The 1 April 2012 paroxysm of Etna
Figure 1. Strombolian activity and beginning of lava overflow through the breach in the southeastern rim of the New Southeast Crater, shortly after 01:00 GMT (= local time -2), 1 April 2012. The view is from Piano del Vescovo on the southeast flank of Etna. Photo taken by Paola Garofalo and published here with kind permission of the author (original version on Flickr)
During the early morning hours of 1 April 2012, a new episode of lava fountaining (paroxysm) occurred at the New Southeast Crater (New SEC) of Etna, the 23rd episode in the ongoing sequence that began in January 2011, and the 5th of this year (Figure 1). This event took place nearly two weeks after its predecessor, and was once more characterized by tall lava fountains, a column of tephra and vapor several kilometers high leading ash and lapilli falls in the southeastern sector of the volcano, and lava flows that descended into the Valle del Bove, locally interacting with the thick snow cover on the ground.
From 26 March onward, the monitoring cameras of the INGV-Osservatorio Etneo showed intense pulsating degassing from the New SEC, and at 11:02 GMT (= local time -2) on 30 March 2012, an emission of dark gray ash was observed, which formed a small plume rising about 250 m above the crater.
Figure 2. Small Strombolian explosion at the New Southeast Crater seen from Trecastagni (southeastern flank of Etna) on the evening of 31 March 2012. Photo taken by Boris Behncke, INGV-Osservatorio Etneo (Catania) |
Similar ash puffs occurred at intervals of a few minutes, producing minor anomalies in the images recorded by the thermal cameras on the Montagnola (EMOT) and at Monte Cagliato (EMCT). After sunset, weak and sporadic Strombolian activity was visible within the crater, which continued - with significant fluctuations in the frequency and intensity of the explosions - for the whole night. This activity was accompanied by a slight increase in the volcanic tremor amplitude. On 31 March, the activity continued at rather low levels, with fluctuations in the volcanic tremor amplitude; on the evening, vivid though still weak Strombolian activity was visible (Figure 2). Starting at 01:30 GMT on 1 April, the frequency and intensity of the Strombolian explosions increased, accompanied by a rise in the volcanic tremor amplitude. A small lava flow exited through the deep breach in the southeastern rim of the crater, reaching the base of its cone after about 30 minutes, where it divided into two parallel lobes. Around 02:00 GMT, the Strombolian activity passed into lava fountaining and abundant ash emission, forming an eruption column that rose several kilometers above the summit. In the meantime, the lava flow advanced in several parallel lobes, rapidly spilling down the steep western slope of the Valle del Bove (Figure 3). The eruptive plume was blown by the wind toward the southeastern sector of the volcano, leading to heavy falls of ash and lapilli in the areas between Zafferana Etnea and Monterosso, and further downslope, between Giarre and Acireale, forming a continuous deposit (Figure 4). |
Figure 3. In the most intense moments of the lava fountaining episode of 1 April 2012, the New Southeast Crater cone was completely covered with incandescent pyroclastic material, while two main lava flows spilled down the steep western slope of the Valle del Bove. The dense vapor and ash cloud in the left portion of the image is the result of strong explosive interaction between lava and snow, a phenomenon quite common during paroxysmal episodes during the winter season. Photo taken at Caselle (just north of Zafferana Etnea) by Boris Behncke, INGV-Osservatorio Etneo (Catania)
During the most intense phase of lava fountaining, the breach in the southeastern rim of the crater was widened on its northern side, allowing the formation of a new lava flow to the north of the flow already advancing. Along both flows, intense explosive interaction between lava and snow was observed repeatedly, which generated small, ground-hugging clouds of ash and vapor as well as lahars, and vertical columns of vapor and ash - phenomena that have been observed also during some of the earlier paroxysmal episodes such as 10 April 2011, and 4 and 18 March 2012.
Figure 4. In the area between Zafferana Etnea and Monterosso, on the southeast flank of Etna, the pyroclastic fall deposit (ash and lapilli) was continuous, as seen in this image showing the main road of Sarro (S.P. 148) at daybreak on 1 April 2012. Photo taken by Boris Behncke, INGV-Osservatorio Etneo (Catania) |
The ground-hugging ash and vapor clouds strongly resembled, in their aspect and movement, pyroclastic flows, though for their mechanisms of formation and temperature these flows are certainly different from "classic" pyroclastic flows. Lava fountaining and strong ash emission continued without significant variations until about 03:30 GMT, after which the volcanic tremor amplitude started to diminish, and the lava fountains passed into Strombolian explosions and ash emission at decreasing intensity. All eruptive activity was essentially over by about 04:40 GMT. For several hours following the cessation of eruptive activity, the two main lava flows continued to advance downslope, the more southerly being the longer of the two, without, however, reaching the extent of the 18 March lava flows. On the evening of 1 April, the New SEC cone still showed numerous incandescent spots, due to small slides and rockfalls of the still-hot pyroclastic deposit covering the cone. The 1 April episode occurred after a relatively calm interval of little less than 14 days, similar to the interval that had separated the previous two (4 and 18 March) paroxysmal episodes. The volume of lava emitted in this latest episode was clearly inferior to that of the preceding episodes. Furthermore, no lava emission was observed from the northern and southern flanks of the cone. The morphological changes to the cone caused by the latest paroxysm are relatively unconspicuous; the cone has slightly grown in elevation on the southern and northern rims of the crater, and the breach cutting the southeastern crater rim has become wider, showing two parallel lava overflow channels. |