Ash and steam plume emitted during the paroxysmal phase of the eruptive episode of 8 October 2011 at the New Southeast Crater, seen from Trecastagni (about 15 km southeast of the summit of Etna), at 14:50 GMT (= local time -2). Photo taken by Boris Behncke, INGV-Osservatorio Etneo (Catania)
After little less than 10 days of relative calm, the 16th paroxysmal eruptive episode of this year at the New Southeast Crater (New SEC) of Etna has taken place on the afternoon of 8 October 2011. The culmination of this event, whose observation was very difficult due to bad weather, was rather brief but violently explosive, generating an ash cloud that was blown east-northeast by the wind. Once more, eruptive vents opened both on the southeastern and northern flanks of the New SEC cone.
|Strombolian activity and emission of lava flows from the eruptive fissure on the southeastern flank of the New Southeast Crater cone, seen from Belvedere, about 900 m southeast of the crater, at 14:14 GMT. Photo taken by Elisabetta Ferrera, University of Catania
The New Southeast Crater after the end of the 8 October 2011 paroxysm, seen from the western rim of the Valle del Bove about 2 km to the south, at 15:35 GMT. Lava is continuing to issue from the fissure on the southeast flank of the cone (at right), whereas a dilute ash plume is being emitted from the crater itself. Photo taken by Daniele Andronico, INGV-Osservatorio Etneo (Catania)
|The first clear signs of a reactivation of the New SEC were recorded by the instrumental monitoring network of the INGV-Osservatorio Etneo (Catania) on the morning of 8 October, when there was a rapid augmentation in the volcanic tremor amplitude. This was accompanied by a shift of the tremor source toward the surface, and from its “normal” location beneath the Northeast Crater toward the New SEC. At about 11:00 GMT (= local time -2) the start of eruptive activity was distinctly evident in images recorded by the surveillance cameras as weak and discontinuous Strombolian explosions. Two hours later (13:30 GMT), lava started to overflow from the crater, as usual through the deep notch in its southeastern rim.
At around 13:45 GMT, vigorous Strombolian activity was observed from numerous vents along a short eruptive fissure on the southeast flank of the cone, which had first been active during the 29 August paroxysm. After 14:15 GMT, weather conditions deteriorated, and the passage from Strombolian activity to sustained lava fountaining and ash emission was not directly observed. However, this passage, around 14:30 GMT, was well audible, and a dense ash and vapor plume rapidly rose above the weather clouds, and then drifted east. At the same time, a lava flow descended the western slope of the Valle del Bove, following the same path as the previous lava flows.
It was probably during this phase that eruptive vents opened on the northeastern flank of the cone, approximately along the fracture that had first opened during the 8 September paroxysm, and two small lava flows were emitted. The more voluminous of these, which issued from the lower end of the fracture, extended downslope for a few hundred meters to invade the central portion of the May 2008 eruptive fissure.
A panoramic view of the Valle del Bove and the New Southeast Crater during the 8 October 2011 paroxysm, seen from the Schiena dell’Asino on the southeast flank of Etna. Photo taken by Antonio Zimbone and published with kind permission of the author
The paroxysmal phase lasted little longer than 20 minutes and ended around 14:50 GMT; ash emission continued until about 17:45, when the volcanic tremor amplitude returned to levels similar to those preceding the paroxysmal episode, and the lava flow fronts appeared to stagnate. The ash cloud was blown east-northeastward by the wind, leading to ash and lapilli falls in a narrow sector that passed from the Ripe della Naca area and the village of Puntalazzo to the town of Mascali.
This paroxysm came little less than 10 days after the previous episode, and it was of shorter duration than any of its predecessors in the series initiated in January 2011 – the culminating phase of sustained lava fountaining and ash emission lasted only about 20 minutes. Another notable feature of this event is the minor eruptive activity on the northeastern flank of the New SEC cone, which occurred along the fracture of 8 September, oriented SSW-NNE in its upslope portion and bending SW-NE in its lower portion. In contrast, the fracture that opened in this area during the 28 September paroxysm lies further to the west, cutting the flank of the “Levantino”, a secondary cone formed in 2000-2001 on the north flank of the old SEC cone. The morphology of the New SEC did not undergo significant changes during this latest paroxysm, though it is likely that the accumulation of new pyroclastic material has led to some further growth in height of the cone.