The previous report on Mount Etna (BGVN 30:01) described what turned out to be the final activity of the 2004-05 eruption, which ended by March (Burton and others, 2005). From March 2005 until November there was only a low and quiet degassing at the summit craters. Between the end of November and early December 2005 a significant increase in the SO₂ output was accompanied by an increase of volcanic tremor and a minor deformation of the summit part of the volcanic cone.

On 16 December 2005 an explosive sequence was recorded by the INGV-CT seismic network, localized at the summit. This was accompanied by an increase in SO₂ emission, which reached peaks 10 times the background flux levels. On 22 December the increase in gas pressure was accompanied by a dilute emission of juvenile ash from the Bocca Nuova crater. This vent had been blocked since the end of the previous summit eruption. However, the very fine-grained nature of the ash suggested a deep level of the magma column within the conduit.

Reference. Burton, M., Neri, M., Andronico, D., Branca, S., Caltabiano, T., Calvari, S., Corsaro, R.A., Del Carlo, P., Lanzafame, G., Lodato, L., Miraglia, L., Muré, F., Salerno, G., and Spampinato, L., 2005, Etna 2004-05: an archetype for geodynamically-controlled effusive eruptions: Geophysical Research Letters, v. 32, L09303, doi:10.1029/2005GL022527.

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.

Information Contacts: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/).