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Chaitén bulletin no. 83 (9 March 2009) 11 March 2009

Posted by admin in activity reports, Chaitén, Chile, eruptions.
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Bulletin no. 83 on the eruption of Chaitén volcano, covering the period 4 to 9 March 2009 , has been released by the Chilean geological service SERNAGEOMIN. The original document (PDF) can be found on Werner Luis’s Chaitén site. Translation as follows.

4 TO 9 MARCH 2009

1. Visual monitoring

During this period the growth of the dome complex has continued, concentrated particularly in the central-southern sector, where the central pinnacle and a significant remaining portion of Dome 1 are located. The images taken by the DGAC camera have shown frequent collapses that have occurred especially on the unstable sides of the central pinnacle and the south wall of Dome 1. All the gravitational collapses have produced block-and-ash flows and some of these have been channelled towards the headwaters of the Chaitén river. The fine particulate material of pulverized rock from the block-and-ash flows (the ‘ash’) has risen with the volcanic gases and water vapour, forming plumes of light brown colouring, which have tended to disperse in a south-eastern direction towards Futaleufú. Today [i.e. 9 March 2009], collapses have been produced towards the south with winds predominantly from the north, which has dispersed the particulate material in the direction of Chaitén (Fig. 1).

Figure 1.
Figure 1. Gravitational collapse of the south flank of Dome 1 recorded at 16:10 on 9 March 2009 by the DGAC camera, in which the dispersal of the plume of fine material towards Chaitén can be clearly seen.

2. Seismic activity

The analysis of the data obtained by the Chaitén volcano monitoring stations reveals that the seismic activity has slightly declined in the number of HB-type [Hybrid] earthquakes occurring, with 1 earthquake every 2-3 hours, with a magnitude over 3.5, some of which reached a magnitude 4.0 (Fig. 2).

With regard to the VT-type [volcano-tectonic] earthquakes, these have practically disappeared, with only 2 earthquakes of very low magnitude of less than 1 being recorded.

In general, the HB-type earthquakes are located to the south of the Chaitén caldera (Fig. 3), with depths of around 5.0km.

Figure 2.
Figure 2. Seismogram recorded at STAB station for 7 March between 00:00 and 11:59 GMT. The average occurrence of HB-type earthquakes with magnitudes between 3.5 and 4.0 is 1 earthquake every 2-3 hours (red ellipse).

Figure 3.
Figure 3. Location of earthquakes on 7-8 March. They are located to the south of the Chaitén caldera. [Click on picture for enlarged version.]

3. Conclusions and interpretations

The seismic activity of Chaitén volcano continues to decline slightly in the number of larger HB-type earthquakes, that is, those with magnitudes between 3.5 and 4.0. The earthquakes that have been recorded have principally been of HB-type, which indicates the continuing feeding of magma into the dome complex, principally in the central-southern sector.

With regard to possible scenarios, these remain as outlined in the previous report, that is to say, total or partial gravitational collapses of the remaining section of Dome 1 towards the south and/or major collapses during periods of intense rainfall, the block-and-ash flows could produce hot lahars in the directon of Chaitén, while the large quantity of volcanic material and tree trunks in the valley of the Chaitén river could subsequently be removed towards the town of Chaitén producing new lahars.

Taking into account the continuing seismic activity with HB-type earthquakes of up to magnitude 4.0, the continuing growth of the dome complex and the frequent gravitational collapses from the southern part of Dome 1 and from the central pinnacle, associated with explosions and pyroclastic flows, along with the high probability of the occurrence of new lahars during periods of intense rainfall, SERNAGEOMIN maintains 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