****************************** Summit eruption continues at Mount Etna Istituto Nazionale di Geofisica e Vulcanologia ? Sezione di Catania From: Boris Behncke (behncke@xxxxxxxxxx) and Sonia Calvari (calvari@xxxxxxxxxx) ****************************** (All times are in GMT) Episodic eruptive activity continued at the South-East Crater of Etna (SEC) until December 2006, involving a number of explosive and effusive vents on and around the SEC cone. Continuous lava effusion occurred from a vent at 2800 m elevation on the western headwall of the Valle del Bove, which had become active on 13 October. Explosive activity temporarily stopped on 7 December, but resumed four days later. The following is summarized from daily observations made by researchers of the INGV staff and their reports posted on the INGV-CT web site (www.ct.ingv.it). Updated reports of the activity (in Italian) are available at the page dedicated to the 2006 activity at http://www.ct.ingv.it/Etna2006/Default.htm. After two days of pause from the previous eruptive episode, the SEC produced its 16th eruptive episode on 24 November. Ash emissions mixed with Strombolian explosions started at 02:19, when the INGV-CT thermal monitoring camera located in Nicolosi (~15 km S of the SEC) began to record a significant anomaly at the SEC summit. Strombolian activity at 03:20 was accompanied by voluminous ash emission, which formed a plume that rose about 2000 m above the summit before being blown to SE. Two particularly powerful explosions occurred at 04:52 and 04:55, the second of which was followed by the extrusion of lava from a vent presumably located within the 16 November trench. Lava began to extrude from the 3050 m vent on the S flank of Bocca Nuova at around 05:35, forming a small flow on the W side of the lava flow field emplaced since 26 October. A second minor flow issued from another vent located about 80 m SE of the 3050 m vent. Vigorous ash emission from the summit of the SEC caused light ashfalls over populated areas between Zafferana and Acireale. A fracture opened at about 08:17 at the SSE base of the SEC cone, producing a violent explosion and a rock avalanche that descended at a speed of several tens of km/h toward the Valle del Bove, following the path of similar avalanches that had occurred on 16 November. Lava effusion continued from vents at the base of the cone, where mild spattering was observed. A second fracture formed upslope from the effusive vent at 2800 m elevation displaying spattering and lava emission. During the early afternoon a change in the wind direction drew the plume from its earlier SE-ward course toward Catania and adjacent areas, forcing the closure of the Fontanarossa International airport of Catania. The activity began to diminish and by 15:30 all explosive phenomena ceased, while lava continued to issue from two vents at the base of the SEC cone for several hours. Late in the afternoon, weak, sporadic Strombolian explosions occurred from a pit located on the E flank of the SEC cone, which had formed during the 23 October eruptive episode (hereafter named ?23 October pit?). On 25 November this vent produced pulsating ash emissions that continued intermittently for the next two days. On the early morning of 27 November, eruptive episode #17 occurred at the SEC. Eruptive activity started around 04:10, when the thermal monitoring camera at Nicolosi (~15 km S of the SEC) began to record a significant thermal anomaly at the crater, and an ash plume drifting W. Visual observations were hampered by inclement weather. Around 07:30, imagery from the thermal monitoring camera at Nicolosi allowed to recognize lava emission on the W side of the SEC cone, possibly from the vent at 3180 m elevation in the saddle between the SEC and the Bocca Nuova. Approximately 45 minutes later, lava emission became also evident at the SE base of the cone. No further visual observations were available after 08:45, but the volcanic tremor amplitude remained high until the afternoon, when a sharp drop indicated the end of this eruptive episode. Bad weather persisted until early on 29 November, when ash emissions from the 23 October pit on the E flank of the SEC cone became again visible. These became more intense after 05:45, and the volcanic tremor amplitude began to increase rapidly during the later forenoon. Intermittent, weak Strombolian activity from the 23 October pit was visible after nightfall; this became notably stronger shortly after 01:00 on 30 November and reached its highest intensity around 01:30, after which there was a notable decrease. Ash emissions occurred from the same pit at dawn and again from 12:40 onward, producing low ash plumes. Eruptive episode #18 came on 30 November and significantly differed from its predecessors. At around 16:00 on that day, lava fountains began to rise from the 2800 m vent. Two hours later there was a significant increase in the level of activity at the 23 October pit, which emitted a dense plume of ash, and Strombolian explosions reached up to 150 m above the vent. At 20:45, a fissure opened at the base of the SEC cone, at ~3100 m elevation, producing vigorous spattering several tens of meters high and a short lava flow that extended in the direction of the 2800 m vent. After about 10 minutes the activity of this new fissure diminished, but lava emission continued at a decreasing rate for about one hour. The 23 October pit remained vigorously active for the next 5 hours, producing incandescent jets and a dense tephra plume. The new fissure at 3100 m elevation revived around 01:15 on 1 December, with vigorous spattering and a new surge of lava directed toward the 2800 m vent. Activity at the 23 October pit showed a strong increase at the same time. Like on the evening before, the new fissure at 3100 m elevation remained active only for a short time; lava emission ceased by 02:00 on 1 December. The 2800 m vent produced the largest lava flows during the entire period of activity, extending to ~1500 m elevation on the Valle del Bove floor, at approximately 4.7 km distance from their source. Between 1 and 3 December, the 23 October pit remained active with nearly continuous emissions of ash interspersed with Strombolian activity accompanied by low fountaining and lava emission from the 3100 m fissure. Lava flows from that fissure were generally short and did not extend far beyond the 2800 m vent. The last observed activity at this vent occurred during the foreneoon of 3 December. Ash emissions from the 23 October pit continued for another few days but became progressively weaker; likewise the lava emission at the 2800 m vent diminished gradually. The episode # 19 of weak Strombolian activity and ash emission occurred on the afternoon of 6 December, as evidenced by increased volcanic tremor. After that the tremor amplitude dropped rapidly to very low levels, and eruptive activity at the SEC ceased late on 6 December, whereas lava continued to be emitted at a low rate from the 2800 m vent. On the morning of 8 December, no eruptive activity was visible at any of the numerous vents that had participated in the activity of the previous weeks. Following several days of very low level, volcanic tremor amplitude began to increase again late on 10 December. Eruptive activity resumed around 03:30 on 11 December giving rise to episode # 20, occurred from the 23 October pit on the SEC, with Strombolian explosions that were recorded by the monitoring cameras of the INGV-Catania. Simultaneously, lava emission started from the area of the 2800 m vent, forming a flow that slowly descended toward the Valle del Bove. Calculation of the areas covered with lava during the 2006 summit eruptions (July-December) yields a rough estimation of the erupted volumes. The 14-24 July activity produced a lava field covering 0.65 km2, with a volume of ~3 x 106 m3. The lavas emitted from the 3050 m vent covered about 1.1 km2, and their volume amounts to ~3 x106 m3. The largest lava field was produced by the 2800 m vent, covering 1.35 km2, with a volume of ~7 x 106 m3. The volumes of lavas produced during overflows from the SEC summit vent and from fissures on its flanks is in the range of 1 x 106 m3. The total volume of lava produced during the 5 months of summit activity in 2006 thus amounts to ~ 14 x 106 m3. Dr. Sonia Calvari Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania Piazza Roma 2 95123 Catania (Italy) Tel. +39 095 7165800 direct: +39 095 7165862 Fax: +39 095 435801 url: www.ct.ingv.it ============================================================== To unsubscribe from the volcano list, send the message: signoff volcano to: listserv@xxxxxxx, or write to: volcano-request@xxxxxxxx To contribute to the volcano list, send your message to: volcano@xxxxxxxx Please do not send attachments. ==============================================================
