jump to navigation

Chaitén bulletin no. 79 (25 February 2009) 1 March 2009

Posted by admin in activity reports, Chaitén, Chile, eruptions.
Tags: , , , ,
trackback

SERNAGEOMIN bulletin no. 79 on the eruption of Chaitén volcano was issued on 25 February 2009 and essentially reports the findings of the overflight carried out on that day. The original text can be found at the OVDAS website (PDF) and a slightly edited version is also available on the SERNAGEOMIN site. Translation as follows.

ERUPTION OF CHAITÉN VOLCANO
TECHNICAL BULLETIN NO. 79
25 FEBRUARY 2009
OVDAS-SERNAGEOMIN

Visual monitoring

On an overflight carried out today, 25 February, in a Chilean Air Force helicopter, with specialists contracted by ONEMI to perform thermal measurements, it was confirmed that the eruptive activity described in the previous bulletin has been maintained, that the remnant of dome 1 in the southern sector is found to be active and growing, as is the pinnacle, which presents very steep and unstable slopes (Fig. 1). On the other hand, volcanic material, the product of partial collapses of the pinnacle and dome 1, continues to accumulate upon the extensive fan of blocks and ash located at the foot of the collapse escarpment.

In addition, it was observed that dome 1, in the south-eastern quadrant, is very unstable (Fig. 2), making it highly likely to collapse, generating pyroclastic flows towards the east and towards the drainage channel of the basal ring of the dome complex.

New estimates today confirm the dimensions of the escarpment of the major collapse last Thursday. The north-eastern axis is 500m, the north-western axis is 300m with an average depth of 300m, in a wedge shape.

Thermal measurements

The preliminary data (A. Pávez, oral communication) indicate temperatures in the order of 270ºC at the pinnacle, 200ºC at the south remnant of dome 1 and lower temperatures at dome 2, in the north sector. This suggests that the current magmatic activity is concentrated in the southern sector of dome 1 and at the pinnacle. In addition, the water of the río Chaitén in the portion affected by the pyroclastic flows and rocks and ashes is about 50ºC in the middle to lower portion of the channel, which rises to 70ºC in the middle part, where the flow deposits, associated with the partial collapse (19.02.09) reached temperatures of 130ºC. Additionally, there are thermal alignments with an approximately north-south orientation in the south slope of the currently active remnant of dome 1. It should be noted that this sector of the dome did not present a notable thermal anomaly during the measurements taken in the month of January of the present year, which occurred at the pinnacle. The final detailed figures and interpretations of this study will be contained in the respective report which will be issued by the expert and promptly delivered to ONEMI and SERNAGEOMIN.

Figure 1.
Figure 1. Geometry and dimensions of collapse, of pinnacle and of domes 1 and 2 (photograph P. Duhart). [N.B. In this image, English translations of terms are pasted directly over the Spanish originals. The term ‘H2O(g)>Pyroclasts’ indicates that in this area of emissions, water vapour predominates over pyroclastic material; the reversal of the ‘>’ indicates that the relative proportions are reversed.]

Figure 2.
Figure 2. South-eastern slope of the south remnant of dome 1, which displays instability, abundant emissions of steam, gases and ash, with in addition numerous partial collapses generating block and ash flows on its slopes (photograph P. Duhart).

Seismic activity

The seismicity recorded by the Chaitén volcano seismic network presents no major changes in comparison to that reported in the previous bulletin no. 78, with 1-2 HB-type earthquakes with magnitudes less than 3.6, located beneath the volcano. The University of Chile Seismological Service reports today a very shallow earthquake with a magnitude of 2.7 at 10:30.

Conclusions

The eruptive activity remains unchanged and confirms the activity and growth of the pinnacle and the south remnant of dome 1. In addition there is instability of significant sectors of the dome complex (for example, south-eastern slope), the pinnacle and the steep sides of the limits of the collapse. The seismic activity recorded maintains the characteristics that have been present during the last few weeks.

Taking into account the characteristics of the seismicity recorded in the area of the volcano, the continuing probability of the occurrence of new large collapses of significant portions of dome 1 and of the pinnacle, generating explosions and associated pyroclastic and ash flows , along with the probability of further lahars during periods of prolonged and intense rainfall, SERNAGEOMIN maintains Volcanic Red Alert.

[End of SERNAGEOMIN 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

The Volcanism Blog