Llaima update, 8 April 2009 9 April 2009Posted by admin in activity reports, Chile, eruptions, Llaima.
Tags: Chile, Llaima, South America, volcanic activity reports, volcanic eruptions
The Chilean state geological service SERNAGEOMIN seems to have had some kind of technological crisis over the past 24 hours, with their main site intermittently inaccessible, and the Observatorio Volcanológico de los Andes del Sur (OVDAS) site still broken as of posting time. The latter site is so ugly and annoying that its total disappearance would be little cause for regret, except that it is where SERNAGEOMIN post PDFs of their volcanic activity bulletins, when they get around to it. The following bulletin on Llaima (8 April 2009) and a second short report (8 April 2009, 10:30) therefore come from the main SERNAGEOMIN site, which is currently back in the land of the living.
08.04.2009 SERNAGEOMIN Bulletin on Llaima Volcano
After 74 hours of a vigorous strombolian eruptive phase, accompanied by emissions of lava, on 6 April at 23:00 the eruption declined abruptly in intensity until it reached a very weak level with little ash emission, this phase ending on 7 April at 14:00.
The main crater has been blocked by a large pyroclastic cone, which surpasses in height the edge of the highest peak of the volcano.
Currently, the volcano is maintaining only gaseous emissions in the form of a weak fumarole. The seismic signal corresponds to earthquakes of LP [long period] type (up to 20 per hour) with an average of 30 units RSAM.
During 5 April most of the volcano has been permanently obscured. In the morning a lahar was reportedly generated towards the río Captrén which cut the road between Curacautín and the Conguillío National Park. In the afternoon it was possible to see part of the plume of ash, of dark grey colour, directed towards the east.
Throughout the following day, 6 April, there remained poor visibility conditions, although occasionally it was possible to see the cloud of gas and ash directed principally towards the east (Lago Verde). During the afternoon it was possible to confirm the cutting of the road in the Captrén area and possibly to hear periodic explosions associated with the fall of ash and fine lapilli towards the north-east.
The column was of much lighter colour (little ash concentration) indicating a diminution in the intensity of the eruption. During the night no incandescence or glow was seen.
In the morning of 7 April, meanwhile, only weak emissions of ash and volcanic gases were observed. On this day an overflight was carried out by an aircraft of Club Aéreo de Temuco, in the company of the Governor of Cautín, Mr Christian Dulansky. The principal observations made were as follows:
The main crater of the volcano is completely covered and obstructed by a large pyroclastic cone with four inactive craters, with only gaseous emissions of sulphur dioxide and hydrochloric acid.
On the west flank two main lava flows were observed, the southern flow with a length of some 4.5 kilometres, which had been completely encased in the glacier and blocks of ice upon it, which melted and evaporated, carrying dark brown-coloured water into the río Calbuco. The northern flow had a similar length, and was held up and divided into two arms of 1 kilometre, one towards the headwaters of the río Calbuco and the other towards the headwaters of the río Lanlan, with a lesser load of water entering the area of the shelters.
On the north-east flank another lava flow came from the base of the pyroclastic cone towards the headwaters of the río Captrén (Fig. 3), which generated lahars which descended this valley and cut the road between Curacautín and the Conguillío National Park (Fig. 4).
The glacier on the west flank of the volcano showed cracks and ridges of ice, suggesting creeping of the glacial mass. During the overflight of 4 April the glacier and its cracks were completely covered by the mantle of pyroclasts.
The headwaters of the río Calbuco showed a large burden of muddy water moving through various tributaries, however, it was possible clearly to see the saturation of most of it [with volcanic deposits], since at the road bridge (between Cherquenco and Melipeuco) the water flow was much lower. Remains of tree trunks along its path were evidence of the passing of the lahars that were reported on 4 April.
The seismic activity which occurred on 5 and 6 April continued to register an energetic tremor, which seismic energy oscillated between 900 and 1600 units RSAM. Moreover, on 6 April at 20:33, a superficial VT-type [volcano tectonic] earthquake was recorded with a magnitude of 1.5, with an epicentre beneath Llaima volcano. Two and a half hours later, at 23:00 approximately, in a sudden way, the energetic tremor declined from 1100 to 19 RSAM units in just under two hours, a phenomenon common in this eruptive cyle which began in May 2007. Finally, during today, seismic activity has been characterized by up to 20 LP-type earthquakes per hour, of low amplitude, with an oscillation of RSAM values between 15 and 50 units.
As explained above, the status of Llaima volcano remains critical because of its erratic behaviour and the obstruction of its crater. If there is an eventual reactivation, the most critical areas are the valleys of the Calbuco, Lanlan and Captrén rivers, because of the possibility of the generation of lahars. Moreover, the generation of ashes, affecting principally the sector east of the volcano.
In consequence, SERNAGEOMIN maintains Red Alert while this post-eruptive situation continues.
[End of SERNAGEOMIN bulletin, 8 April 2009.]
08.04.2009 SERNAGEOMIN Bulletin on Llaima Volcano (10:30)
During the night it was possible from Melipeuco to see intermittent incandescence at the south-west foot of the large pyroclastic cone that completely fills the main crater. From this lava was emitted at a very low rate and incandescent blocks rolled down the slope of the volcano.
Today, 8 April, from dawn until the present hour a very weak fumarole of volcanic gases (SO2 and HCI) has been seen which emerges from various points on the summit of the pyroclastic cone and forms a thin fumarolic plume in a north-east direction because of the prevailing winds from the south-west.
Preliminary calculations have enabled the indication that the height of the large pyroclastic cone surpasses by 70 metres the summit of the principal crater, that is to say, Llaima volcano would have a current altitude of 3240 metres above sea level (originally 3169 meters above sea level).
In relation to the seismicity, this remains at very low levels characterized by the presence of LP-type earthquakes (up to 20 per hour), of little energy, with RSAM varying between 17 and 19 units during the last few hours.
SERNAGEOMIN continues with permanent visual and seismic monitoring from various points around the volcano, evaluating, in addition, the effects of the last eruptive phase, and maintaining Red Alert.
[End of SERNAGEOMIN bulletin, 8 April 2009, 10:30.]
For all our Llaima coverage: Llaima « The Volcanism Blog.
Global Volcanism Program: Llaima – summary information for Llaima (1507-11=)
Oficina Nacional de Emergencia – Chilean government emergencies office
SERNAGEOMIN – Servicio Nacional de Geología y Minería, Chile
Proyecto Observación Visual Volcán Llaima – Llaima Visual Observation Project