Etna update, 15 November 2011


Strong ash emission from multiple vents within the New Southeast Crater and on the southeast flank of its cone (at right) during the culminating phase of the paroxysmal eruptive episode of 15 November 2011, seen from  Torre del Filosofo, about 1 km to the south. Photo taken at 11:40 GMT (= local time -1) by Boris Behncke, INGV-Osservatorio Etneo (Catania)


Spattering from several vents along the eruptive fissure cutting the southeast flank of the New Southeast Crater cone, which first erupted during the paroxysmal episode on 29 August 2011. Photo taken at 09:50 GMT of 15 November 2011 from Belvedere, about 0.9 km southeast of the crater, by Boris Behncke, INGV-Osservatorio Etneo (Catania)


Eruption column produced by the paroxysmal eruptive episode of 15 November 2011, seen from the town of Bronte on the western flank of Etna. Photo taken by Giuseppe Anzalone and published here with kind permission of the author

18th paroxysmal eruptive episode from Etna's New Southeast Crater

After a quiescent interval of 23 days, the New Southeast Crater (New SEC) of Etna reactivated on the morning of 15 November 2011 to produce its 18th paroxysmal eruptive episode since the beginning of this year. This episode has in nearly all details been a repetition of its predecessors, though with a few minor variations; the culminating phase lasted about one hour and terminated rather abruptly. Ash and lapilli falls affected the southeastern flank, including the towns of Zafferana Etnea and Acireale.

The first signs of renewed eruptive activity at the New SEC were observed, by means of the thermal monitoring camera of the INGV-Osservatorio Etneo (Catania) at the Montagnola, about 3.5 km south of the summit craters, shortly after 06:00 GMT (= local time -1), when a small thermal anomaly appeared at the lower end of the eruptive fissure on the southeast flank of the cone. This anomaly slowly grew both in temperature and area, and was caused by the emission and expansion of a small lava flow that was being emitted from the lower end of the fissure. At about 08:00 GMT, mild Strombolian activity started within the New SEC, whereas spattering began from several vents along the fissure on the southeast flank of the cone. This activity continued for the next nearly 3 hours, while increasing very slowly, and the lava flow spread out into several branches at the southeastern base of the cone, advancing only a few hundred meters. At about 10:55 GMT, the activity showed a marked and rapid increase both within the crater and along the external eruptive fissure, and shortly after 11:00, lava fountains rose from the crater, accompanied by intensifying ash emission. Shortly thereafter, also the southeast flank fissure vents began producing lava fountains, and the cone was immediately subjected to heavy fallout of bombs and scoriae.

At about 11:30 GMT the emission of ash significantly increased, especially from a vent located in the southeastern portion of the  New SEC, and a column of ash and gas rose several kilometers above the summit of Etna before being bent southeastward by the wind. The phase of most intense activity occurred between 11:45 and 12:15 GMT, when jets heavily charged with incandescent bombs reached heights of about 800 m above the crater. This pyroclastic material poured down onto the New SEC cone and well beyond its base, and also showered the nearby old SEC cone. At a poorly defined time during this phase, explosions also occurred from a vent on the northern flank of the New SEC cone, probably the same vent that had emitted small lava flows on 28 September and 8 October. From thermal images recorded by the Monte Cagliato monitoring camera, on the ESE flank of Etna, there is no evidence for lava emission from this vent.

At about 12:25 GMT, the eruptive activity started to diminish, and then abruptly ceased at 12:29, to be followed by passive ash emission that lasted until shortly after 13:00. Weak and discontinuous spattering accompanied by slow lava effusion continued for a few hours from a single vent in the central portion of the eruptive fissure on the southeast flank of the New SEC cone.

The lava flow produced by this eruptive episode has followed the same path as those emitted during the previous episodes, toward the floor of the Valle del Bove, immediately to the north of the Serra Giannicola ridge, stagnating to the southwest of Monte Centenari. The flow reached a total length of little less than 4 km. The New SEC cone underwent further growth in height, mostly on its southern side, where at least 10 m of new material accumulated bringing the total height of the cone to about 180-200 m above its base.


At the climax of the paroxysmal eruptive episode of 15 November 2011, jets heavily charged with incandescent bombs rose up to 800 m high, as seen in this view taken from the flat area at the base of the Bocca Nuova, about 1.5 km SW of the New Southeast Crater. Photo taken at 12:15 GMT by Marco Neri, INGV-Osservatorio Etneo (Catania)

The 15 November paroxysmal episode occurred 23 days after its predecessor (23 October), the longest quiescent interval between paroxysms since early July 2011. In nearly all other respects, this event was a precise repetition of the preceding episodes, of similar duration, intensity, and quantity of eruptive products. Finally it is notable that the eruptive activity started just one hour after a magnitude 4 earthquake offshore the northern (Tyrrhenian) coast of Sicily, in the area between Capo d'Orlando and Sant'Agata di Militello.


The cone of the New Southeast Crater, seen from Belvedere at the beginning of the eruptive episode of 15 November 2011 (top) and after its cessation (bottom). The growth in height of the cone during the paroxysm is evident, in particular on its southern side (in the central part of both images), if compared to the peak of the old Southeast Crater cone at left. Photos taken by Boris Behncke, INGV-Osservatorio Etneo (Catania)

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