Etna and Stromboli update, 15 January 2013

Fig. 1. Strombolian activity at Etna's Bocca Nuova on the evening of 12 January 2013, seen from Tremestieri Etneo on the south flank of the volcano. Incandescent bombs are rising several tens of meters above the crater rim. To the right is the (old) cone of the Southeast Crater. Photo taken by Boris Behncke (INGV-OE)

Fig. 2. These frames extracted from video recorded by the high-sensitivity surveillance camera of the INGV-Osservatorio Etneo (Catania) on the Montagnola  (EMOH), in the moment of a particularly strong explosion on the evening of 14 January 2013 (top), and on the early morning of 15 January 2013 (bottom), shortly before the cessation of the Strombolian activity, when clouds over the summit of Etna were illuminated by the last glows.

Etna: cessation of activity at the Bocca Nuova. The intense Strombolian activity within Etna's Bocca Nuova, which started early on 10 Jnuary 2013, continued for five days and then ended during the early morning hours of 15 January. At night during the past few days, in conditions of good visibility, the activity was well visible from population centers around the volcano (Fig. 1); often the jets of incandescent bombs rose many tens of meters above the crater rim. On the evening of 14 January, the activity was particularly intense, with jets that reached about 100 m above the crater rim (Fig. 2, top). Durning the early hours of 15 January, the high-sensitivity visual surveillance camera of the INGV-Osservatorio Etneo on the Montagnola (EMOH) continued to record vigorous activity; in spite of clouds starting to hover around the summit, strong glows were recorded until about 04:00 GMT (=local time -1) (Fig. 2, bottom). This latest episode of intracrater eruptive activity at the Bocca Nuova has been, in its main characteristics, very similar to those that had occurred between July and October 2012, with Strombolian activity from a single vent located at the southeastern base of the inner crater wall. Although no direct observations of the activity were made from the crater rim, it is almost certain that the Strombolian activity was accompanied by the emission of lava onto the crater floor, as has been the case also during the previous episodes. Stromboli: continued lava overflows from the crater terrace. In the past few days, there have been further intermittent lava overflows from the crater terrace of Stromboli, with characteristics essentially similar to those of the previous overflows (see the 10 January 2013 update). After several days with only minor lava emission from the northeastern rim of the northernmost vent on the crater terrace, a more voluminous overflow started in the early morning hours of 12 January (Fig. 3, top frames), reaching the coastline after a few hours.

Fig. 3. Images recorded on 12 January 2013 by the visual surveillance camera at 400 m elevation on Stromboli (SQV). The first two frames show the initial evolution of a new lava overflow from the crater terrace at daybreak, accompanied by quasi-continuous spattering from a vent in the northern part of the crater terrace, and explosions from two other vents in the northern and southern portions of the crater terrace. The images at center show the dense vapor and ash cloud generated by the largest landslide sequence in the late forenoon; the right frame shows a dense curtain of falling ash. The bottom frames show the eruptive activity in the late afternoon, with intense Strombolian activity and development of a small lava overflow only a few tens of meters long.

During the late forenoon, numerous small landslides were observed, generated by the sliding and rolling of loose and unstable material on the steep slope of the Sciara del Fuoco, mixed with fragments of still hot lava. A somewhat larger landslide sequence started at 11:10 GMT, producing a dense, dark cloud of vapor and ash that rose from the lower portion of the Sciara dn was blown by the wind upward toward the summit and then over the village of Stromboli, clouding the images transmitted by the visible surveillance camera at 400 m elevation of the INGV-Osservatorio Etneo (Fig. 3, center). The vapor and ash cloud was observed and photographed by numerous eyewitnesses in the village. The phenomenon was accompanied by a rapid increase in the volcanic tremor amplitude recorded on all seismic stations of the INGV on the island, which lasted about 16 minutes but did not correspond to any variation in the eruptive activity, at least as far as the northern vents on the crater terrace were concerned. The intense emission of vapor, which produced a cloud heavily charged with fragmented volcanic material, was the result of the wholesale collapse into the sea of a sizeable portion of the still-hot lava on the slope of the Sciara; this reconstruction was confirmed also during a helicopter flight over the Sciara del Fuoco (Fig. 4) on the morning of 13 January.

Fig. 4. The Sciara del Fuoco of Stromboli photographed during the helicopter overflight on the morning of 13 January 2013; note the streak of light-colored material, corresponding to the area of landsliding on the previous day. Photo taken by Mauro Coltelli (INGV-OE)

Following the major landslide sequence, vigorous Strombolian activity continued on the crater terrace, and at nightfall, a rather small active lava flow was visible in the uppermost portion of the  (Fig. 3, bottom frames); this flow ceased completely on the late evening of 12 January.

On the late evening of 13 January, renewed lava effusion started to produce an overflow toward northwest (Fig. 5), which continued in a pulsating manner through the night, intensifying notably after 03:30 GMT on 14 January.

Fig. 5. Development of a new lava overflow on the late evening of 13 January 2013, recorded by the visual surveillance camera at 400 m elevation on Stromboli (SQV). The left frame shows huge incandescent blocks detaching from the front of a small lava flow and rolling down the Sciara del Fuoco; the frame at right shows the lava flow lengthening downslope on the medium-upper portion of the Sciara.

Around 04:20 GMT on 14 January, a second lava lobe developed next to the already active flow, but further to the north, reaching a length of about 100 m (Fig. 6, top left); after one hour, the lobe was no longer fed and started cooling. The main lava flow, however, continued its downslope movement without significant variations, and around 06:20 GMT another overflow began to take the same path as the small lobe of 04:20 GMT. This time supply of lava to the flow was rather vigorous, forming a fan-shaped lobe (Fig. 6, top right), which descended rapidly next to the earlier main flow. During the daylight hours, interaction of hot material from the lava flow and sea water generated dense vapor clouds, mixed with ash generated by numerous small landslides; these phenomena reached their maximum intensity during the early afternoon. At dusk, three lava flows were active on the upper slope of the Sciara (Fig. 6, bottom left); of these, only one remained active on the late evening (Fig. 6, bottom right).

Fig. 6. Effusive activity on 14 January 2013, recorded by the visual surveillance camera at 400 m elevation on Stromboli (SQV) at daybreak (top frames), on the late afternoon (bottom left) and on the evening (bottom right).

At daybreak on 15 January, only a small lava flow was active (Fig. 7, left), but on the afternoon the effusion rate once more increased, feeding a flow that was well visible at sunset (Fig. 7, right).

Fig. 7. Effusive activity on 15 January 2013, recorded by the visual surveillance camera at 400 m elevation on Stromboli (SQV) at daybreak (left) and on the late afternoon (right).