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Chaitén bulletin no. 93 (19 May 2009) 5 June 2009

Posted by admin in activity reports, Chaitén, Chile, eruptions.
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Bulletin no. 93 on the eruption of Chaitén volcano, covering the period 12-19 May 2009, is now available as a PDF via the informes page of the Observatorio Volcanológico de los Andes del Sur (OVDAS) website. There is also a summary version on the SERNAGEOMIN website. The elevated level of seismicity at Chaitén, now sustained for nearly two months, remains the most notable characteristic. Translation as follows.

ERUPTION OF CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 93
12-19 MAY 2009
OVDAS-SERNAGEOMIN

1. Visual monitoring

Some photographs from the DGAC camera at Chaitén show that the eruption of the volcano continues in an unchanging form, with its column of gas and ash of white to grey colouring climbing up to 1.5 km above the dome complex. Although observations have not been possible during all this period because of the adverse weather conditions, there has been a notable predominance of water vapour in the column because of the atmospheric humidity and the low temperatures, which have caused condensation. The block-and-ash flows have persisted, indicating that the dome complex has continued to grow, especially towards the south-western area of the caldera.

2. Seismic activity

The seismicity registered by the monitoring network of Chaitén volcano shows stable behaviour, although it should be emphasized that an elevated level of seismic activity has been maintained for a duration of nearly two months. The average of HB-type [hybrid] earthquakes has remained between 9 and 14 events per day, with magnitudes reaching 4.1 in some cases. With regard to the seismic energy released RSAM, this has continued to show values similar to the preceding weeks, with values that exceed 130,000 units. Moreover, it is important to note that there has been at least two groups of earthquakes originating from different sources, although [all] associated with the activity of the volcano. This has been shown by their distinct forms and the different arrival times at the [seismic] stations. The epicentres of the HB-type earthquakes of greater magnitude are located on the western edge of the caldera, with depths principally concentrated between 5 and 9 km.

3. Conclusions and interpretation

The eruptive activity continues with the sustained growth of the dome complex, which continues to rise and expand, and the generation of block-and-ash flows, which are on occasion visible from Chaitén [town]. The seismic activity occurring during the period has remained relatively stable and some of the earthquakes of greater magnitude have been slightly perceptible to people in the area. There is a continuing danger of gravitational collapses, possible explosions and the generation of block-and-ash flows, which could affect the valleys adjacent to Chaitén volcano. In consequence, given that the eruption continues, and the seismic activity associated with the sustained growth of the dome complex remains elevated, with the possibility of the generation of block-and-ash flows which may affect surrounding valleys, SERNAGEOMIN maintains Volcanic Red Alert.

OVDAS-SERNAGEOMIN
19.05.09

[End of SERNAGEOMIN bulletin.]

I am late posting this bulletin because of my absence from the blog during late May. Apologies for the delay.

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

The Volcanism Blog