Chaitén update, 21 January 2009 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

Chaiten update, 15 January 2009 15 January 2009

The latest SERNAGEOMIN bulletin on Chaitén, no. 69, covering the period 4 to 12 January 2009, has been released and is available as a pdf on the OVDAS website.

The active dome, New Dome 2, continues to grow rapidly, although we still have no figures for those growth rates. A new smaller dome or cupola is developing at the principal point of activity, consisting of a congruence of solidified spines of lava, and the constant collapses of the steep and unstable sides of this structure produce frequent rockfalls, pyroclastic flows and ash-laden plumes. It is notable that SERNAGEOMIN reports an increase in seismicity during the period of this bulletin, signalling a renewed injection of the viscous lava which feeds the dome growth. Fresh upwellings of lava, increasing the pressure beneath the unstable dome, have the potential to produce explosive collapse on a larger scale than anything we have so far seen, generating pyroclastic flows with sufficient energy to sweep through the Chaitén river valley as far as the sea. If any new lava injections are insufficient to bring about a collapse on this scale, the present steady-state situation of ongoing dome growth and constant minor collapses may continue.

Chaitén currently presents a complex, finely-balanced situation that makes forecasts very difficult, and sure enough SERNAGEOMIN makes no forecasts in this bulletin. Translation as follows.

ERUPTION OF CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 69
4 TO 12 JANUARY 2009
OVDAS-SERNAGEOMIN

1. Visual monitoring

On an overflight conducted on 9 January it could clearly be seen that the dome has grown so as entirely to fill the interior of the 3km-diameter caldera of Chaitén (Fig. 1). In addition, its principal activity has been concentrated in the southern part of New Dome 2, that is to say, in the centre of the dome complex, where an elevated cupola formed by pinnacles of lava can be seen (Fig. 1), the frequent collapses of which, caused by its instability, generate block and ash flows (Figs. 2 and 3).

Figure 1. The new domes 1 and 2 occupy the whole of the interior of the 3km-diameter caldera of Chaitén on 9 January and the principal activity was concentrated in the southern part of New Dome 2 where a cupola of solidified pinnacles of lava can be seen (red arrow).

Figures 2 and 3. Photographs taken by the DGAC camera in the afternoon of 9 January where the generation of block and ash flows caused by collapses of lava pinnacles and the formation of a cloud of reddish-brown particulate matter can be seen.

2. Seismic activity

The seismicity registered in the area of Chaitén volcano during this period has shown a significant increase both in the number of HB-type earthquakes and in the energy of some of these. The seismograms of 12 January showed a recurrence of 5-10 earthquakes per hour and, in addition, every 1-2 hours a notable HB-type earthquake of a magnitude reaching 4.0. Figure 4 shows seismograms from the STAB station, where the increase in number and amplitude (energy) of the HB-type earthquakes on 12 January, compared with the seismograms of 3 January, can clearly be seen. Among these there were occasional VT-type earthquakes of magnitudes less than 1.0.

With the data provided by the PUMA and STAB stations, it has been possible to locate, in preliminary form, the HB-type earthquakes around and beneath the caldera of Chaitén volcano.

Figure 4 (below). Seismograms from the STAB station for 3 January (top) and 12 January (bottom). A significant increase in seismicity in the Chaitén area can be seen, both in the number and the energy of some of the HB-type earthquakes during the last few days.

3. Conclusions and interpretation

The seismic activity associated with the eruption of Chaitén volcano has increased both in the number of HB-type earthquakes and the energy of some of those earthquakes, which is directly related to a large extrusion of viscous lava, accelerating the growth of New Dome 2. In turn, this growth produces sharp pinnacles which, together, have formed a steep cupola with high unstable sides, generating block and ash flows which, very possibly, will become more frequent.

In consequence, keeping in mind the persistence of the seismic activity associated with the growth of the erupting dome, with the 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)
ONEMI, Oficina Nacional de Emergencia – Chilean government emergencies office (Spanish)
SERNAGEOMIN – Servicio Nacional de Geología y Minería (Spanish)
Erupción del Volcán Chaitén – extensive coverage of the Chaitén eruption