Update on the activity of Etna and Stromboli, 12 August 2011


Eruptive column and ash plume drifting southeastward, produced by the paroxysm of Etna on the forenoon of 12 August 2011. The height of the eruption column is about 3 km above the summit of the volcano (3330 m). Note the veil of falling ash in the center and right portions of the image. The view is from the "Playa" beach, south of Catania, and about 30 km south of Etna's summit. Photo taken by Elisabetta Ferrera, Università di Catania

Tenth paroxysmal eruptive episode from the Southeast Crater of Etna

After an interval of relative quiet of 6 and a half days, the New Southeast Crater of Etna produced its tenth paroxysmal eruptive episode of the year during the forenoon of 12 August 2011. This event was, in its main characteristics, a repetition of its predecessors, with the emission of a lava flow toward the Valle del Bove, lava fountains several hundred meters high, and an eruption column that rose about 3 km above the summit. The ash plume was then blown southeastward, causing ash and lapilli falls in an area including the town of Zafferana and the coastal strip between Giarre and Acireale.


Image captured from video recorded by the thermal monitoring camera of the INGV-Catania on the Montagnola, about 3 km south of the summit craters of Etna, during an early phase of lava fountaining from the New Southeast Crater, at 08.42 GMT on 12 August 2011


Detail of the main lava fountain, containing abundant meter-sized, incandescent lava fragments and dark ash, about 09.42 GMT if 12 August 2011, seen from a distance of about 1.2 km to the south. Photo taken by Boris Behncke, INGV-Catania

At daybreak on 11 August 2011, sporadic ash emissions were observed at the New Southeast Crater, producing small pluffs of grayish brown ash. The visible light and thermal surveillance cameras of the INGV-Catania did not show any hot material in these emissions until late afternoon, when, after a short hiatus, the emissions resumed producing thermal anomalies. After sunset, small Strombolian explosions were observed at intervals of a few tens of minutes; this activity continued without variations during the night.

At about 05.30 GMT on 12 August, the Strombolian activity began to intensity, accompanied by an increase in the volcanic tremor amplitude, and the shift of the location of the volcanic tremor source from its previous position below the central summit area toward the Southeast Crater, migrating from greater to shallower depth. After  07.30 GMT, the Strombolian explosions produced dark ash puffs, and at 07.50 GMT, lava started to overflow the eastern rim of the crater, through a deep breach left open by the lava overflows of the previous paroxysms.

During the following 30 minutes or so, the Strombolian activity rapidly intensified, passing, at about 08.30 GMT, into a pulsating fountain about 100 m tall. Fifteen minutes later, a dense column of ash rose above the lava fountain, while the entire cone surrounding the New Southeast Crater was subjected to heavy fallout of large bombs and blocks.

Sustained lava fountaining and formation of an eruption column were most intense during the interval between 08.45 and 10.00 GMT, when three vents were active within the crater, two in its central portion and one close to the breach in its eastern rim. Shortly after 10.00 GMT, the two vents in the center of the crater emitted only ash, while the more easterly vent continued to launch jets of incandescent lava until 10.25. This was followed by a long phase of ash emission, which was often passive but at times more forceful; this activity completely ceased around 11.00 GMT.

The lava produced by this paroxysm descended on the western slope of the Valle del Bove, dividing into numerous lobes; the most advanced lava fronts reached the base of the steep slope above Monte Centenari. Ash and lapilli falls affected a relatively narrow sector between Zafferana and the coastal area between Giarre and Acireale, on the southeast flank of Etna.

Once more, the pyroclastic cone surrounding the New Southeast Crater underwent rapid growth, especially on its southeastern rim. The interval between this paroxysm and its predecessor was 6.5 days, slightly longer than the previous interval; it is notable, however, that since 19 July the intervals between the eruptive episodes have been very regular, varying between 5.5 and 6.5 days.


Lava fountaining from three vents within the New Southeast Crater during the forenoon of 12 August 2011, seen from Torre del Filosofo, 1 km south of the crater. The old Southeast Crater cone is seen at the center, and the Bocca Nuova is at left. Photo taken by Stefano Branca, INGV-Catania


The "double cone" of the Southeast Crater, the old one at left, and the new, growing one at right, photographed from the same site (near Belvedere, 1 km to the southeast) on 29 July (top) and 12 August 2011 (bottom). The interval between these images is thus two weeks, during which three paroxysms took place, on 30 July and on 5 and 12 August. Photos taken by Boris Behncke, INGV-Catania


Video frame captured by the thermal camera of the INGV-Catania on the Pizzo sopra la Fossa, at 00.00 GMT on 12 August 2011. At left, intense spattering is seen at the small cone on the rim of the crater terrace, which is entirely covered by fluid spatter generating rheomorphic flow down its flanks

Stromboli: spattering and small rheomorphic lava flow

Little more than two days after the previous episode of intense spattering at Stromboli, a new episode started on the evening of 11 August 2011 at the small cone that sits on the southwestern rim of the crater terrace. This episode lasted for a few hours and terminated early on 12 August. Spattering started at 18.15 GMT on the 11th, producing a small lava flow due to the accumulation of abundant fluid spatter on the steep flanks of the cone, which descended its eastern flank toward the flat bottom of the crater terrace. During the following hours, the whole cone was covered with rheomorphic lava, also on its external side. Normal Strombolian activity continued during this episode from the other vents on the crater terrace.
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