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Chaitén bulletin no. 87 (6 April 2009) 18 April 2009

Posted by admin in activity reports, Chaitén, Chile, eruptions.
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Bulletin no. 87 on the eruption of Chaitén volcano, dated 6 April 2009, is available in original form as a PDF via the ‘informes’ page at OVDAS (now back online after its recent problems), and a shortened version can be found on the SERNAGEOMIN website. The main points to emerge are an increase in seismicity, and that a new pinnacle is growing on the southern sector of dome 1, south of the large pinnacle that is already in situ. Translation as follows.

ERUPTION OF CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 87
30 MARCH 2009 TO 6 APRIL 2009
OVDAS-SERNAGEOMIN

1. Visual monitoring

The volcano has remained almost totally clouded and only very occasionally is it possible to observe eruptive activity through the DGAC and Canal 13 cameras in Chaitén (Fig. 1), which show that the small gravitational collapses that are affecting the central pinnacle continue, and that a new pinnacle, much smaller than the central pinnacle, appears to be growing on the southern sector of dome 1.

Figure 1
Figure 1. Images from the Canal 13 camera which indicates the continuing growth and the gravitational collapses of the central pinnacle. In addition, a new pinnacle is growing in the southern sector of dome 1. [Click on picture for enlarged version.]

2. Seismic activity

The seismic data obtained by the Chaitén volcano monitoring network shows a relative increase in the number of HB-type [hybrid] earthquakes, principally those with magnitudes of less than 3.0, which have reached an average of 7-10 earthquakes per hour. Moreover, the earthquakes of greater magnitude, that is to say those between 3.0 and 3.3, reached, in some periods, up to 10 earthquakes per day (Fig. 2). The depth of the HB-type earthquakes remains between 1-10 kilometres and they remain low [in energy] and immediately to the south of Chaitén volcano.

Figure 2
Fig. 2. Seismograms from the STAB station for 28 March (left side) and 5 April (right side). A comparison shows the increase in the number of HB-type earthquakes in the graph for 5 April. [Click on picture for enlarged version.]

3. Conclusions and interpretation

The seismic records continue to show an increase in the number of HB-type earthquakes per hour, with a maximum magnitude of 3.3. In the same way, the location and depth of the earthquakes remains unchanged. In consequence, it is suggested that the central pinnacle in the southern sector of dome 1 continues to grow, probably, at a greater rate, and that the seismicity has developed in a relatively superficial and localized form.

In consequence, given that the eruption, the seismic activity and the growth of the dome complex continue, with consequent gravitational collapses and generation of block and ash flows and the potential danger of the generation of lahars, SERNAGEOMIN maintains Volcanic Red Alert.

[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

The Volcanism Blog