The 12 April 2012 paroxysm of Etna

Figura 1. Eruption column rising from the New Southeast Crater of Etna during the paroxysmal eruptive episode on 12 April 2012, seen from the port of Catania, about 25 km south of the summit of the volcano. The white vapor column in the lower center is the result of explosive interaction between lava descending toward the Valle del Bove, and thick snow covering the ground, a phenomenon that has been repeatedly observed during recent paroxysmal eruptive episodes at Etna. Photo taken by Simona Scollo, INGV-Osservatorio Etneo (Catania)

On the afternoon of 12 April 2012, the New Southeast Crater (New SEC) of Etna was the site of the 24th episode of lava fountaining (paroxysm) in the current eruptive sequence initiated in January 2011, and the 6th in this year (Figure 1). As its predecessors, this episode was characterized by high lava fountains from several vents, a tephra column several kilometers tall, leading to ash and lapilli fallout in the eastern sector of the volcano, and lava flows descended toward theValle del Bove, locally showing violent explosive interaction with the snow covering the terrain.

The "prelude" to this episode began with a series of explosions from the New SEC on the evening of 10 April, followed by intermittent Strombolian activity that was occasionally accompanied by small ash puffs in the next 24 hours. On the evening of 11 April, the Strombolian activity was well visible and continuous, but without showing any significant variations. On the morning of 12 April, field observations made by INGV-Osservatorio Etneo staff, revealed that vigorous Strombolian activity was continuing from a vent lying in the eastern portion of the crater; this activity gradually increased in intensity over the next few hours.

Figura 2. Strombolian activity and beginning of lava emission, during the "prelude" to the paroxysmal eruptive episode of 12 April 2012, during the interval between 13:00 and 30:30 GMT. Note, in the lower image, the spattering from a vent located in the breach that cuts the southeastern rim of the New Southeast Crater. Photos taken by Emanuela De Beni (top) and Daniele Andronico (bottom), INGV-Osservatorio Etneo (Catania)

Between 12:00 and 13:00 GMT, the crater progressively filled with lava; around 12:24 GMT, a small lava flow began to make its way down the southeast flank of the New SEC cone (Figure 2, top). The source of this lava flow was apparently a vent located on the upper southeast flank of the cone, within the deep breach that cuts the southeastern rim of the crater. Starting around 13:20 GMT, this vent showed vigorous spattering activity (Figure 2, bottom). Between 13:40 and 13:45 GMT, an explosive vent became active within the western portion of the crater, giving Strombolian explosions along with discontinuous emission of dilute ash. Between 14:20 and 14:30 GMT, the Strombolian activity rapidly passed into sustained lava fountaining, first from the westernmost vent, and then also from the one in the eastern part of the crater. Shortly after 14:30 GMT, also the vent that lay in the breach in the southeastern rim of the crater, started to produce continuous jets of lava, which were strongly inclined toward east. The beginning of lava fountaining was accompanied by the generation of an eruption column heavily charged with pyroclastic material, which rose about 3 km above the summit of the volcano before being bent eastward by strong wind. Ash and lapilli fell in a sector including the villages of Fornazzo, S. Alfio, Puntalazzo and Nunziata on the middle slopes of the volcano, and Mascali closer to the Ionian Sea.

In the meantime, the lava flow issuing through the breach in the southeastern rim of the crater, had begun descending the steep western slope of the Valle del Bove, following the same path as the preceding lava flows, and splitting into several branches, some of which invaded areas covered with thick snow. As during several earlier eruptive episodes, the interaction between lava and snow was locally violently explosive (Figures 1 and 3), generating ground-hugging clouds of vapor and ash as well as lahars (mudflows), and columns of vapor that rose up to 1 km high. During the phase of most intense lava fountaining, a vent located on the northern flank of the New Southeast Crater cone emitted a lava flow that reached the middle-lower portion of the May 2008 eruptive fissure on the upper eastern flank of Etna. The flow descended along the fissure for a few hundred meters before it was diverted by a small cone sitting on the fissure and continued another 150 m on the northern side of the fissure.

Figura 3. Lava fountain and dark gray eruption column from the New Southeast Crater (at left), and white vapor column generated by explosive interaction between lava and snow on the groun (at right) at the height of the 12 April 2012 eruptive episode. At the base of the white plume, one of the peculiar ground-hugging clouds of vapor and ash can be seen, a phenomenon that has become rather common during Etna's paroxysms in the winter season. The view is from southeast. Photo taken by Grazia Musumeci and published here with kind permission of the author (original version on Flickr)

Lava fountaining continued intensely until shortly before 15:00 GMT, when the westernmost vent began to show a marked diminution in its activity; subsequently also the other vents showed diminished activity, and around 15:15 GMT, lava fountaining from all vents had passed into ash emission which initially was rather strong but then gradually lost strength and ceased around 16:00 GMT.

The 12 April 2012 eruptive episode took place 10.5 days after the previous episode, a shorter interval than those between the latest episodes. The last interval of similar length was that between the paroxysms of 28 September and 8 October 2011. In all other details, this episode was a repetition of its predecessors, and it led to only modest growth of the pyroclastic cone of the New SEC.