on some occasions because of the winter weather. Consequently the latent danger of collapse because of the growth of the domes continues, with possible explosions and generation of block-and-ash flows, which may affect the valleys adjacent to the volcano. Moreover, the quantity of pyroclastic material from fallen volcanic rock originating from both block-and-ash flows and lateral explosions has formed important accumulations in the adjacent valleys and especially towards the valley of the Chaitén river, from which the fresh occurrence of lahars towards Chaitén during torrential rains cannot be ruled out. In consequence, given that the seismic activity remains elevated – a result of the growth of the dome complex – and the eruptive activity continues with the possibility of the generation of block-and-ash flows in random directions which may affect the surrounding valleys including the generation of new lahars, SERNAGEOMIN suggests maintaining Volcanic Red Alert.


[End of SERNAGEOMIN bulletin.]

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

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

The Volcanism Blog