SERNAGEOMIN reduces Chaitén alert level to Yellow 25 June 2010

Here are the two most recent Chaitén bulletins from SERNAGEOMIN to be made publicly available (at the OVDAS website and at the comprehensive Chaitén site run by Werner Luis): no. 119 covering 1-31 May 2010 (PDF) and no. 120 covering 1-15 June 2010 (PDF). The main news is that the alert level for the volcano has been reduced from the highest level of Red to Yellow, reflecting SERNAGEOMIN’s judgement that the eruption is in decline. Translations as follows.

REPORT NO. 119 ON THE LEVEL OF ACTIVITY OF CHAITÉN VOLCANO 1-31 MAY 2010

The alert level for the volcano is changed to LEVEL 4 – YELLOW: CHANGES IN THE BEHAVIOUR OF THE VOLCANIC ACTIVITY (eruption probable in days or weeks).

On the basis of analysis of information obtained from monitoring equipement and observation of Chaitén volcano, the Servicio Nacional de Geología y Minería (SERNAGEOMIN) – Observatorio Volcanológico de los Andes del Sur (OVDAS) reports for this period as follows:

• A total of 140 seismic events were recorded, of which 77 were related to rock fracturing. These were principally located around and to the south of the volcanic caldera, at depths of less than 7 km.
• Regarding fluid dynamics, 63 earthquakes were identified, mostly of low energy, possibly related to hydrothermal processes and/or the release of magmatic gases at low pressure.
• The images received from the cameras installed around the volcano highlighted four fundamental aspects: (1) no occurrence of ash emissions; (2) days with minimal degasification at the surface of the dome; (3) days with degasification of the dome complex much enriched with water vapour and at low pressure, this last related to periods of rain and atmospheric humidity; (4) at least two small zones of nocturanal incandescence, located on the north-west flank and centre of the dome complex.
• Through the images published by the OMI (the Ozone Monitoring Instrument Sulphur Dioxide Group) no changes were detected in the emission of SO2 to the atmosphere

Seismic activity has been characterized by low energy, such as has been recorded since January 2010, which confirms that there have been no new eruptive processes of magma movement, and little release and movement of volcanic gases within the conduits has been detected, which may be related to the cooling process of the dome complex.

From the foregoing, it is concluded that the current eruptive process is moving into a phase of decline, with few [eruptive] manifestations. Consequently, the volcanic alert level is changed to LEVEL 4 – YELLOW. It is stressed that it is possible for the system to move to new phases of disequilibrium and eruptive stages. Given the large size of the dome there is a continuing danger of collapses, possible explosions and the generation of block and ash flows which may affect the valleys surrounding Chaitén volcano. Also, there is a continuing danger associated with the transport and sedimentation of volcanic materials, including fine ash, along adjacent river valleys and their mouths in coastal areas, particularly during heavy and prolonged rain.

SERNAGEOMIN continues monitoring and will announce in a timely manner any changes in the volcano’s activity.

SERVICIO NACIONAL DE GEOLOGÍA Y MINERÍA – SERNAGEOMIN
Observatorio Volcanológico de los Andes del Sur – OVDAS
31 May 2010

[End of SERNAGEOMIN bulletin no. 119.]

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