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Chaitén bulletins: no. 109 (30 October 2009) and no. 110 (13 November 2009) 24 November 2009

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In a remarkable development, SERNAGEOMIN has just released not one but two Chaitén bulletins to the public. Now available on the OVDAS ‘informes’ page are Chaitén bulletins 109 (PDF here, covering 16-30 October) and 110 (PDF here, covering 31 October to 13 November). Translations as follows.

CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 109
16-30 OCTOBER 2009
OVDAS-SERNAGEOMIN

1. Visual monitoring

During this period the volcano has remained obscured and only occasionally on 25 and 30 October has it been possible to observe the dome complex and its column of gas and ash. In general, the base of the column has appeared much wider, although the altitude has not exceeded 1.5 km above the domes (Fig. 1).

Chaiten 30 October 2009
Fig. 1. View from the DGAC camera in Chaitén on 30 October.

2. Seismic activity

Chaitén’s seismic activity has remained similar to that of the preceding period, with a prevalence of hybrid type (HB) earthquakes reaching an average of 15 earthquakes per hour and with magnitudes locally calculated to be within the range 1.5 to 4.2. Among these 2-4 earthquakes stand out each hour with magnitudes of above 3.5. Comparing the seismicity of this period with that of previous weeks, the seismic energy liberated RSAM has not exceeded 150,000 units.

3. Conclusions and interpretation

Both visually and seismically no large changes have been shown, and activity is consistent with that which has developed during the preceding period; this indicates that the eruptive activity continues with the growth of the dome complex.

On the other hand, the quantity of pyroclastic material both from rock falls and emitted by the block-and-ash flows and lateral explosions has created large accumulations in the adjacent valleys and particularly the valley of the Chaitén river, so that the occurrence of lahars towards Chaitén during periods of intense rain cannot be ruled out.

In consequence, given that the seismicity remains at elevated levels – an effect of the growth of the dome complex – and that the eruptive activity continues with the possibility of the generation of block-and-ash flows in random directions, which may affect surrounding valleys with the generation of new lahars, SERNAGEOMIN suggests maintaining Volcanic Red Alert.

OVDAS-SERNAGEOMIN
9 November 2009

[End of SERNAGEOMIN bulletin 109.]

CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 110
31 OCTOBER TO 13 NOVEMBER 2009
OVDAS-SERNAGEOMIN

1. Visual monitoring

The images observed through the DGAC camera located in Chaitén to the south of the volcano show that during 31 October and 1 November the eruption has continued to produce one column, principally consisting of water vapour with occasional gas and ash. Because of the predominant winds in the area the height of the column has not exceeded 1000 metres above the dome complex. During the rest of the reporting period the continuing [cloud] cover has prevented any visual observation of the activity (Fig. 1).

Chaiten 31 October 2009 (left), 1 November 2009 (right)
Fig. 1. Images from the DGAC camera in Chaitén on 31 October (left) and 1 November (right).

2. Seismic activity

In October SERNAGEOMIN personnel installed a triaxial seismological broadband station (CALDERA) at a distance of approximately 1.5 km from the centre of the Chaitén volcano dome complex. This station is on a trial run and will send real-time data to OVDAS for analysis, which will be incorporated into these bulletins.

With regard to the records of the STAB and PLL stations, the seismic activity has not shown major changes, with a continuing prevalence of hybrid type (HB) earthquakes reaching an average of 20 per hour and with magnitudes fluctuating between 1.5 and 4.1. Of these 2-6 per hour stand out with magnitudes exceeding 3.5.

The greater part of the seismicity presents very similar wave forms, which suggests an origin in the same source and through the same mechanism of origin.

3. Conclusions and interpretation

The seismicity has remained relatively stable compared with previous weeks indicating that the eruptive activity continues with the growth of the dome complex, observable only rarely recently because of the poor weather conditions in the area.

In consequence, given that seismic activity remains elevated as an effect of the growth of the dome complex, with the possibility of the generation of block-and-ash flows in random directions which may affect the surrounding valleys including the generation of new lahars, SERNAGEOMIN maintains Volcanic Red Alert.

OVDAS-SERNAGEOMIN
13 November 2009

[End of SERNAGEOMIN bulletin 110.]

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