Report on Etna (Italy) — 3 April-9 April 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 3 April-9 April 2013
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2013. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 3 April-9 April 2013. 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 on 3 April, after almost 18 days of relative quiet, the New Southeast Crater (NSEC) of Etna produced its ninth episode of lava fountaining. Activity had increased on 2 April when small grayish-brown puffs rose from NSEC. Cloud cover prevented further visual observations through the following night; however, sporadic glow suggested Strombolian activity. On the morning of 3 April, the volcanic tremor amplitude slowly increased and was accompanied by numerous explosion signals. Field observations revealed that at 1330 vigorous Strombolian activity was occurring at one or two NSEC vents, with jets of pyroclastic material rising up to a few tens of meters above the crater rim. The activity progressively intensified between 1400 and 1430, with frequent, powerful Strombolian explosions often generating loud bangs and launching great quantities of incandescent bombs (with diameters of many meters) onto the flanks of the cone. Shortly after 1435, ash emission started from the saddle vent (SV), followed a few minutes later by Strombolian explosions from the same vent. At 1450, a continuous jet of incandescent lava fountained up to 100 m, whereas the vents within NSEC continued to produce powerful loud explosions. At around 1505 a lava flow moved through the deep breach in the SE rim of NSEC and then traveled over the W rim of the Valle del Bove. During the same time interval, lava emissions started from SV, feeding a flow that went S.
Since 1430 the eruptive plume drifted SE and contained modest amounts of volcanic ash. At around 1540 ash emissions progressively increased and the volcanic tremor amplitude showed a rapid rise. Between 1540 and 1615 low lava fountaining continued from SV, whereas the vents within NSEC emitted intermittent, pulsating lava fountains. The incandescent jets from the vents within NSEC rose up to 400 m above the crater rim. At 1615, lava fountaining at SV intensified, with jets rising 400-500 m high. Explosions from the vents within NSEC continued, producing loud detonations every 1-2 seconds.
Lava fountaining significantly decreased between 1625 and 1628 when a new eruptive vent (NV) opened a few tens of meters to the W of SV, on the E slope of the old SEC cone, and emitted grayish-brown ash. A dense cloud of pyroclastic material emitted by NSEC vents and SV rose about 2 km high and drifted SE. Fallout of pyroclastic material affected almost the same area that had already been subjected to the heavy shower of lapilli on 16 March: Zafferana Etnea and Santa Venerina on the SE flank, and the N part of Acireale plus a number of smaller villages to the N at the S margin of Giarre, in the Ionian area. The deposit was thinner than that of 16 March, and the dimensions of the lapilli were notably smaller.
Between 1630 and 1640, the eruptive activity reached a new peak of intensity with sustained lava fountains from SV and powerful explosions from the vents within the NSEC. At 1637 a thermal surveillance camera recorded a pyroclastic flow from the NE flank of the NSEC cone. Two lava flows emerged from the same area and traveled toward the Valle del Bove.
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.