Activity of the Sicilian volcanoes during August 2010
ETNA
During the month of August 2010, Etna has shown increasing signs of unrest. On 8 August, shortly before noon (local time = GMT+2), a minor ash emission occurred from the active western pit (BN-1) of the Bocca Nuova, the westernmost of the four summit craters of Etna. This emission was probably caused by collapse of a portion of the unstable crater wall.
Throughout the month, deep-seated explosions within the open inner pit on the floor of the Northeast Crater have continued, producing loud booms and prolonged rumbling and hissing sounds, which were well audible during visits to the summit made by INGV-Catania staff and the Etnean mountain guides. Field observations revealed that no new eruptive products have been emplaced, neither outside nor within the visible portion of the Northeast Crater.
Starting at 15:09 h on 25 August, a series of ash emissions occurred from the BN-1 vent of the Bocca Nuova, lasting until 15:23 h. The onset of these emissions was strongly explosive, emitting hot gas for a few seconds, as recorded by the visible and thermal monitoring cameras at the Montagnola (about 3.5 km south of the Bocca Nuova). The Montagnola thermal camera recorded thermal anomalies of up to 170° C during the first moments of the explosion, which also generated a visible shock wave. A column of dark gray ash rose about 1-2 km above the summit of Etna before drifting southeastward, causing light ash falls in a number of population centers in the southeastern sector of the volcano (e.g., Pedara, Trecastagni, Mascalucia) to as far as Catania.
Analysis of samples of the ash revealed the very fine-grained nature of the deposit, with a clear predominance of lithic clasts and a negligible fraction of fresh juvenile material.
The explosive event of 25 August was accompanied by the collapse of a portion of the western rim of the BN-1 vent of the Bocca Nuova, rendering this area very unstable. During the following days, further explosions, internal collapse, and ash emissions occurred from the same vent. From 25 to 30 August there were 8 more significant events, though considerably smaller than the 25 August explosion: at 19:29 h on 25 August, 01:25 h on 26 August, 11:29 on 27 August, 11:15 and 16:18 h on 28 August, 07:40 and 09:31 h on 29 August, and 09:28 h on 30 August.
An aerial survey of the summit area was carried out between 08:30 and 09:30 h on 28 August, by staff members of the Catania section of the INGV (Luigi Lodato and Stefano Branca), carrying out thermal and visual observations of the summit craters. The survey was made with the aid of a helicopter provided by the forest fire counteraction squad of the Forest Service corps of the Sicily Region. The collapse of a significant portion of the western inner wall of the BN-1 pit was well evident; as a result of the collapse, debris was seen clogging the bottom of the vent, and also the nearby BN-2 pit was observed to be obstructed.
Observations made at the other summit craters are summarized as follows:
- The bottom of the Voragine was obstructed by rock detritus and showed only weak degassing from fumaroles lining the inner walls of the crater;
- The Northeast Crater showed degassing activity from the open pit on its floor;
- The Southeast Crater and the pit crater on the lower eastern flank of its cone were obstructed and showed weak degassing from fumaroles near the crater rims and on the upper slope of the Southeast Crater cone.
Thermal imaging confirmed the absence of thermal anomalies within the summit craters except for the Northeast Crater, which has an open pit on its bottom. The most significant thermal anomaly (~400° C) was found at a system of fumaroles in the inner wall of the pit crater on the eastern flank of the Southeast Crater cone.
STROMBOLI
Stromboli volcano is in a state of persistent eruptive activity, normally with explosions of medium to low intensity occurring from a number of vents located within the summit crater. During the month of August 2010, the activity continued at a level slightly lower than during the previous months, and showed the typical fluctuations characterizing the activity of Stromboli.
VULCANO
Vulcano volcano is currently in a state of quiescence. The M 4.5 earthquake of 16 August, whose epicenter lay at a short distance to the east of Vulcano, was not accompanied or followed by any significant variation in the monitored parameters (temperature and geochemistry of the crater fumaroles and other geothermal areas). Fumarole temperatures measured on the crater rim remained stable. No anomalies were observed in the geochemical parameters of the peripheral areas (soils in the Vulcano Porto areas and thermal aquifers).