Chaitén update, 21 January 2009

The latest SERNAGEOMIN bulletin on Chaitén, no. 70, covering the period 12 to 19 January 2009, has been released. The complete original report as a PDF is available via Werner Luis’s Chaitén site.

This bulletin notes a slight decline in seismicity compared with last week, and interprets this as a slowing down in the rate of lava extrusion. The dome, however, continues to grow at a rapid rate and is subject to constant collapses because of its instability. The major collapse of 19 January is reported. A dramatic picture of the towering pinnacles that now form the dome’s summit (Figure 1 below) shows clearly how rapid the extrusion rate has been, and how unstable are the results. Translation as follows.

ERUPTION OF CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 70
12 TO 19 JANUARY 2009
OVDAS-SERNAGEOMIN

1. Visual monitoring

During this period it has been possible to see the great volume and height reached by the erupting dome in the central sector, particularly on 15 January, as shown in the photograph in Fig. 1 taken with a zoom from the town of Chaitén. Moreover, through the DGAC monitoring camera in the town of Chaitén, it was possible today, 19 January, between 10:59 and 12:00, to see again a major partial collapse of the steep pinnacles that form the summit of New Dome 2 above the south-eastern flank, with the consequent generation of block and ash flows (Fig. 2).

The instability of the dome continued to generate small collapses with the formation of block and ash flows during the afternoon (16:13 hrs). In addition, the gaseous emissions show a predominance of water vapour, but occasionally there has been an increase in the concentration of volcanic gases (Fig. 1). The ashes of reddish brown colour that rises above the active dome are due to the generation of particulate material associated with the block and ash flows, that is to say, fine material from the ‘grinding’ of the viscous lava that forms the dome.

Fig. 1. Photograph taken on 15 January of the new dome with its prominent pinnacles, viewed from the south-west (courtesy Sr. C. Peréz).

Fig. 2. Photographic sequence from 19 January between 10:59 and 12:00, which shows the major partial collapse of the pinnacles on the summit of the dome towards the south-east, captured by the DGAC camera at Chaitén.

2. Seismic activity

The seismic activity recorded by the monitoring network at Chaitén volcano during this period has shown a slight decline in the number of HB-type earthquakes and in their energy. The seismograms show between 1 and 4 earthquakes per hour, within which some stand out with a maximum magnitude of up to 3.8 (Fig. 3). In addition, occasional VT-type earthquakes of less than magnitude 0.8 have been recorded.

The HB-type earthquakes continue to be located, on a preliminary basis, in the southern zone and some beneath the caldera of Chaitén volcano.

Fig 3. Seismograms from STAB station for 12 January (top) and 19 January (bottom), showing a slight decrease both in the number and the energy of some of the HB-type earthquakes in the last few days.

3. Conclusions and interpretation

The seismicity of Chaitén volcano has declined slightly, both in the number of events and in the energy released, which would indicate that the extrusion of viscous lava continues, but with a growth dynamic less rapid than that shown last week.

The accelerated growth of the last period generated a condition of high instability in the summit pinnacles and the flanks of the dome, producing the partial collapse processes of 19 January. Meanwhile the growth of the dome continues, which may generate new collapses which, eventually, may affect the heads of the main valleys.

In consequence, mindful of the continuing seismic activity associated with the growth of the erupting dome, with the consequent generation of block and ash flows, SERNAGEOMIN maintains Volcanic Red Alert.

[End of 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