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Etna update, 10 April 2011

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Lava fountains, eruption column and lava flow (in left foreground) during the paroxysm of 10 April 2011, seen from Monte Fontane, about 8 km to the east of the active vent, the pit crater on the eastern flank of the Southeast Crater cone. Photo taken by Boris Behncke, INGV-CT

The third paroxysmal eruptive episode of the year 2011 from the pit crater on the east flank of the Southeast Crater cone occurred on 10 April, 51 days after the previous paroxysm on 18 February. The event was essentially a repetition of its predecessors, with a lava flow probably exceeding 3 km in length, generation of a tephra and gas column, and intense lava fountaining.

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Colonna di cenere e gas prodotta dal parossismo del 10 aprile 2011, vista dal versante nord-orientale dell'Etna, vicino al rifugio Citelli. Foto di Boris Behncke, INGV-CT

During the night between 9 and 10 April, the Strombolian activity within the pit crater gradually increased, as did the volcanic tremor amplitude recorded by the INGV-Catania seismic network. The lava flow produced by the overflow initiated on the evening of 9 April advanced very slowly, and at sunrise on 10 April had not yet reached the steep western slope of the Valle del Bove.

During the forenoon of 10 April, the eruptive phenomena rapidly intensified, and a further significant increase in the volcanic tremor amplitude was observed, which culminated around 09.30 GMT (local time -2), with vigorous lava fountaining and the rise of an ash and gas column, which was blown by the wind to the southeast, causing ash falls in a sector between Trecastagni, Fleri, Zafferana, Aci S. Antonio, Acitrezza, Acicastello and Acireale. In this same interval, the rate of lava emission increased dramatically, producing a new flow that covered its predecessor before spilling down into the Valle del Bove, following essentially the same path as the lava flows of 12-13 January and 18 February. On its path, the lava flow locally encountered thick snow cover, which lead to violent explosive interaction that generated small pyroclastic flows and spectacular columns of vapor and ash.

Intense eruptive activity and ash emission continued until sometime before 14:00 GMT, and were followed by a rapid decline; no eruptive activity has occurred since the late afternoon.

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At the acme of the 10 April 2011 paroxysm, a vigorously fed lava flow rapidly advanced across terrain deeply covered in snow. Mixing of lava and snow led to powerful phreatomagmatic explosions, which, in turn, generated pyroclastic flows. In this view, the Southeast Crater is at right, and a black column of ash is rising from the active pit crater; the dark crest in the left background is the south wall of the Valle del Bove. The image was taken from Rocca della Valle, on the northern rim of the Valle del Bove, photographer Francesco Ciancitto, INGV-CT

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