Report on Etna (Italy) — 14 March-20 March 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 March-20 March 2012
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2012. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 14 March-20 March 2012. Smithsonian Institution and US Geological Survey.
37.748°N, 14.999°E; summit elev. 3295 m
All times are local (unless otherwise noted)
Sezione di Catania - Osservatorio Etneo reported that the twenty-second paroxysmal eruptive episode since January 2011 took place at New SE Crater (New SEC) of Etna during the morning of 18 March following two weeks of quiescence. Roaring from high-pressure degassing was heard on 16 March. The next day there was incandescence and multiple vapor clouds with minor ash content that rose from New SE Crater. In the early hours of 18 March the incandescence intensified due to Strombolian activity on the crater floor, and volcanic tremor amplitude rapidly increased. Strombolian activity continued to intensify, and just before 0700 lava flowed through the deep breach in the SE crater rim. At about 0825 the ash content in the gas plume rising from the crater became more significant and pulsating lava fountains from a vent on the crater floor rose about 100 m high. Shortly before 0900 two vents were active within the crater and a jet of lava was emitted from another vent within the breach in the SE crater rim.
During 0900-0915 lava fountaining was essentially continuous from all three vents. An intense shower of coarse-grained pyroclastic material falling onto the N and NE flanks of the cone generated avalanches and clouds of rock and dust, which traveled to the base of the cone. A plume rose 4-5 km above Etna and drifted E. Ash and lapilli fell mainly in the area between the villages of Zafferana Etnea and Sant'Alfio, extending toward the Ionian Sea between Riposto and Pozzillo.
The main lava flow descended the steep W slope of the Valle del Bove. Several lava lobes, however, took a more northerly path to areas covered with thick snow. The interaction of the lava and snow led to rapid melting of the snow, generating small lahars, and strong explosions that produced ground-hugging vapor-and-ash clouds resembling pyroclastic flows, which repeatedly descended on the floor of the Valle del Bove. The vapor-and-ash clouds rose 1-1.5 km above the floor of the Valle del Bove. This phenomenon continued intermittently for some time after the cessation of the lava fountaining and ash emission, until about 1130.
Lava fountaining and strong ash emission continued without significant variations until about 1040; afterwards the activity rapidly diminished in intensity, and the last ash clouds were observed around 1110. Similar to the previous episodes, the lava that flowed through the breach in the SE crater rim advanced for several hours after the cessation of the paroxysmal activity into the upper part of the Valle del Bove. The lava reached a distance of about 4 km from the source, stagnating S of Monte Centenari. A small lava flow, emitted from a fracture on the N flank of the cone, followed the same path as a flow emitted from the same fracture during the 4 March paroxysm, and traveled a few hundred meters.
Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical 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 horseshoe-shaped 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.