Chaitén bulletin no. 104 (21 August 2009)

A mere two weeks after it was issued, SERNAGEOMIN bulletin no. 104 on the Chaitén eruption, covering the period 4-20 August 2009, has been made available to the public – not by SERNAGEOMIN itself but via the website of the Argentinian state geology service SEGEMAR. Click here to see the original document (PDF). Translation as follows.

CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 104
4-20 August 2009
OVDAS-SERNAGEOMIN

1. Visual monitoring

Personnel from the Observatorio Volcanológico de Los Andes del Sur (OVDAS) in the area were able to observe that the activity continues, shown by the column of gases, water vapour and ash, occasionally reaching up to 1.5 km above the dome complex; in addition, 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. 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

The Chaitén seismological monitoring network registered the following seismicity:

Earthquake type	Average	Total	Magnitude		RSAM
Hybrid HB	16 daily	260	Max. 4.1	Min. 1.9	<150,000 units

The majority of the seismicity presents very similar wave forms, which suggests that they originate in 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, only observable on some occasions because of the winter weather; 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 Chaitén 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 as a result of the growth of the dome complex, with the possibility of the generation of block-and-ash flows which may affect the surrounding valleys including the generation of new lahars, SERNAGEOMIN maintains Volcanic Red Alert.

OVDAS-SERNAGEOMIN
21.08.09

[End of SERNAGEOMIN bulletin.]

Yet another ‘informe’ that does not inform. Where are the photographs, the detailed figures on seismicity, the descriptions of the volcano’s eruptive activity that go beyond reporting that it ‘continues’? Where are the data on the estimated volume and current rate of growth of Chaitén’s prodigious dome? We don’t get any of that. We do, however, get one innovation: a very basic table under ‘seismic activity’, enabling SERNAGEOMIN to achieve a net saving of approximately 40 words. If the current trend towards minimizing the content of these bulletins continues, SERNAGEOMIN will shortly be issuing blank sheets of paper.

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