INGV reported that intense Strombolian activity began at Etna's Northeast Crater (NEC) during the evening of 17 May. Incandescent bombs were ejected above the crater rim and tephra was deposited on the flanks. During the morning of 18 May this activity was accompanied by ash emissions that drifted E and rapidly dispersed. Weak incandescence from the 25 November 2015 vent, on the upper E flank of the New Southeast Crater (NSEC) was visible, and an inclinometer about 1 km NW of NEC recorded rapid inflation of the summit area.

Just after 1250 on 18 May cameras recorded the onset of activity at Voragine (VOR) crater, which within a few minutes evolved into a pulsating lava fountain. At the same time Strombolian activity at NEC diminished and dark ash emissions formed briefly. Ash plumes from VOR rose as high as 3.5 km above the crater and drifted ESE. During the afternoon lava overflowed from the W rim of the Voragine-Bocca Nuova depression, and traveled W within the summit area. A second lava flow, emitted from a vent located at the E base of the Northeast Crater (NEC), expanded into the N portion of the Valle del Bove. The second lava flow remained active until the early morning hours of 19 May. Later that morning, the volcanic tremor amplitude sharply increased, and contemporaneously loud and virtually continuous bangs were heard in populated areas to the E and S of the volcano. A dense eruption plume drifted E at an altitude slightly higher than 1 km above the summit of Etna. Ash and lapilli fell onto the E flank of the volcano, near an area affected by the tephra fall on the previous day. A few hours later images revealed a new lava flow from VOR traveling W. Eruptive activity continued at least through 0900, though the volcanic tremor amplitude had diminished.

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)