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Llaima: SERNAGEOMIN bulletin, 4 April 2009 5 April 2009

Posted by admin in activity reports, Chile, eruptions, Llaima.
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The Chilean state geological service SERNAGEOMIN have issued a bulletin on the current eruptive activity of Llaima volcano, dated 4 April 2009, which is available on their website. Translation as follows.

UPDATE 8 APRIL 2009: A more detailed bulletin dated 4 April 2009 has been released and is available via OVDAS as a PDF file. For a translation of this longer bulletin, scroll to the bottom of this post and click ‘more’.

04.04.2009 SERNAGEOMIN Report on the Reactivation of Llaima Volcano

Following several months of low seismic activity, Llaima volcano has begun a new eruptive phase that forms part of the cycle that started in mid-2007.

On 2 April at 16:00 (local time) a slight rise in seismicity was detected that was manifested in a growth in the amplitude and frequency of LP-type earthquakes (long period earthquakes), reaching 45 to 60 earthquakes per hour.

This increase remained constant until 18:00 on 3 April, then evolving into a continuous seismic tremor, of low frequency but greater magnitude. The slight increase in activity recorded on 2 and 3 April was associated with weak emissions of water vapour (and apparently low ash content).

From 20:30 on 3 April, eyewitnesses in the area reported glowing in the main crater, which stood out in the prevailing cloudiness. At 21:00 the tremor again slightly increased, while at 22:45 explosions of a weak strombolian type were reported in the north cone situated within the main crater. This weak, but permanent, strombolian activity was associated with a tremor recorded from 18:00 yesterday, a situation that remained constant until 23:45, when a further increase in seismicity was observed.

Until 06:00 today, 4 April, the strombolian-type activity remained moderate in intensity, with rhythmic explosions every 1-3 seconds from the two pyroclastic cones nested within the main crater. The projection of incandescent pyroclastic material reached up to 700m above the crater. Since the beginning of this eruptive phase lava flows have descended the western flank, maintaining the same course as the flows emitted in previous eruptions in this cycle.

At 02:50 today, 4 April, the condition of the Calbuco river channel was checked at the bridge between Cherquenco and El Salto. Flow was assessed as normal, and the water had a muddy colour.

The seismic energy released (RSAM) remained relatively stable at 25 units until 16:00 on 2 April. At 20:00 on that day it was slightly elevated to 40 units and rose sharply to 70 units at 14:00 the following day, with an average of 60 units maintained until 20:00 on 3 April. Subsequently, the energy liberated increased rapidly to reach 800 units at 23:00 on 3 April, 1400 units at 03:30 on 4 April, and then descended to 1100 units at 06:30 on the same day, with a decline in the intensity of the eruptive activity.

Given that since the beginning of the present eruptive cycle Llaima volcano has shown sudden changes in behaviour and in its seismicity, currently presenting a revival of strombolian-type [activity], with variable seismic energy released, SERNAGEOMIN again establishes RED ALERT for Llaima volcano and will continue to evaluate the evolution of this new eruptive phase.

[End of SERNAGEOMIN bulletin.]

The following is a translation of a longer SERNAGEOMIN bulletin dated 4 April 2009 (available via OVDAS as a PDF file).

20 MARCH TO 4 APRIL 2009

1. Visual monitoring

From 20 March to 3 April, weak emanations of water vapour and slight ash emissions were occasionally observed, from the cones nested within the principal crater of the volcano.

At 21:00 on 3 April Mr Miguel Yarur reported the beginning of an eruption with notable red glares at the summit of the volcano. From Melipeuco and at 01:30 it was possible to confirm the development of a strombolian eruption with projection of incandescent pyroclasts up to 700 metres above the crater and a plume with a little fine ash directed towards the east. In addition, a lava flow commenced on the western flank, where significant steam emissions could be seen at the same time. The rhythmic explosions every 1-3 seconds maintained their intensity until 07:00 on 4 April 2009. From 08:00 the progress of the eruption was gradually intensified and at 12:00 powerful explosions were heard in Melipeuco. At 06:30 and 08:30 small lahars were produced which cut the road in the El Danubio area (río Calbuco). In a helicopter overflight between 12:45 and 13:30 it was possible to confirm the growth in intensity of the eruption, the presence of three lava flows descending towards the west, a dense black column of gas and ash that formed a dark grey plume of up to 7000 metres altitude and extending more than 100 kilometres to the south east (Icalma and Aluminé), the deposition of incandescent material up to 2km towards the north-east (Captrén), and the generation of a pyroclastic flow on the western flank (Figs. 1, 2, 3 and 4). From the fronts of two lava flows large volumes of water saturated with ashes were discharged towards the headwaters of the río Calbuco. The eruption began to decline in intensity towards 18:00. Nevertheless, from 18:20 it again intensified with a notable increase in the rate of emission of lava and of the column of gas and ash. Towards 20:00 today [4 April 2009] the eruption, which has lasted more than 23 hours, has maintained its intensity, with further powerful explosions audible in Melipeuco.

2. Seismic activity

From 20 March up to 2 April seismicity has remained low with a weak tremor of around 15 to 25 RSAM units. From 3 April, the energy released by the tremor increased gradually, rising suddenly at 20:00 to reach 800 RSAM units at 23:00 and 1400 units at 03:30 on 4 April 2009, stabilizing at 1300 units during the morning of 4 April 2009. Between 14:00 and 20:00 the RSAM value has remained at some 1100 units (Fig. 5).

3. Conclusions and interpretation

In conjunction with the sudden increase in the seismic energy liberated at 21:00 on 3 April 2009 began a new development of another eruptive phase of strombolian type which continued for more than 23 hours, part of the eruptive cycle initiated on 27 May 2007.

Currently, the volcano remains stable in its strombolian phase with dense and continuous emissions of gas and ash, accompanied by lava emissions which drain towards the western and north-eastern flanks. The seismic signal corresponds fundamentally to a very energetic tremor with an average of 1100 RSAM units.

The most critical areas in this new eruptive phase are the valley of the río Calbuco, possibly the valley of the río Lanlan (if the lava flow moves in a more northerly direction) and the headwaters of the río Captrén, due to the possible generation of lahars. However, the permanent plume of ash has caused significant falls of particulate material principally towards the south-east (Icalma, Aluminé).

In consequence, SERNAGEOMIN maintains Alert Level Red while the strombolian eruption continues.

Figs 1 to 4. Overflight carried out on 4 April 2009 at 14:00:

Figure 1
Figure 1 shows the pyroclastic projections, the dense emission of gas and ash and the lava flows down the western flank.

Figure 1
Figure 2, the flows descending towards the valley of the río Calbuco and the north (arrow), perhaps reaching the río Lanlan.

Figure 1
Figure 3, the flow of incandescent material towards the valley of the río Captrén.

Figure 1
Figure 4, the generation of a pyroclastic flow down the eastern flank.

Figure 1
Figure 5. Graph of the seismic energy released by tremor at Llaima volcano between 1 and 4 April 2009.

[End of SERNAGEOMIN bulletin.]

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

The Volcanism Blog