Activity of the Sicilian volcanoes during December 2010

ETNA

After a very quiet period during the first three weeks of December 2010, Etna began to show renewed unrest during the last third of the month. Until 21 December, the volcanic activity consisted of the typical, deep-seated explosions within the conduit of the Northeast Crater. On windstill days, these explosions produced small puffs of vapor, and, occasionally, gas rings. Seismic signals characterizing the deep explosive activity as during the previous months occurred at intervals of a few minutes through the end of December.

On 22 December 2010 at 04:46:50 GMT, a strong explosion occurred at the western vent of the Bocca Nuova (BN-1). This event generated an ash plume a few meters high, which then moved into a northeasterly direction, causing light ash falls to as far as the town of Linguaglossa. Video recorded by the thermal camera of the Montagnola (EMOT) clearly show the emission of hot material with temperatures exceeding 60° C; a thermal anomaly is also evident in the footage recorded by the thermal camera of Nicolosi (ENT). However, the visible light footage recorded by other INGV monitoring cameras did not show any emission of incandescent material.

An analysis of ash sampled in different locations on the northeast flank of Etna (Linguaglossa, Piano Provenzana, e strada Mareneve fra Piano Provenzana e Rifugio Citelli) was carried out at the Laboratory of Sedimentology and Optical Microscopy (INGV-CT). The analysis showed that the ash consisted mainly of lithics whose content varied between 80  and 88%, most of the particles being altered, reddish material. The juvenile fraction was nearly exclusively constituted by tachylite, ranging from 6 to 14 % whereas sideromelane occurred in negligible amounts (max. 2 %). Furthermore, 4-5 % of the emitted particles were crystals.

The 22 December explosion was probably less powerful than the one on 25 August 2010, but certainly stronger than the numerous subsequent events between late-August and late-October. Smaller emissions of reddish-brown ash continued to occur during the forenoon of 22 December.

During the first few days, gas emission from the large pit crater on the lower east flank of the Southeast Crater cone nearly completely ceased. However, strong fumarolic activity continued from an extensive area on the upper east flank of the cone. On the afternoon of 23 December, bluish gas was emitted from the pit crater; inclement weather precluded further observations until 29 December. On that day, the pit crater was the source of extremely small emissions of incandescent material, which were recorded both by the Schiena dell’Asino visible camera (ESV) – after sunset –  and the Montagnola thermal camera (EMOT). These emissions were of extremely brief duration (2-6 seconds) and produced jets probably mainly consisting of hot gas, which barely rose above the rim of the pit crater. The source of the emissions corresponds to the open degassing vent observed during recent summit visits, which lies at the base of the western wall of the pit. During the last two days of the month, poor weather again precluded any observation of the activity.

STROMBOLI

Stromboli volcano is in a state of persistent eruptive activity, normally with explosions of medium to low intensity occurring from a number of vents located within the summit crater. During the month of December 2010, the activity continued with significant fluctuations, culminating in a powerful explosion on 19 December, and intense explosive activity at the end of the month.

On 19 December at 09:56:08 GMT, the vent labeled “S” in the southern part of the crater terrace produced an explosive sequence consisting of three events. The first explosion, which opened the sequence, ejected coarse-grained pyroclastics followed by more fine-grained material, to a height of more than 250 m above the crater terrace. After a few tens of seconds, a second, slightly less intense explosion occurred at 09:56:21. At 09:56:32 the third and last explosion occurred, which was weaker than the earlier two, with a pyroclastic jet reaching a height of 180-200 m. The fine-grained products (ash) of this sequence were dispersed over the W and NE sectors of the island. The thermal monitoring camera of the Vancori (SVT) has allowed to identify the three explosions more clearly than was possible from the Pizzo camera (SPT) footage, where the rapid succesion of the three explosions generated a superposition of the jets ejected by the second and third explosion and the falling material from the preceding events.

During the last few days of the month, vent “S1”, which lies immediately next to vent “S” (the source of the 19 December explosion), produced frequent explosions of greater intensity than those of the preceding days; some jets rose up to 200 m above the crater terrace. On 27 December, the frequency of such explosions reached 11-14 events/h.

VULCANO

Vulcano volcano is currently in a state of quiescence. During the month of December 2010, temperatures measured in fumaroles on the crater rim remained stable. No anomalies were observed in the geochemical parameters of the peripheral areas (soils in the Vulcano Porto areas and thermal aquifers).