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The 16 March 2013 paroxysm of Etna

Fig. 1. The great lava fountain from the New Southeast Crater (NSEC) during the episode of lava fountaining on the evening of 16 March 2013, seen from Randazzo (15 km distant from the crater, on the north-northeastern flank of Etna). The conspicuous cone whose silhouette is visible at the base of the lava fountain is the Northeast Crater. Photo taken by Gaetano Scarpignato and published here with kind permission by the author.

On the evening of 16 March 2013, the New Southeast Crater (NSEC) of Etna produced the eighth episode of lava fountaining (paroxysm) within less than four weeks, after a quiescent interval of 10.5 days (Fig. 1). This event, one of the most violent of the current series of paroxysms, was preceded by a long "prelude" (Strombolian activity) that started on the afternoon of 15 March, and was followed by weak, discontinuous activity at the Voragine.

Fig. 2. Strombolian activity at the NSEC (in the center) on the afternoon of 16 March 2013, seen from the area of Monte S. Leo, along the road from Nicolosi to the tourist area around the Rifugio Sapienza, on the south flank of Etna. At the left margin of the image, a part of the old SEC cone can be seen, and before it, the large pyroclastic cone of 2002-2003, whereas a part of the Montagnola is in the right foreground, with the shack hosting the monitoring cameras of the INGV-OE, visible and high-sensitivity visible ((EMOV and EMOH) and thermal (EMOT). Photo taken by Boris Behncke, INGV-Osservatorio Etneo.

During the days following the previous episode of lava fountaining at the NSEC, which had occurred on 5-6 March 2013, Strombolian activity continued at the Voragine, at first in numerous short but intense episodes; subsequently, this activity showed a slow diminution, and on 14 March, the seismic stations of the INGV-OE in the summit area showed only rare and weak signals indicating ongoing Strombolian activity. Sometime during the afternoon of 15 March, numerous explosion signals appeared on the seismic traces, and the volcanic tremor amplitude showed a slight, and rather slow increase, which continued in a very gradual manner through the evening of the same day. After nightfall, incandescence was visible at the NSEC, and inhabitants in nearby population centers (foremost Zafferana Etnea, on the southeast flank of the volcano) heard loud bangs coming from the crater. This activity continued during the night and through the following morning. At daylight on 17 March, numerous gas rings formed by the more powerful of the explosions were recorded by the monitoring cameras of the INGV-OE and photographed by observers in the field.

Fig. 3. Lava starts to overflow through the deep breach in the southeastern rim of the NSEC, shortly after 17:00 GMT (=local time -1) on 16 March 2013, seen from the"Piano del Lago", near the pyroclastic cone of 2001, on the upper south flank of Etna. Photo taken by Simona Scollo, INGV-Osservatorio Etneo.

Fig. 4. Lava fountain and eruption column charged with pyroclastic material seen from the provincial road 92 near Monte Vetore, on the south-southwestern flank of Etna, at 17:45 GMT on 16 March 2013. Also visible are the snow-covered Montagnola (at lower right) and the street lamps near the Rifugio Sapienza. Photo taken by Boris Behncke, INGV-Osservatorio Etneo.

Fig. 5. Lava fountain and eruption column about 2 km tall produced by the eruptive episode at the NSEC on 16 March 2013, seen from Randazzo, on the north-northwestern flank of Etna. The lava fountain clearly originates from a spot to the left of the cone of the Northeast Crater, at 3329 m the hightest point on the volcano. Photo taken by Marco Crimi and published here with kind permission by the author.

During the early afternoon of 16 March, the activity started to intensify more rapidly, and frequent jets of incandescent lava were launched up to 100-150 m above the crater rim (Fig. 2). About 17:00 GMT (=local time -1), lava started to overflow through the deep breach in the southeastern rim of the NSEC (Fig. 3). Approximately 15 minutes later, the explosions progressively became more energetic, throwing incandescent bombs onto the outer flanks of the cone; contemporaneously, the quantity of pyroclastic material (ash and lapilli) in the eruptive plume increased; this plume was blown by the wind toward southeast.

Between 17:30 and 17:45 GMT, the eruptive activity changed from Strombolian explosions to initially discontinuous lava fountaining, which strongly oscillated in height (from 50 to 300 m), and became more sustained after 17:45, though also after that time, there were sometimes significant oscillations in fountain height. The highest jets certainly rose 600-800 m above the crater rim, whereas the eruption column rose about 2 km above the summit of Etna before it was blown by the strong wind toward southeast. Around 18:00, several lightning flashes were observed within the eruptive cloud.

The entire cone of the NSEC and the adjacent areas to the south and southeast were subjected to a heavy downpour of large, incandescent bombs and scoriae; this precluded direct visual observation of a possible resumption of eruptive activity in the area of the "saddle" between the two cones of the Southeast Crater (SEC). However, observations made after the end of the paroxysm revealed that a lava flow was emitted from the area of the "saddle", though this lava flow appeared less voluminous and extensive than the lava flows emitted in the same area during the previous paroxysms. During the phase of most intense lava fountaining, numerous volcanic bombs fell onto the pyroclastic cones formed during the 2002-2003 eruption, up to 2 km from the NSEC. In this phase, the lava fountains were also spectacularly visible from the town of Randazzo, on the north-northeastern flank of Etna, about 15 km distant from the NSEC (Fig. 1, 5 and 6).

Heavy tephra fall, mostly in the form of scoriaceous lapilli, affected the southeastern slope of Etna; on the western headwall of the Valle del Bove this material was still incandescent. Further downslope, in the population centers of Zafferana Etnea, Santa Venerina and a number of villages to the north of Acireale, the tephra fallout formed a continuous deposit of scoriaceous lapilli, which in the northern portion of Zafferana Etnea locally was up to 10 cm thick. Many clasts in this area had diameters from 5 to 8, and more rarely, up to 10 cm, and numerous car windshields, skylights, and roof tiles were broken. Even on the Ionian coast, the deposit consisted largely of lapilli, with only a minor fraction of ash.

The first signs of a diminution in the eruptive activity became evident around 18:04 GMT, and at 18:10, the activity passed into violent explosions that ejected broad fans of numerous large, incandescent bombs, accompanied by loud bangs and detonations.

Fig. 6. Two photographs of the lava fountain from the NSEC on the evening of 16 March 2013, taken from Randazzo, on the north-northwestern flank of Etna. Photos taken by Elia Priolo and published here with kind permission by the author.

These explosions ceased at 18:20 GMT, but at 18:27 two particularly powerful explosions launched large incandescent rock fragments toward southwest to at least 1.5 km distance from the crater. A few weaker Strombolian explosions occurred shortly after 18:30 GMT.

At 03:49 GMT on 17 March 2013, a series of explosions started at the Voragine, which continued for about 5 minutes, generating strong thermal anomalies that were recorded by the thermal surveillance camera of the INGV-OE on the Montagnola (EMOT), probably accompanied by small ash puffs. During the next few hours, weak glows coming from the Voragine were recorded by the high-sensitivity visual monitoring camera on the Montagnola (EMOH). There were also small collapses and slides of still hot material from unstable portions on the NSEC cone, which generated minor quantities of ash.

Fig. 7. A panoramic view of the NSEC and its recent lava flows on the western slope of the Valle del Bove, photographed on the morning of 18 March 2013 from Giarre, on the lower east flank of Etna. The lava emitted during the 16 March 2013 paroxysm can be distinguished by its brown color from the earlier, black lavas. Note also the marked asymmetry of the NSEC cone, whose northern (right) rim is several tens of meters taller than its southern (left) rim. Photo taken by Turi Caggegi and published here with kind permission by the author.