Strong explosive eruptions were reported at Etna by INGV starting on 18 May after continuous degassing and moderate seismicity over the previous few days, with significant Strombolian activity and a paroxysmal event at SE Crater on 21 May. Views were often obscured by persistent weather cloud cover. Strombolian activity from SE Crater at 0456 on 18 May was seen in webcam images from the camera located at Montagnola. The Aviation Color Code was raised to Yellow (second lowest level on a four-color scale) at 1242 following a sudden increase in volcanic tremor amplitude that began at 1210. The signal amplitude decreased for a short time but then increased to an even higher level at 1330. A seismic swarm in the summit area at 1644 was immediately followed by ground deformation recorded at the Punta Lucia and Pizzi Deneri summit stations. At 1656 weak intra-crater Strombolian activity at SE Crater was observed in images taken by the INGV thermal camera at La Montagnola (3 km S). Explosive activity from Bocca Nuova crater starting at 1700 was visible in thermal images from the Bronte (13 km WNW) webcam, concurrent with infrasonic signals. The Aviation Color Code was raised to Orange at 1751. The activity likely persisted for a few hours based on satellite images; weather conditions prevented confirmation with webcams. Tremor fluctuated and by 0927 on 19 May levels had begun to decrease.

Intermittent explosive activity persisted at SE Crater during 19-20 May, with pulsating gas emissions rising from the crater. A sharp increase in volcanic tremors at 0720 on 21 May was a precursor to significant tall lava fountaining during 0730-1140, with ash plumes that rose to 10 km and drifted SW, S, and SE. At 0937 the Aviation Color Code was raised to Red after INGV field personnel observed ash and lapilli fall on the SW flank and ashfall in Adrano at 560 m elevation. Lava flows from SE Crater descended the W part of the Valle del Bove as far as 1.9 km E and the S flank as far as 2 km. Satellite data showed a large sulfur dioxide plume drifting E. Weather clouds prevented views of the activity. Tremor levels sharply decreased starting at 1135 and had stabilized by 1200. Ashfall was also reported in Catania and Aci Castello. According to news reports the ashfall caused the Catania-Fontanarossa Airport in Sicily to close until 0900 on 22 May. The runway had been covered in ash and at least 68 flights to and from the airport were cancelled.

The Aviation Color Code was lowered to Orange at 0601 on 22 May, though lava flows were still active. By 0832 on 23 May monitoring data indicated that eruptive activity had ceased, and webcam images showed that the lava flows were cooling. The Aviation Color Code was lowered to Yellow at 0840 and then to Green at 1051.

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.

Sources: Sezione di Catania - Osservatorio Etneo (INGV), Advanced geospatial Data Management Platform (ADAM), MSN