Activity of the Sicilian volcanoes during February 2011

ETNA

During February 2011, the eruptive period of Etna initiated during the previous month continued with a new paroxysm from the Southeast Crater (SEC). This episode took place on 18 February, 36 days after the paroxysm of 12-13 January, from the pit crater on the lower east flank of the SEC cone. Being energetically less significant, this episode was in its main outlines similar to that of its predecessor, with violent Strombolian activity and pulsating lava fountains as well as the emission of a lava flow about 3.3 km long, which covered parts of the 12-13 lava flow. Ash emission was less intense and of minor volume compared to the January event.

For the first half of the month, Etna remained relatively calm, with strong degassing from the Northeast Crater (NEC) and from the Bocca Nuova, and the usual deep-seated explosions within the conduit of the NEC. During a field visit to the summit area by INGV-Catania staff on 10 February, detonations were heard that probably resulted from the explosive activity deep within the NEC conduit. On the evening of 16 February, a rapid increase of the volcanic tremor amplitude culminated in a sequence of explosive events possibly at the NEC, but cloud cover prevented direct visual and thermal recording of any eruptive phenomena.

During the first half of the month, the SEC showed weak degassing from fumaroles on its main crater rim. Gas emission from the pit crater was either very limited or completely absent except for a very small and short-lived emission of ash on 7 February at 11:17 GMT.

At 03:30 on 18 February, a strong increase in the volcanic tremor amplitude was accompanied by vigorous explosive activity, which was recorded by the thermal monitoring camera at the Montagnola (EMOT). For many hours, visibility was hampered by extremely poor weather, but analysis of the images recorded by the monitoring cameras revealed that strong, pulsating emission of hot gas from the pit crater started at 01:15 on 18 February, followed at 01:48 by sporadic, deep-seated explosions on the bottom of the crater. Between 03:12 and 04:30 explosive activity increased and were periodically well visible in the images of the thermal camera of the Montagnola.

Weather conditions temporarily improved around 12:34, revealing that a lava flow had been emitted from the eruptive vent into the direction of the Valle del Bove; this flow was partly visible in the images recorded by the Milo monitoring camera. The thermal camera at the Montagnola recorded ongoing eruptive activity with pulsating lava fountain, which rapidly decreased in intensity until all activity ceased at 13:17.

The lava flow produced by this episode followed the same path of the 12-13 lava flow, but formed a single main flow lobe, which came to a halt at 1800 m elevation to the north of Monte Centenari, at a distance of about 3.3 km from the vent.

After 18 February no eruptive activity was observed at the pit crater; deep-seated explosive activity continued at the NEC, producing a pulsating, “puffing” gas plume in particular on windstill days.

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 February 2011, the activity continued with fluctuations, showing an increase during the second half of the month.

In the southern portion of the crater area, vent S1, produced weak to moderately strong explosions of fine-grained material mixed with coarse-grained pyroclastics during the first three weeks of the month. Sometimes the jets reached 120 m height above the crater terrace. The frequency of explosions in this area during this period was 1-6 events/h. During the last week of the month, S1 produced sporadic, relatively weak explosions (less than 80 m high) of pressurized gas mixed with coarse-grained pyroclastics. Another vent, S2, produced mainly fine-grained material mixed with coarse-grained pyroclastics until the morning of 26 February, and from the afternoon of that day on, mainly coarse-grained material sometimes mixed with finer clasts. The intensity of these explosions was low to moderate, with jets sometimes reaching 120 m height above the crater terrace. The mean frequency of explosions during the last week of February was 6-11 events/h.

During the first half of the month, vent N1 in the northern crater area produced jets of coarse-grained pyroclastics (lapilli and bombs) of moderate intensity (less than 150 m high above the crater terrace). From 16 February on, eruptive activity at N1 increased in intensity, producing explosions that dispersed pyroclastics over a wider area, but maintaining the same mean frequency as during the previous days. From 16:00 on 17 February, explosions – though slightly weaker than those on the previous day – started producing larger volumes of coarse-grained material, which covered a wide area on the upper Sciara del Fuoco slope. Accumulation of this material, which remained hot for prolonged periods – often until the next explosion – created a persistent thermal anomaly on various sectors on the slope. These more voluminous explosions were again observed on the afternoon of 19 February and continued intermittently through the end of the month.

Vent N2, located a bit further south, started an intermittent, weak spattering activity on 17 February, which extended over prolonged periods on 20 and 21 February and continued in a similar manner through the end of the month. The mean frequency of explosions in the northern area was 1-4 events per hour.

VULCANO

Vulcano is currently in a state of quiescence. During the month of February 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).