Sezione di Catania - Osservatorio Etneo reported that the eleventh lava-fountaining episode of 2013 began at Etna's New Southeast Crater (NSEC) on 18 April. Activity increased on 16 April with ejected incandescent tephra and small ash puffs from a vent inside NSEC, followed by weak Strombolian explosions. Strombolian explosions became more frequent and intense on the morning of 18 April and then were almost continuous by 1300. During the next two hours lava fountains developed and a dense plume drifted SSW. Ash and lapilli fell in between the villages of Ragalna, Belper, and Paterno, as well as the tourist area "Etna Sud." Lapilli-fall was a few centimeters deep and clasts were at most 5 cm in diameter. Three lava flows were produced; the largest flowed through the deep notch in the SE rim of the crater and traveled 4 km towards the Valle del Bove. The interaction of the lava with snow led to rapid melting, generating small lahars. The two other lava flows originated in the saddle between the two SEC cones; one traveled N and the other S. After the lava fountains ceased, strong explosions were heard the rest of the day. On 19 April explosions produced little puffs of ash and ejected hot tephra.

The twelfth episode occurred two days later during the late afternoon of 20 April. Intermittent explosions ejected incandescent tephra and generated small ash puffs on 19 April. During the evening a large dark plume rose from NSEC, and sporadic Strombolian explosions were observed. The explosive activity ceased in the late evening, but shortly afterwards the lower of the two effusive vents at the base of the NSEC cone produced a lava flow that traveled 1.5 km towards the Valle del Bove. Around 1700 ash puffs rose from the crater, followed by incandescent tephra ejected at 1713. Within a few minutes sustained lava fountains were observed, along with a tall eruption plume that drifted E. Ash and lapilli fell over a wide area to the E, including along the Ionian coastline, just S of Guardia Mangano, up to Fiumefreddo, including the towns of Taormina, Ripon, and Mascali, and further upstream, including Santa Venerina, Zafferana, Milo, and Sant'Alfio.

On 20 April several lava flows on the W wall of the Valle del Bove interacted with the snow, generating explosions and lahars. Around 1815 lava-fountain activity decreased and turned into explosions and ash emissions. At 1840 the paroxysm was over. In the evening, the lava flow emitted from the effusive vent at the base of the SE part of the NSEC cone was still well-fed. Poor weather conditions prevented visual observations until the evening of 21 April, when surveillance videos showed sporadic Strombolian explosions accompanied by small ash puffs at the NSEC, and the emission of a small lava flow from the base of the cone.

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)