Fig. 3. Ash emission from the New Southeast Crater on the morning of 5 February 2013, seen from Tremestieri Etneo, on the southern flank of Etna. Photo taken by Boris Behncke (INGV-Osservatorio Etneo)

The most notable observation was the growth of the pyroclastic cone surrounding the eruptive vent that lies in the southeastern portion of the crater (Fig. 1). This cone has grown about halfway up the height of the inner crater wall, against which it is leaning; the growth in height above the elevation of the same vent at the beginning of the activity in July 2012 is at least 50-70 m. The entire crater floor is covered with recent lava (Fig. 2).

During the days following the 2 February 2013 eruptive episode (see the 2 February 2013 update), intermittent emissions of small quantities of ash were repeatedly observed both at the BN and at the New Southeast Crater (NSEC) (Fig. 3). On the evening of 5 February, the visual surveillance systems of the INGV-OE hanno showed a weak Strombolian activity at the NSEC, which continued until daybreak on the next day, and then became invisible due to the deteriorating weather conditions.

Evidence for the 6 February eruptive episode at the BN is based exclusively on seismic data, foremost the volcanic tremor, and on infrasound, showing an instantaneous increase starting at 09:20 GMT (=local time -1). The volcanic tremor amplitude rose to a peak within a few minutes from the start of the activity, and began to descend after less than one hour. In terms of seismic energy release, this episode seems to have been slightly more intense than its two predecessors. People who were in the skiing area on the northeast flank of the volcano briefly saw a dense but ash-free gas plume rising from the summit.

Fig. 4. Frame extracted from video recorded by the high-sensitivity visual surveillance camera of the INGV-Osservatorio Etneo (Catania) on the Montagnola  (EMOH) during the phase of most intense activity of the eruptive episode on 8 February 2013 at the Bocca Nuova. Note the gas plume brightly reflecting the glow of the incandescent lava jets

Again, the interval of relative calm after the 6 February eruptive episode was characterized by sporadic ash emissions mostly from the NSEC. Visual observations of the activity were often severely hampered by the poor weather conditions, but on the evening of 8 February, weak glows were intermittently visible at the NSEC. At 20:00 GMT, high-sensitivity visible surveillance camera of the INGV-OV on the Montagnola (EMOH) recorded the appearance of fluctuating glows coming from within the BN; during the next 10 minutes, the glow became continuous. Around 20:25 GMT, jets of incandescent lava were repeatedly seen to rise above the thick blanket of clouds drifting over the summit area of Etna. Contemporaneously, the volcanic tremor amplitude showed the usual sharp rise, but peaking at a slighly lower amplitude compared to the previous episode. After 21:00 GMT, the volcanic tremor amplitude began to decrease, whereas the eruptive activity continued without showing signs of diminishing for another about 30 minutes (Fig. 4).

The time of conclusion of the 8 February episode is not well constrained, because after 21:30 GMT, cloud cover systematically hindered visual observation. During the interval of 9-10 February, the summit area of Etna was almost constantly covered by dense cloud cover; the only visible sign of activity during these days was a brief ash emission on the morning of 10 February.

Fig. 5. Frame extracted from video recorded by the visible-light monitoring camera at 400 m altitude on Stromboli (SQV) during the emission of a small lava flow onto the northern flank of the Sciara del Fuoco at 00:22 GMTon 9 February 2013.

Stromboli: resumption of intermittent effusive activity. After about three weeks of normal explosive activity, new, small overflows have started from the crater terrace of Stromboli. The first overflow started on the late forenoon of 8 February, producing a small lava flow that descended the upper northwestern slope of the Sciara del Fuoco, and ceased during the afternoon of the same day. The second overflow, which took a path directed due north, began shortly after midnight between 8 and 9 February. Observation of the phenomenon was interrupted after 00:25 GMT on 9 February due to rather bad weather, which interrupte the transmission of the video signals recorded by the surveillance cameras of the INGV-OE at 400 m elevation. When video transmission resumed shortly after 09:00 GMT, feeding of the lava flow had diminished, and the active flow front was retreating upslope, generating frequent rockfalls.

In the late afternoon of 9 February, lava effusion ceased altogether, but resumed once more during the early morning hours of 10 February, generating a small flow that slowly advanced downslope for a few tens of meters. The lava front continuously disintegrated spawning incandescent rockfalls. During the day, lava emission progressively diminished, and ceased completely in the late afternoon.