Etna update, 2 February 2013

Fig. 1. Strombolian activity at the New Southeast Crater at 03:25 GMT (=local time -1) on 2 February 2013. Photo taken from Pedara (southeast flank of Etna) by Marco Di Marco (EtnaWalk) and published here with kind permission by the author

Etna: New eruptive episode at the Bocca Nuova. During the early morning hours of 2 February 2013, after little more than two days of relative calm, Etna's Bocca Nuova (BN) produced a new episode of intense intracrater Strombolian activity. Since the onset of the latest period of episodic summit activity, on 10 January 2013, 6 episodes of Strombolian activity and small lava fountains have taken place at the Bocca Nuova, and two Strombolian episodes at the New Southeast Crater (NSEC). As has already happened during the 28 January episode, the activity at the Bocca Nuova on 2 February was preceded and accompanied by intermittent, weak Strombolian activity at the NSEC (Fig. 1).

During the interval of relative quiescence following the 30 January eruptive episode, ash emissions occurred repeatedly at the NSEC (on 31 January and on 1 February) and at the BN (only on 1 February). At the NSEC, ash emission was nearly continuous for intervals lasting from a few minutes to more than one hour, whereas the BN emitted ash in discrete, small puffs. In all cases, the ash plumes rose no more than 100 m above the crater rims.

Shortly after 02:00 GMT (=local time -1) on 2 February, the high-sensitivity visible surveillance camera of the INGV-OV on the Montagnola (EMOH) started to record intermittent weak glows coming from the NSEC; after 02:30 GMT, sporadic small explosions launched incandescent pyroclastic material up to a few tens of meters above the crater rim, also generating small anomalies in images recorded by the thermal surveillance camera of the INGV-OV on the Montagnola (EMOT) (Fig. 2a, b). The strongest explosions occurred at 02:45, 03:00, 03:09 and 03:11 GMT, which ejected glowing bombs onto the flanks of the NSEC cone. Two minutes after the latest of these explosions, a dull glow appeared at the BN, which lasted only for a short time; however, during the following 30 minutes, intermittent glows were recorded at both the BN and the NSEC.

Fig 2. Frames extracted from video recorded by the high-sensitivity visual surveillance camera of the INGV-Osservatorio Etneo (Catania) on the Montagnola  (EMOH) and the thermal camera on the Montagnola (EMOT), during the 2 February 2013 eruptive episode at the Bocca Nuova (BN) and New Southeast Crater (NSEC); all times are GMT (=local time -1). (a) 03:11, incandescent bombs are launched from the NSEC; (b) 03:21, thermal anomaly at the NSEC recorded by EMOT; (c) 04:22, increasing activity at the ìBN (center) and small Strombolian explosions at the NSEC (at right); (d) 04:45, strong thermal anomaly caused by lava fountaining at the BN recorded by EMOT; (e) 04:51, lava fountain at the BN and absence of activity at the NSEC; (f) 05:17, lava fountain from the BN shortly before the activity began to diminish.

Around 03:50 GMT, the first jets of lava rising above the rim of the BN were recorded, and from 04:00 onward, Strombolian activity was essentially continuous, with frequent jets up to many tens of meters above the crater rim. In this interval, the NSEC showed no glows, but at 04:12 GMT small Strombolian explosions resumed at this crater. Shortly after 04:15, activity at the BN started to increase rapidly; contemporaneously, the volcanic tremor amplitude showed a sharp rise. At the same time, small Strombolian explosions continued at the NSEC (Fig. 2c). As during the preceding episode, the activity within the BN gradually took on the character of a pulsating but continuous lava fountan, and often the lava jets rose 120-150 m above the crater rim (Fig. 2d). Activity at the NSEC started to diminish after 04:30 GMT and ceased altogether shortly before 05:00 (Fig. 2e); at the BN the activity continued vigorously with the first daylight (Fig. 2f), but then showed a marked diminution between 05:20 and 05:30, which was also evident from the rapid descent of the volcanic tremor amplitude. With growing daylight, the glow at the Bocca Nuova became invisible, and it is possible that weak intracrater activity continued for a few more hours; however, by 08:00 GMT the episode was definitely over.

Once more, the source of Strombolian activity and minor lava fountaining at the Bocca Nuova was the vent sitting at the southeastern base of the inner crater wall, which has been the site of numerous eruptive episodes in the past seven months. Lava emission during each of these episodes has led to the progressive filling of the deeper portions of the crater floor, as has been ascertained during field visits carried out by INGV-OE staff on 27 January and by M. Mammino on 1 February 2013. The lava that has accumulated on the crater floor has completely filled all depressions that were present before the start of eruptive activity in July 2012, and its level is approaching the crest of the rocky septum separating the BN from the adjacent Voragine.