INGV reported that strong activity at Etna’s Southeast Crater (SEC) included fountaining and lava flows on 21 December. Tremor amplitude had gradually increased on 20 December but weather conditions prevented visual observations. During the morning of the 21st Strombolian activity occurred at three vents. By 0800 tremor amplitude suddenly increased, and by 1000 lava fountaining from at least two vents was observed in thermal camera images, along with an eruption plume to 3 km (10,000 ft) a.s.l. [Correction: the eruption plume rose to 10 km (32,800 ft) a.s.l.] A lava flow emerged from the SW part of the cone, which had collapsed on 13 December, and traveled SW before branching W and E. A second flow from the NE side of the cone traveled E into the Valle del Bove. Lava fountaining ended around noon, with a simultaneous decrease in tremor amplitude. [Addition: An episode of lava fountaining occurred before sunrise on 22 December, producing lava flows that traveled SW, SE, and ENE.] During the morning of 22 December a few small phreatic explosions were visible in webcam images, likely generated from the interaction of snow and lava. The front of the active SW flow reached 2,500 m elevation. By 1741 both flows were cooling down and no longer advancing.

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)