Activity of the Sicilian volcanoes during November 2010

ETNA

During the month of November 2010, Etna has continued to show clear signs of unrest. In particular, there has been a significant increase of the activity of the Northeast Crater (NEC), which for many months had been characterized by deep explosions. Frequent emissions of vapor mixed with ash, at intervals of 1-2 minutes, were observed during a summit visit by INGV-CT staff on 12 November. On the morning of 14 November there was an augmentation in the frequency and volume of ash emissions from the NEC, generating plumes that rose a few hundred meters before being carried by the wind and forming a long trail, first toward southwest (14 November), then to northeast (during the night between 14 and 15 November), and finally toward east (15 November). These emissions occurred in an intermittent manner, alternating with emissions of white gas and vapor.

A visit to the summit craters was carried out by INGV-Catania staff on 15 November 2010, to make direct observations of the NEC activity and of the character of the ash deposits in the surrounding areas. Near the NEC cone, particularly to the south, in the northern portion of the Voragine, a few millimeters of brown ash were present on the ground. On the rim of the NEC itself, the deposit was up to 1 cm thick, especially on the eastern side, and of dark gray color. During the stay on the NEC rim, the ash emissions were rather modest, and accompanied by nearly continuous deep rumblings, sometimes becoming louder.

Since more than a year, on the crater floor there had been an open degassing vent, which until the previous visit to the NEC in October had a diameter of about 25 m. On 15 November, this vent was seen to be much larger, with a diameter of at least 75 m. Ash emissions from this vent occurred at times in a passive manner, but at times became more vigorous. The inner walls of the crater were covered by reddish brown ash deposits. No coarse-grained material was observed, neither in the deposits, nor in the emissions.

A sample of ash taken from the rim of the NEC was analyzed in the Laboratory of Sedimentology and Optical Microscopy (INGV-CT), revealing that 80% of the clasts had dimensions between 0.25 and 1 mm. About two-thirds (67 %) of the ash was juvenile material, most of this being tachylite fragments (61 %). The lithic fraction constituted 19 % of the sample, whereas the remaining 14 % were crystals, prevalently plagioclase.

Ash emissions from the NEC ceased late on 15 November, and remained absent for the second half of the month, while rhythmic emissions of vapor continued. Seismic signals characterizing the deep explosive activity during the previous month occurred at intervals of a few minutes through the end of November.

There have possibly been further ash emissions from the western vent (BN-1) of the Bocca Nuova, caused both by collapse of the crater walls and by explosions. A few seismic signals were recorded, which showed similar characteristics to those accompanying ash emissions during the previous months, but poor weather conditions precluded observations of possible ash plumes. The most significant event of this type occurred early on 1 November.

Intense gas emission continued from the pit crater located on the low east flank of the Southeast Crater cone. The summit visits carried out by INGV-CT staff on 12 and 15 November revealed that the emission occurs essentially from an open vent located at the base of the western wall of the pit crater, occasionally producing roaring sounds audible to 1 km away. During the first half of November, the pit crater also emitted small quantities of reddish-brown ash, which was sampled and analyzed in the Laboratory of Sedimentology and Optical Microscopy (INGV-CT). The sample was observed to contain a minor fraction (11%) of juvenile material (2% sideromelane and 9% tachylite). Intense fumarolic activity continued also from an extensive area on the upper east 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 November 2010, the activity continued with significant fluctuations, and during the first few days of the month generated small intracrater lava flows.

After the intense activity of 17-24 October, which had produced a first intracrater lava flow from a vent (S1) in the southern crater area (S area) of the crater terrace, intense spattering and low lava fountaining occurred from the same vent S1 on the early afternoon of 30 October. This activity was followed by the emission of a new tiny lava flow, which from S1 descended southeastward to be swallowed by the nearby vent S2. Further episodes of spattering from S1 were observed on 2 and 5 November, the earlier of these producing another small lava flow into vent S2. After this, S1 showed little activity throughout the rest of the month. Activity continued at vent S2 and from a vent in the northern crater area (N area) of the crater terrace, with explosions of coarse-grained material often rising more than 100 m above the vents. During the month, the frequency of explosions from these vents varied from 1-2 events/h (N vent, during the first week of November) to 18-18 events/h (vent S2, on 28 November), with occasional peaks of 23 events/h.

VULCANO

Vulcano volcano is currently in a state of quiescence. During the month of November 2010, no anomalies were observed in the geochemical parameters of the peripheral areas (soils in the Vulcano Porto areas and thermal aquifers).