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Chaitén bulletin no. 89 (21 April 2009) 2 May 2009

Posted by admin in activity reports, Chaitén, Chile, eruptions.
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It’s been a long time coming, but SERNAGEOMIN have now published their full bulletin no. 89 (PDF), covering the period 15-21 April 2009, on the ‘informes’ section of the OVDAS website. A summary of the report was made available on 23 April at the SERNAGEOMIN website, and we have already provided a translation. What follows in this post is a translation of the full document.

15-21 APRIL 2009

1. Visual monitoring

During the period of this bulletin the volcano has remained obscured and only on a couple of days (18 and 19 April) has it been possible to observe the dome complex and its gas and ash column. Ther eruption continues unchanging, with the column of gas and ash permanently present, with an altitude which does not exceed 1.5 km above the domes. Depending on the meteorological conditions (humidity, temperature and winds) the column and plume has shown more condensation of water vapour (April 18) or only gas and ash, as on 19 April.

Figs 1 and 2.
Figs. 1 and 2. Views from the DGAC camera at Chaitén on 18 and 19 April, respectively, where the high condensation of water vapour on the 18th and the predominance of ash and gas on the 19th can be seen.

2. Seismic activity

The seismicity registered by the monitoring network of Chaitén volcano has declined slightly in relation to the increase reported from 8 April 2009. However, although the number of HB-type [hybrid] earthquakes has declined to 16-12 events per day, the magnitude of these has been maintained, reaching on some occasions magnitude 4.5. In relation to their eipicentres, these continue to be located on the north-west flank of the volcano, with depths that are mainly between 1 and 10 km. The seismic energy released (RSAM) has remained relatively constant, with elevated values that vary between 80000 and 120000 units (Fig. 3).

Fig 3 (click to enlarge).
Fig. 3. RSAM graph that shows the sudden increase in seismic energy from 11-15 April, to stabilize with elevated values between 80000 and 120000 units. [Click on image to enlarge.]

3. Conclusions and interpretation

Although the seismic activity reported to date has shown a slight decline in the number of HB-type [hybrid] earthquakes, it has remained relatively constant, with earthquakes that have reached magnitude 4.5. Consistent with the reported seismicity, the seismic energy released RSAM has also maintained its elevated values, a phenomenon that is related to the rate of lava emission, which is increasing the growth of the domes. This situation favours potential collapses of the domes, possible explosions and the generation of block-and-ash flows, which may affect the valleys adjacent to Chaitén volcano. Moreover, there is still the danger of lahars being generated.

In consequence, given that the eruptive process continues to develop, SERNAGEOMIN mantains 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