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Chaitén bulletin no. 90 (28 April 2009) 6 May 2009

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Bulletin no. 90 on the eruption of Chaitén volcano, covering the period 22-28 April 2009, is now available as a PDF via the informes page of the Observatorio Volcanológico de los Andes del Sur (OVDAS) website. Translation as follows.

ERUPTION OF CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 90
22-28 APRIL 2009
OVDAS-SERNAGEOMIN

1. Visual monitoring

During this period the volcano has remained mostly obscured, although on 28 April it was uncovered and it was possible to see the dome complex and its column of gas and ash (Figs. 1 and 2). The eruption has remained in an unchanging form, with a column of gas and ash (principally water vapour from condensation) which has not exceeded 1.5 km above the domes (Fig. 1). However, from the photograph in Fig. 2 it is possible to infer that the dome complex has grown until it completely fills the interior of the caldera of average 2.5 km diameter. The highest pinnacles are being formed in the western and south-western edges of the caldera (Fig. 2).

Figure 1
Figs. 1 [above] and 2 [below]. Views from Chaitén on 28 April, showing the column of ash and gas with a predominance of water vapour because of condensation (1). The complex of domes have invaded the interior of Chaitén caldera and there are prominent pinnacles on the inner rims to the west and south-west (2).
Figure 2

2. Seismic activity

The seismicity recorded by the monitoring network of Chaitén volcano has decreased slightly in relation to the increase reported from 8 April 2009. Although the number of HB-type [hybrid] earthquakes of greater magnitude has decreased slightly, from 16 to 12 units per day, the magnitudes of these have remained high, registering up to 4.5 upon occasionally. In relation to their epicentres, they remain located in the north-west flank of the volcano, with depths that are principally concentrated between 1 and 10 km. Finally, with respect to the RSAM seismic energy released, as with the seismicity, has remained relatively constant, with values that range between 80000 and 120000 units (Fig. 3).

Figure 3 (click on image to enlarge)
Fig. 3. RSAM graph showing a sudden increase in seismic energy from 11 to 15 April, which then stabilized with elevated values between 80000 and 120000 units. [Click on image to enlarge.]

3. Conclusions and interpretation

The eruption continues in the same form, with a continuing growth in the dome complex, which appear to occupy the entirety of the interior of Chaitén. Although the seismic activity reported to date has shown a slight decline in the number of HB-type earthquakes, their magnitudes have reached 4.5. Consistent with the reported seismicity, the RSAM seismic energy released has also maintained its values, a phenomenon that is related to the increase in the growth of the dome complex. In consequence, it is possible that explosions and block-and-ash flows could occur, which could affect the valleys adjacent to Chaitén volcano.

Considering that the eruptive activity continues with a high rate of growth of the domes and high seismic activity, 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

Comments

1. Fresh Bilge » Active - 6 May 2009

[…] another belated report from Chaitén, covering the period April 22-28, released by the Chilean government with its usual lethargy, and […]


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