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Etna update, 31 July 2011

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A mosaic composed of five photographs, taken from the "Belvedere" about 900 m southeast of the active crater on the east flank of the Southeast Crater cone, with lava fountains and the proximal portion of a lava flow descending toward the Valle del Bove, during the paroxysm on the evening of 30 July 2011. Photo taken by Boris Behncke, INGV-Catania

Eighth paroxysmal eruptive episode from Etna's Southeast Crater

On the evening of 30 July 2011, the eighth paroxysmal eruptive episode of this year took place from the crater located on the east flank of the Southeast Crater cone. The event was essentially a repetition of the previous paroxysms, with the emission of a lava flow toward the Valle del Bove, lava fountains rising to maximum heights of 450-500 m, and an ash plume that was blown by the wind toward east.

The first signs of a resumption of eruptive activity from the crater were observed on the evening of 28 July, when sporadic, and very weak, Strombolian explosions took place; this activity ceased altogether during the night. Throughout the whole day of 29 July, the crater remained entirely quiescent.

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Strombolian activity at the active crater on the eastern flank of the Southeast Crater cone on the morning of 30 July 2011, seen from Pizzi Deneri (about 3 km north fo the active vent).Photo taken by Marco Neri, INGV-Catania

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The old cone of the Southeast Crater (at left) and the active crater located on its eastern flank (at right), during the buildup phase toward the paroxysm, at about 20.35 h local time on 30 July 2011. Photo taken from Pedara, on the southeast flank of the volcano. Taken by Boris Behncke, INGV-Catania

From the early morning hours of 30 July, an intermittent glow was visible at the crater, which progressively increased in intensity and frequency. At about 10.00 h (local time = GMT+2), the crater showed intense Strombolian activity accompanied by loud detonations, with lava bombs thrown several tens of meters up into the air and falling back into the crater or around its rims. Contemporaneously, a dilute plume of ash was emitted from the vent, which was blown eastward by the wind. Furthermore, a small lava overflow occurred on the eastern side of the crater, which travelled about 100 m and then rapidly chilled.

This eruptive activity, which was accompanied by a distinct increase in the mean amplitude of the volcanic tremor, remained relatively constant until the early afternoon, after which an abrupt decrease occurred, both in terms of geophysical and volcanic activity.

About 19.00 h local time, the mean amplitude of the volcanic tremor started to incrase again, and so did the Strombolian activity. At around 19.30, a dilute gas and ash plume was again blown eastward by the wind. The Strombolian activity progressively gained in intensity, quite more rapidly than during the morning's activity, and the incandescent jets became continuous around 21.30 local time. At the same time, renewed lava overflow toward east showed a rapid increase in effusion rate, forming a multilobate flow down the western slope of the Valle del Bove, which travelled approximately 3 km down reaching about 2000 m elevation by 23.00 local time. The ash plume became denser and was blown eastward by the wind, generating ash falls in the Ionian sector of the volcano.

During the phase of maximum intensity, fragments of fluid lava were violently thrown to heights of about 450-500 m above the crater rim, causing heavy fallout onto the external flanks of the pyroclastic cone to a distance of 200-300 m. Lava fountains were jetting from at least two vents located within the crater and on its upper east flank, roughly aligned west-northwest - east-southeast.

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Detail of the proximal and distal portions of the lava flow emitted during the 30 July 2011 paroxysm. The photograph at left shows a lateral view on the flow descending the steep slope of the Valle del Bove; the image at right is a view down the lava flow toward its front (at lower left), with the lights of population centers on the east flank of Etna in the background. Photos taken by Marco Neri (left) and Boris Behncke (right), INGV-Catania

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Lava fountaining activity, ash plume, and lava flow from the new, and actively growing, cone on the east flank of the old Southeast Crater cone (barely discernible at extreme left), 30 July 2011. Photo taken from about 1 km distance to the southeast by Marco Neri, INGV-Catania

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Comparison photographs of the Southeast Crater, quiescent during daylight (29 July 2011) and during lava fountaining activity at night (30 July 2011). Both images were taken from the same position at Torre del Filosofo, about 1 km south of the Southeast Crater. The top photograph shows the large pyroclastic cone that has grown around the active crater, located on the eastern flank of the old Southeast Crater cone, during the seven paroxysmal episodes between 12 January and 25 July; further growth occurred during the 30 July paroxysm. In the bottom image, two vents within the active crater are seen producing lava fountains. The taller of these has a height of about 400 m, but in the moments of maximum intensity, rose up to 500 m high. Photo taken by Boris Behncke, INGV-Catania

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