Report on Etna (Italy) — 10 April-16 April 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 10 April-16 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, 10 April-16 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 the tenth eruptive episode of 2013 began at Etna's New Southeast Crater (NSEC) on 8 April with sporadic ash emissions occasionally accompanied by incandescent material. A large explosion at 2252 was heard up to 15 km away. The ash emissions continued for about 48 hours. In the late afternoon on 10 April Strombolian activity began, producing minor ash emissions during some of the explosions. In the morning on 11 April Strombolian explosions occurred about every 2-5 seconds, ejecting incandescent pyroclastics several tens of meters above the crater rim. Strombolian activity increased slowly in intensity and frequency of explosions throughout the day; contemporaneously the volcanic tremor amplitude continued to show a gradual rise. Late in the afternoon frequent and very powerful Strombolian explosions occurred every 1-2 seconds and were widely audible around the volcano. Jets of incandescent pyroclastics often rose 200 m above the crater rim and generally contained minor amounts of ash. Around 1840, a small amount of lava flowed over the deep breach in the SE rim of the crater. In the late evening it stopped and showed evidence of cooling.
Around 0110 on 12 April another small lava flow traveled S then SE from the saddle between the two cones of the Southeast Crater (SEC). Throughout the night powerful explosions alternated with intermittent, low lava fountains. At daybreak on 12 April a dense eruption plume containing relatively minor amounts of pyroclastic material drifted ESE. Until about 1025 on 12 April, all eruptive activity occurred exclusively at one or two closely spaced vents within the NSEC, then lava was emitted from two vents at the NE base of the NSEC cone. At 1024 a flow of hot pyroclastic material from the same area traveled about 2 km NE in less than 1 minute.
In the meantime, eruptive activity continued at the NSEC with frequent, powerful Strombolian explosions and emission of modest quantities of volcanic ash, which was rapidly dispersed. Lava emission from the SSE rim of the NSEC, the saddle, and the NE base of the cone remained active. Shortly before 1200, the eruptive activity changed from low lava fountains to Strombolian explosions and intermittent ash emissions. Vigorous ash emissions resumed at 1214 both from the main vent of the NSEC and from the saddle vent. Expulsion of blocks, bombs and ash from the saddle vent continued until 1234, when the main vent of the NSEC reactivated, and for the next nearly 20 minutes both vents were the source intense ash emissions.
The activity shifted back entirely to NSEC, entering into the true paroxysmal phase of this episode at 1250 with sustained lava fountaining, accompanied by a return to high levels of the volcanic tremor amplitude. During the following 10 minutes, there was a considerable increase in the quantity of pyroclastic material in the plume, which drifted ESE. Tephra fall (ash and small lapilli) affected Fleri, Zafferana Etnea, Milo and S. Maria la Scala, although the quantity of fallout was much smaller compared to those of the previous paroxysms. Sustained lava fountaining continued for about one hour; a few minutes after 1400 the activity switched to sporadic Strombolian explosions and ash emissions, which gradually diminished in vigor. During 1400 and 1410, repeated collapses occurred on the SE flank of the NSEC cone, possibly from new vents at the base of the cone, from which a new lava flow traveled toward the Valle del Bove. The collapses generated avalanches and clouds ash. Explosive activity progressively diminished and completely ceased around 1700.
On the evening of 12 April, the lava flows emitted from the saddle and from the various vents on the flanks of the cone were incandescent and slowly moving; during the night, the surveillance cameras showed the cessation of all lava emission and the cooling of the flows. However, on the morning of 13 April, slow lava effusion resumed from the lower of the vents and a small flow advanced a few hundred meters. This flow ceased in the early morning hours the following day. Once more, on the evening of 14 April, there was a rather weak resumption of effusive activity from this vent, which ceased after a few hours.
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.