Sezione di Catania - Osservatorio Etneo reported that the seventeenth paroxysmal eruptive episode of 2011 took place at the New SE Crater (New SEC) of Etna during the evening of 23 October. Weak explosive activity was recorded at 1913, and at about 1935 small anomalies appeared in images recorded by thermal cameras. Explosive activity rapidly intensified at 1940 and by 2007 that crater was completely filled with lava. The lava overflowed through a breach in the E crater rim and traveled towards the Valle del Bove.

At 2026, Strombolian activity transitioned to continuous lava fountains that rose a few tens of meters above the crater rim. At 2036, a vent opened on the SE flank of the cone, producing a second lava fountain, leading to a significant increase in the lava effusion rate. The height of the lava fountains significantly increased after 2100, reaching 300 m above the crater. At about 2130, a third vent became active within the New SEC, possibly near the N rim. Abundant amounts of tephra fell on the E flank of the cone, forming a dense curtain, while large incandescent blocks rolled to the base of the cone on more gently sloping terrain. At approximately 2229 two lightning flashes near the crater were observed. After 2230 both effusive and explosive activity showed a marked reduction, changing again into Strombolian activity around 2300, and ceasing altogether at 2315.

The lava flow continued to advance towards the Valle del Bove until about 0040 on 24 October and stagnated just upslope of Monte Centenari (at 1,900 m a.s.l.). The area most heavily affected by the tephra (ash and small scoriaceous lapilli) fall was the E flank of Etna, including the N portion of the towns of Zafferana (about 10 km to the E), Milo (about 11 km ESE), and Fornazzo (10 km E), downslope across Santa Venerina (SE flank) and Dagala del Re (14 km ESE) to Giarre (~17 km E) and Riposto (18 km E), as well as nearby villages.

Geological Summary. Mount Etna, towering above Catania on the island of Sicily, has one of the world's longest documented records of volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Source: Sezione di Catania - Osservatorio Etneo (INGV)