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Etna update, 29 August 2011

20110829_fissure_730

A row of lava fountains plays from a new eruptive fissure that opened on the southeastern flank of the New Southeast Crater cone at  04.21 GMT (local time -2), one minute after the opening of the fissure. A dull red lava fountain in the center rises from the vent located in the center of the crater; the old Southeast Crater cone is at left. The lava flow seen at right was emitted until the opening of the new eruptive fissure. Photo by Boris Behncke, INGV-Catania

12th paroxysmal eruptive episode from Etna's Southeast Crater

Nine days after the previous episode, the New Southeast Crater produced its 12th paroxysmal eruptive episode of the year on the early morning of 29 August 2011. This episode was particular for the opening of a new eruptive fracture on the southeastern flank of the pyroclastic cone surrounding the crater, along which several lava fountains shot up, and from which a broad lava flow was emitted that took a more southerly path compared to that of the earlier lava flows. The pyroclastic cone underwent major morphological changes due to the opening of the new eruptive fracture, which left a deep cleft in its southeastern flank. However, further growth occurred on the southern and northern rims of the crater. This episode produced a tall eruption column, which bent southeast, leading to ash and lapilli falls in population centers such as Zafferana Etnea, Fleri, Viagrande, and Trecastagni.

The episode was preceded, as its predecessors, by initially very discontinuous and weak activity, which started with a single explosion at 00.52 GMT (= local time -2) on 28 August, followed from 15.17 GMT on by a series of ash emissions from the New Southeast Crater. At nightfall, sporadic, weak Strombolian activity was visible, which during the night showed a gradual intensification. At 03.15 GMT on 29 August, a first lava overflow occurred through the deep breach in the eastern crater rim, feeding a flow into the direction of the Valle del Bove. From 03.40 GMT onward, the Strombolian activity progressively intensified, and about 04.05, two vents within the crater emitted pulsating lava fountains up to 100 m high. During the following 10 minutes, these fountains increased significantly in height, and a dense eruption column rose a few kilometers above the summit of Etna before drifting toward south-southeast. At the same time, a small lava flow began to issue from the area affected by the collapse of a portion of the cone's east-southeast flank during the 20 August paroxysm.

At 04.20 GMT, the southeastern flank of the cone fractured with the opening of a line of new eruptive vents down to the base of the cone, from which a row of lava fountains rose (see the image at top); soon thereafter a new, broad lava flow appeared, which was fed from the new vents, and which descended into the direction of the Valle del Bove, somewhat to the south of the lava flow emitted earlier during this episode. For the next 20 minutes, lava fountaining continued at all vents, both within the crater and along the new fracture, then the activity started to weaken from 04.30 GMT on. The lava fountaining from the vents within the crater passed into ash emission shortly after 04.40, whereas the lowest vent on the new eruptive fracture continued to produce incandescent jets until 04.50 GMT. Ash emission continued at a diminishing rate until about 05.15 GMT.

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