Activity of the Sicilian volcanoes during January 2011
ETNA
During the first half of January 2011, significant eruptive activity has resumed at Mount Etna. The main event was the paroxysm at the Southeast Crater during the night of 12-13 January, after which the activity of the volcano has returned to rather low levels.
From the end of December 2010, weak eruptive activity has been observed within the pit crater located on the lower east flank of the Southeast Crater cone. Between 16.00 and 16.05 GMT on 23 December, during a sharp increase in the volcanic tremor amplitude, the visible monitoring camera of Schiena dell’Asino briefly recorded an intense glow in the location of the pit crater; inclement weather conditions precluded further observation. During the following 10 days, during brief intervals of clear views, intermittent weak glows and small incandescent emissions were observed at the pit crater, in particular during the night of 29-30 December.
On the late afternoon of 2 January 2011, an intense glow appeared at the pit crater, which during the following hours gradually evolved into a vivid, though modest, Strombolian activity. This activity was pulsating and increased in frequency, at the same time as there was an increase in the volcanic tremor amplitude and in the infrasonic activity recorded by the INGV-Catania monitoring networs. The peak was reached about midnight, and during the forenoon of 3 January, all recorded signals returned to background levels. For several hours, the eruptive activity consisted of Strombolian explosions that occurred at a rhythm of about 1-3 per minute, and launched bombs and scoriae up to a few tens of meters above the rim of the pit. Only rarely did incandescent bombs fall beyond the rim of the pit, mostly on the southern and eastern sides. There was no lava outflow, and no appreciable amounts of volcanic ash were produced.
During the following days, small emissions of incandescent material (probably mostly hot gas with minor to zero amounts of solid material) continued intermittently, producing weak and fluctuating glow at the active vent at night. After 6 January these phenomena diminished somewhat, but on the morning of 11 January, Etnean mountain guides observed small Strombolian explosions on the bottom of the pit crater. Durning the night of 11-12 January, the glow produced by this activity became well visible and the volcanic tremor amplitude started to increase slowly. This increase both of the volcanic tremor amplitude, and of the intensity of the Strombolian activity, continued throughout the day of 12 January; by late afternoon vigorous Strombolian explosions launched bombs and scoriae up to 100 m high, and pyroclastics frequently fell outside the rims of the pit.
At 20:10 GMT, a first small overflow of lava occurred on the low east rim of the pit, producing a flow only a few tens of meters long; this was followed at 20.18 by a second overflow following the same path and reaching the same distance. A third surge of lava at 20.26 initially advanced slowly on top of its predecessors, before due to an increase in the effusion rate it gained momentum, reached the western rim of the Valle del Bove, and started a slow descent down the steep western face of this depression shortly 21:00. As recorded by the Milo visible light monitoring camera, this flow stopped around 21.30 a few hundred meters below the Valle del Bove rim. In the same interval, the Strombolian activity within the pit crater rapidly augmented in intensity.
Between 21.50 and 21.55, the Strombolian activity rapidly passed into sustained lava fountaining to about 300-500 m height, and an eruption column rose at least 4000 m above the summit of Etna. This was accompanied by a sharp rise in the effusion rate, generating a new surge of lava, which overrode the previous flow and in a few minutes advanced beyond its stagnating front. During its descent on the steep western face of the Valle del Bove, the lava encountered patches of snow, which led to violent explosive interaction and the generation of small ash clouds. A small rheomorphic lava flow was formed on the northern side of the pit crater. At 21:58, the main lava flow had bifurcated into a main branch, which rapidly pursued its descent toward the bottom of the Valle del Bove, a minor branch further to the north, and several small lobes that advanced further south.
After 23:00, the height of the lava fountain showed a rapid diminution, and the fountaining became pulsating, with jets rising both vertically and obliquely into various directions, leading to heavy fallout of fluid spatter onto the rims of the crater. At 23:25, a single, narrow jet of fluid lava rose no more than 100 high; this jet was strongly inclined toward south, generating a small rheomorphic flow below the south rim of the pit. Simultaneously, feeding of the lava flows toward the Valle del Bove ceased; the main flow had in the meantime reached the bottom of the Valle to the east of Monti Centenari, stagnating at a distance of about 4.3 km from the eruptive vent. The incandescent jet, which for the last moments was only a few tens of meters high, faded away at 23:53. During the following hours, a few isolated explosions and ash emissions occurred; the strongest explosions occurred at 00:25 and 14:31 on 13 January.
The 12-13 January eruptive episode generated significant fallout of lapilli and ash in a sector extending south-southeast from Etna, affecting areas to as far as the south coast of Sicily. Near the eruptive vent, a thick armor of agglutinate was deposited, especially on the southern (downwind side). The composition of volcanic glass in scoriae of the paroxysm was found to be more primitive than that of the 2-3 January products, which essentially fall into the same compositional field as the minor amounts of fresh magmatic glass produced by the 8 April 2010 Southeast Crater and 22 December 2010 Bocca Nuova explosions.
Details of the 12-13 January pyroclastic fall deposit (in Italian)
After 13 January, no eruptive activity has occurred at the pit crater.
During the entire month of January, deep-seated explosions continued to occur within the conduit of the Northeast Crater. On windstill days, these explosions produced small puffs of vapor, and, occasionally, gas rings. Seismic signals characterizing the deep explosive activity as during the previous months occurred at intervals of a few minutes.
The Voragine and the Bocca Nuova remained quiescent during January 2011. During a helicopter overflight on 19 January, however, it was seen that collapse and subsidence on the western side of the Bocca Nuova had become more accentuated, and possibly extended also to the Voragine.
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 January 2011, the activity continued with strong fluctuations, culminating in four episodes of vigorous spattering and low lava fountaining, and emission of small intracrater lava flows. Previous episodes of increased activity, during December 2010, had occurred during the night of 11-12 December, with the emission of a small lava flow onto the upper south portion of the Sciara del Fuoco, and on 19 December, when a sequence of powerful explosions took place.
During all of January 2011, two vents in the northern portion of the crater terrace, N1 and N2, produced jets of bombs and scoriae varying from 80 to less than 150 m in height, and a mean frequency of 1-5 explosions/h.
In the southern portion of the crater terrace, various vents in shifting locations were active; initially only one large vent (S1) in the center of the southern crater area was erupting, but in the second half of the month it had transformed into three smaller vents. Explosions from this vent cluster occurred at a rhythm of 1-11 events/h, with maximum heights of the pyroclastic jets ranging between 120 and 200 m.
Vent S2, at the top of a small cone sitting on the western rim of the southern crater area, had remained inactive after the episode of spattering and lava emission of 11-12 December, but started to produce vigorous spattering at 18.46 GMT on 21 January. This new episode, which lasted until 21.00 on the same day, was characterized by the quasi-continuous emission of incandescent material, which upon falling back on the ground formed an agglutinate that slowly started to flow down the flanks of the conelet toward the deeper portions of the southern crater area. A similar episode of vigorous spattering occurred between 10.00 and 13.30 on 23 January, which culminated around 11.00 with virtually continuous fountaining to little more than 10 m height above the vent. Again, falling spatter formed an agglutinate that flowed from the conelet to the deeper portions of the southern crater area.
A third episode of intense spattering and low fountaining occurred during the morning of 25 January, reaching peak levels between 07.50 and 09.30. During this episode, there was no lava (or agglutinate) flow.
The fourth and most significant episode started about 19.30 GMT on 26 January, with vigorous spattering from vent S2, which around 20.00 increased to continuous lava fountaining to a height of a few tens of meters above the vent. The conelet of S2 rapidly was covered with fluid spatter, forming a small lava flow that expanded northeastward, and after covering the central portion of the crater terrace buried the lava flow of 18-19 October 2010. A second lava flow was emitted between 23.00 and midnight, taking a more southerly parcourse, and covering nearly completely the area of the S1 vents. Shortly before 05.00 on 27 January, after a few hours of relative calm, spattering resumed at S2, generating a third small lava flow around 05.25, which travelled on top of the first flow but stopped at a shorter distance from the vent.
During the last few days of the month, the explosive activity of Stromboli continued at relatively low levels.
VULCANO
Vulcano is currently in a state of quiescence. During the month of January 2011, temperatures measured in fumaroles 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).