INGV reported that activity at Etna’s summit craters continued during 29 July-4 August. On 29 July ongoing Strombolian activity at the Voragine crater generated a small ash emission that quickly dispersed from the summit area. Around 0408 on 4 August the Strombolian activity at Voragine crater began to increase in intensity and frequency, with volcanic tremor amplitude reaching very high levels around 0430 and increasing further by 0520 when activity transitioned to lava fountains. At 0445 the Aviation Color Code was raised from Orange to Red, though the ash cloud height could not be estimated. The fountains produced an SO2-rich eruption plume that by 0542 had reached about 6.5 km above the summit (to about 10 km a.s.l.) and was drifting SE; significant tephra (ash and lapilli) fell towards the E, affecting areas such as Fleri (14 km SE), Fornazzo (10.5 km E), Zafferana (11 km SE), Milo (11 km ESE), Santa Venerina (14 km SE), Giarre (17 km E), Riposto (18 km E), Stazzo (20 km SE), Torre Archirafi (20 km E), San Giovanni La Punta (20 km SSE), Viagrande (17 km SE), Aci Sant'Antonio, Aci Catena (20 km SE), Aci Castello (23 km SE), Aci Trezza (23 km SE), and Acireale (20 km SE). An ash advisory at 1058 noted that a second plume with a high ash concentration had reached 6.2 km a.s.l., and both it and the higher plume were drifting SSE. The high tremor amplitude decreased after 0910, explosive activity decreased over the next few hours, and at 1318 the Aviation Color Code was lowered from Red to Orange, though there were still sporadic emissions with ashfall confined to the summit area. Operations at the Aeroporto de Catania were reduced to six arrivals per hour during part of this period of elevated activity. During the lava fountaining, INGV observers noted that lava from Voragine had completely filled the Bocca Nuova (BN) crater, resulting in lava overflows from its W rim. There was an also an active flow moving NW to an elevation of about 3,000 m, and a flow was present between the Voragine and BN craters.

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), Toulouse Volcanic Ash Advisory Centre (VAAC), Aeroporto di Catania