Puyehue-Cordón Caulle update, 13 June 2011 13 June 2011Posted by admin in activity reports, Chile, eruptions, Puyehue.
Above: Puyehue-Cordón Caulle, 13 June 2011: image from camera number 2 at 20:50 GMT. Below: by 22:05 GMT the sky is darkening over the volcano and incandescence is visible at the bottom of the plume (OVDAS-SERNAGEOMIN).
As the pictures at the head of this post indicate, the eruption at Puyehue-Cordón Caulle is still going strong. SERNAGEOMIN reported a largely stable situation in its bulletin no. 36 of 11 June 2011 (PDF), with seismic behaviour ‘little changed’ from that described in previous reports, and a repetition of the warnings of pyroclastic flows and lahars. Bulletin no. 37 of 12 June 2011 (PDF) reported that a helicopter overflight of the volcano had taken place during the previous day, and the following observations were made:
1. It was possible to verify that the emission centre is located at the head of the course of the Nilahue river, immediately to the north of the fissure along which the eruption of 1960 took place, where abundant accumulation of volcanic ash was observed, particularly in the headwaters of the Contrafuerte river.
2. There was also a significant accumulation of ash towards the eastern sector of Cordón Caulle, particularly on the west flank of Puyehue volcano.
3. Significant quantities of floating pumice were observed on the surfaces of Maihue, Huishue, Gris and Puyehue lakes.
4. The south-western part of Cordón Caulle and the western slopes of the Cordillera Nevada do not appear to be affected by ashfall.
The bulletin also notes that seismicity remains ‘largely unchanged’ from the previous report, although there was an explosion at 15:35 local time on 11 June that pushed the eruption column, usually around 4.0-4.5 km in height, up to 8 km altitude for a short time. Some of the areas to which access was previously restricted (Rucatayo, El Boquial, Lican and Mantilhue) have been opened up again, but SERNAGEOMIN continues to warn of the danger of lahars in areas affected by ashfall.
The most recent bulletin, no. 38 of 13 June 2011 (PDF) again reports seismicity ‘largely unchanged’ but notes a pulsing or cyclical behaviour in the tremor signal at the volcano:
… the seismic signal has been characterized by episodes of increase and decrease in the level of tremor, associated with an increase in the height of the eruption column, without significant registering of other types of earthquakes. There have been at least five cycles up to the time of publication of this report. The eruption column associated with the previous pulses of tremor reached heights of up to 8 km, with a very dense aspect, of dark grey colour, connected with ashfalls in surrounding areas due to partial collapses of the column.
Bulletin no. 38 also reports that there was another helicopter overflight by SERNAGEOMIN this morning, during which the following observations were made:
- During the flight the eruption column showed significant variations in height.
- It was confirmed that the eruption has been forming a cone at the emission centre, the crater has a diameter of approximately 300-400 metres.
- The presence of fragments with a ballistic trajectory up to slightly more than 1 km from the emission centre was verified.
- There is no great amount of ash to the west of the emission centre, while there was a great accumulation of pyroclasts to the east and north-east of that centre, in the headwaters of the Nilahue and Contrafuerte rivers.
- During the occurrence of emissions of increased intensity, the lower part of the column collapsed.
- The release of water vapour and gases at two or three points located north-west of the same fracture where the emission centre is located was observed.
The dangers of lahars and of the potential for the volcano to change its eruptive behaviour without warning are emphasized, and the alert level for Puyehue-Cordón Caulle remains at Red 6: ‘moderate eruption’.
Global Volcanism Program: Puyehue-Cordón Caulle volcanic complex – summary information for the PCCVC (1507-15=)
OVDAS-SERNAGEOMIN bulletins for Puyehue-Cordón Caulle – PDF files are available from this page of the OVDAS website