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Etna update, 8 August 2011

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Lava flow on the western slope of the Valle del Bove at the end of the eruptive episode of 5-6 August 2011, seen from Monte Fontane, on the eastern slope of Etna. The New Southeast Crater is visible at upper right. Photo taken by Daniele Andronico, INGV-Catania

Ninth paroxysmal eruptive episode from Etna's Southeast Crater

Six days after its predecessor, a new paroxysmal eruptive episode has taken place at the New Southeast Crater (previously called "pit crater", located on the east flank of the old Southeast Crater cone) of Etna, during the night of 5-6 August 2011. In its main characteristics, this event has been a repetition of the previous paroxysms, with the emission of a lava flow toward the Valle del Bove, lava fountains exceeding 500 m in height, and an ash cloud blown southeast by the wind; however, this was one of the shortest and most violent paroxysms of the sequence initiated at the beginning of this year.

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Frames captured from video recorded by the INGV-Catania thermal monitoring camera at the Montagnola, about 3 km south of the summit craters of Etna, during the different phases of the paroxysm at the New Southeast Crater on the late evening of 5 August 2011

The first signs of an imminent new eruptive episode were observed on the afternoon of 5 August, when weak Strombolian explosions started within the crater. This activity gradually increased over the following hours. About 20.15 GMT (= local time -2), a lava flow started to spill over the low east rim of the crater, and then followed the same path of the lavas emitted during the previous paroxysms, toward the western slope of the Valle del Bove. The Strombolian activity within the crater began to show a rapid increase in intensity shortly before 21.00 GMT, and passed into near-continuous fountaining to about 100 m above the crater rim.

Between about 21.30 and 21.50, the activity further intensified, with jets of lava several hundred meters high, and an eruption column laden with ash and lapilli, which rose a few kilometers above the summit of the volcano, and then was blown southeastward by the wind. At the climax of the paroxysm, the lava fountains sometimes exceeded 500 m in height. Shortly after  22.15 GMT, the incandescent jets diminished notably in height, and continued in a pulsating manner for about an hour, showing a further diminution about 23.00 GMT, and at 00.15 on 6 August, the paroxysm was substantially over.

The lava descended, in various branches as during the previous paroxysmal episodes, on the western slope of the Valle del Bove, reaching the base of the steep slope near M. Centenari. The maximum length of the lava flow is thus inferior to that of the flow emitted during the preceding paroxysm, on 30 July 2011. Ash and lapilli falls were observed in the southeastern sector of the volcano, between Zafferana and Viagrande on the mountain, and between Acitrezza and Pozzillo along the Ionian coast. The main axis of the pyroclastic deposit passes between the villages of Fleri and Zafferana, and further downslope, at Acireale.

This ninth paroxysmal eruptive episode of the year at the New Southeast Crater has led to major growth of the pyroclastic cone that is building up around the crater, especially in its southeastern portion. The episode came 6 days after its predecessor, an interval that is very similar to those between the previous few episodes, but the "prelude" and buildup phase (Strombolian activity - lava flow emission) has been much shorter compared to the other events.

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The Southeast Crater seen from northeast after the paroxysm of 5-6 August 2011. At right stands the old cone with its sulfur deposits corresponding with the zone of persistent fumarolic activity on the upper east flank of the cone; the summit vent of this cone last erupted on 6-7 May 2007. At left is the New Southeast Crater surrounded by a conspicuous pyroclastic cone; the eastern crater rim is cut by a deep breacy (at left), where lava has overflowed during all paroxysmal eruptive episodes of this year, preventing accumulation of pyroclastics. Photo taken by Boris Behncke, INGV-Catania
 
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