The most recent Chaitén report I have received from SERNAGEOMIN is dated 30 June 2008 (not yet published on the SERNAGEOMIN site or elsewhere). Translation as follows … it’s a lengthy document with images, so I’ve put it under the cut. Click on ‘more’ to continue.

Eruption of Chaitén volcano
Thirty-second technical report, 30 June 2008

1. VISUAL OBSERVATIONS

The bad weather conditions yesterday prevented observation of the column of gas and ash. However, today, 30 June, it was possible to have visual contact both from Queilen and through the camera installed by the DGAC in the town of Chaitén (Fig. 1). In both cases it was possible to observe the eruptive column, at an estimated altitude of around 1km. The dispersion of the plume could not be observed but was probably towards the north-east, in accordance with the prevailing winds of 30 June. Indeed, a photograph provided by Mr Christian Brown (Fig. 2) shows that the dispersion was occurring towards the north-north-east. In this photograph, it is possible to see that the growth of the dome, although it has continued, has been slower in comparision to that of the month of May, when the changes in size were evident. From the south one observes a new dome totally covering the old, with boulders and snow on the slopes.

Figure 1. Picture taken by the northern camera of the Dirección General de Aeronáutica (DGAC) on 30 June at 16:11.

Figure 2. View towards the east from the western edge of the caldera. It is possible to recognize the new dome (centre), the column of gases (water vapour and ash), and the heavy ash deposits that have accumulated inside the caldera over the last two months. Photograph courtesy Christian Brown.

In some sectors there are patches of sulphur and rocky ’spines’ in the west and south-west of the new dome. In the western sector, in the bottom of the caldera-type depression, mudflow deposits can be seen, while in the southern sector dams or blockages of drainage caused by falling rocks are visible (orange arrow in Fig. 2). The emission of ash continues with less intensity, both in altitude and in the volume of material emitted.

2. SEISMIC ACTIVITY

Network faults have prevented the connection of the PILLAN station with the seismic monitoring network, and it was impossible to upload data to the OVDAS FTP site. Data delivered to the other two stations of the Chaitén volcano seismic monitoring network (PUMA and STBA) continued to show a weak increase in seismic activity.

The information contained in the previous report (thirty-first report) [see this blog post] established an upturn both in the number of earthquakes and in their associated magnitude. This increase continues in slight but sustained form: counting both yesterday and today there have been about 170 earthquakes of type VT per day. Significantly, in the last 48 hours the magnitudes have again increased, with at least 10 earthquakes around magnitude 2.7. Because of the absence of data it has not been possible to locate these events with precision, however the arrival times of ’s’ and ‘p’ waves show that the earthquakes were concentrated on the south flank of the caldera.

3. CONCLUSIONS

The diminution in the height of the eruption column and the volume of emission has been correlated with a decrease in seismicity, which for four days has shown a large number of VT earthquakes of relatively greater magnitude. While the upturn in seismicity is not significant, the increase has been sustained over time, with an increase in the number of earthquakes surpassing, for the first time this month, the limit of magnitude 2.5.

The lower emission and height of the eruption column could be associated with an obstruction in the conduit, caused by the growth of the new dome. However, until now, there has been no evidence of a new pressurization of the upper part of the system. The presence of abundant pyroclastic and rocky material at the bottom of the caldera depression has been confirmed, which could cause blockage of drainage courses, the failure of which, in turn, could produce significant flooding of the Chaitén river during periods of heavy rain.

4. RECOMMENDATIONS

SERNAGEOMIN maintains Volcanic Red Alert and will continue with visual surveillance and processing, analysis and interpretation of related seismicity.

Photographs from the overflight of 30 June, and other recent images, can be found at the Gobierno Regional de Los Lagos website (warning: it’s a large, image-heavy page that can take some time to load).

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)