Etna Volcano

Mount Etna towers 3340m over the city of Catania on the large Mediterranean Island of Sicily. The volcano has been frequently active in recent times and shows a combination of mild explosive activity, sometimes producing sustained ash columns, together with frequent A'a type lava flows which may reach runouts of several km. Spectacular paroxysmic lava fountaining events have been frequently observed at the summit craters in recent years. The summit complex consists of a main structure with two craters (Voragine and Bocca Nuova), a NE crater and the large SE crater which may become the highest point on Etna in years to come. All of these craters have been active in recent times. Lava flows from Etna in historical times have been frequently emitted from fissures low on the flanks of the volcano and the landscape on the flanks has many parasitic cones built up during this type of activity. The following text attempts to summarize the history of Etna in prehistoric and historic times including the most significant and recent eruptions.

Ash cloud from November 2002 eruption of Etna passing over the city of Catania. The city is frequently affected by ash which can lead to closure of the airport.	Earthquake damage caused by tremors accompanying the Nov.2002 eruption. Etna eruptions are frequently accompanied by minor earthquakes.

Summit region of Etna on evening of 24. Nov. 2006. Lava flows emanating from flank of the SE crater are visible.	Lava flow transporting rolling rock. Top of Valle del Bove, November 2006.

Over 500000 years ago, submarine basalt lavas layed the foundation of present day Mount Etna volcano. Thereafter, modest effusive structures were emplaced, which are now buried in the NE flaks of the volcano. The summit of the largest of these, Monte Callana (1325m) is still visible near Zafferana. About 80000 years ago, activity became increasingly explosive and the Trifoglietto stratovolcano was gradually built up. Little is visible of this structure today, although its remains make up much of the volume of the eastern flank of Etna. The Valle del Bove depression is the last visible remnant of the activity of Trifoglietto and signifies the location of its eruptive centers. Trifoglieto consisted of a number of highly eruptive centers which erupted huge amounts of scoriae, lapilli and ash during large eruptions which dwarfed the size of present-day eruptions at the volcano. The rapid emptying of the magma chambers resulted in numerous caldera-forming collapse events. The Valle del Bove is the result of a number off coalescing collapses.

It seems that between 65000 and 35000 years ago, activity was reduced at Etna. The center of present Mongibello volcano (today generally referred to as Etna) has since grown up on the SW flank of Trifoglietto, eventually covering most of the former structure. Two eruptive phases of Mongibello are distinguished. The "Antique" phase (35000-8000 years ago) was mostly explosive like Trifoglietto. The "Recent" phase (8000-0 years ago) has seen the establishment of more effusive activity and has led to the build-up of the present day structure including all of its summit craters.

Historical records at Etna date back many centuries. All historical eruptions were essentially effusive. Their impact on the local population depended primarily on the size and path of the emitted lava flows. In the past 8000 years, lava flows have covered the whole area in a radius of 15km from the summit. In many directions, these lavas coat the landscape to a distance of 20km and more. Much of these lavas erupted from fissures in the flanks rather than the summit area. The most notable historic eruptions are those that affected inhabited areas, in particular the city of Catania which is located on the coast 25km SE of the summit craters. Lava from an eruptive fissure 6km above the city inundated the northern parts of it in 1381 and reached the sea. In 1669, a vent opened at 850m altitude and erupted 1 cubic km of lava in 122 days. The flows reached a length of 15km, covered an area of 37.5 square km and entered the center of Catania. Eruptions from fissures low on the flanks often produce large amounts of lava since they can be fed from the conduit even when the level of magma therein has dropped significantly.

Lava flow fed from SE crater emerging at base of Hornito, top of Valle del Bove, November 2006.	Lava flow fed from SE crater emerging at base of Hornito, top of Valle del Bove, November 2006.

Since then , the largest eruption volume was in 1991-1993, when 0.3 cubic km of lava were emitted over a 473 period, starting on 14 December, from several vents along a huge fissure that extended from the base of the SE crater at 3000m to locations just over 2000m at the top of Valle del Bove. Up to 300m high lava fountains and strombolean and phreatomamatic explosions were observed in the first das of the eruption, after which activity settled into an effusive pattern at vents near the lowest part of the fissure. Lava flows rapidly entered the Valle del Bove, and by December had covered a distance of 7km to within 2km of the town of Zafferana. In order to save the town, attempts were made to stop the flows by building trenches and earth walls, the main trench was overflown on April 7 1992 and lava proceeded to within 1 km of Zafferana on 14 and 20 April. Explosive were deployed to try and disrupt the lava tunnels which had formed in the Vale del Bove and were feeding the lower parts of the flow. Further attempts were made by throwing concrete blocks into the lava tunnels to divert the lava out of them. These attempts were however only partially successful, slowing the flows for several days. After an initial attempt at rechanneling lava into an artificial channel brought some success, a new attempt was made. A large channel was excavated next to the main tube. After the channel had been completed, only a thin wall separated the tube from the channel. This was blown away on the 27th of May allowing a proportion of the lava to drain into the new channel. In the following days, complete diversion was achieved by blocking the natural tunnel just downstream of the channel using concrete slabs that were slid into it. This diversion was the first effective measure and together with reduced effusion rates by the end of June meant that the town of Zaferrana was saved. The eruption continued to send lava into the Valle del Bove from various vents along the fissure until ceasing on March 30, 1993.

Activity at the summit craters started again in July 1995 and spectacular ash eruptions, strombolian activity, lava flows and even intense lava fountaining episodes could be observed. Indeed in July 1997, all craters had become active in the summit region. On 4 September 1999, an unprecedented 1500m high lava fountain was observed from the Voragine (Main summit crater) and 5 Million cubic meters of material were deposited downwind. 5 cm long scoriae fell on the beach near Riposto and Giarre received a several cm thick layer of deposits. Accumulated hot pyroclasts on the S flank caused a debris avalanche to a length of 500m. Activity at the adjacent Bocca Nuova crater was elevated after 5 October 1999. On the 25th of October, an endogenous dome was formed at the S flank of the Bocca Nuova (the rim of which had already been covered with accumulating pyroclasts and breached by lava flows). Rockfalls forming from this dome had the appearance of classic pyroclastic flows reached up to 600m runout distances over a period of 40 minutes (the period during which dome growth could be observed). It is thought that magma rising up along the old crater wall pushed recently deposited and still hot pyroclastics, together with part of the crater wall upwards and outwards, leading to this short-lived dome-building event which is the first of its kind to be observed at a basaltic volcano (Behncke et al., 2003 (J. Volc. and Geotherm. Res. 124:115-128)). Up to 20 million cubic meters were erupted between 17 October and 3 November at the Bocca Nuova.

Early 2000 provided for repeated spectacular paroxysmal lava fountaining episodes and lava flows at the SE crater. In March, these eventually led to the partial destruction of the Torre del Filosofo mountain hut. Fountain heights of 500-600m, pulsing to over 800m were reported.

The eruptive period in July and August 2001 is interesting since several new vents opened and threatened the touristic facilities at Rifugio Sapienza. The eruption was preceeded by 14 paraxysmic lava fountaining episodes at the SE crater in the period from 17 June to 13 July. On July 17, a strong eruption at the SE crater was followed by the opening of an eruptive fissure at 3000m near its base. Later in the day, further vents opened at an elevation of 2800 and 2700m along a SSW line. Early on 18 July a vent opened at 2100m near the Sapienza Refuge, 200m uphill from Mt Silvestri crater. Minor lava fountaining ocurred and a lava flow crossed the road between the Silvestri carter and the Rifugio, proceeding 6km down the mountain in the following week. On July 19, a new cone (Montagnola II or Piano del Lago) was rapidly built 200m uphill from the 2600m Montagnola crater overlooking the upper cable car station. This cone erupted in a violent phreatomagmatic and later magmatic fashion, producing huge amounts of ash causing disruption to the city of Catania. Flows from vents near the base of this cone threatened the cablecar facilities and Rifugio (which was protected using an earth wall). On 28 July, powerful explosions threw car-sized projectiles to a distance of 500m from the vent. The upper cable car station was seriously damaged by these events, finally being set alight by a lava flow on 30 July. Eruptive activity diminished in August and ceased by the 10th of that month. A total of over 30 million cubic meters of material was erupted.

The next major eruption occurred starting on 27 October 2002. Eruptive fissures opened on both the N and S flanks resulting in lava fountaining and flows, accompanied by intense seismic activity which severely damaged buildings at Piano Provenzano (Note: a large Earthquake on 29 Oct. also damaged hundreds of homes in Sta Verenina). Lava flows from vents along the N fissure (at an altitude of 2500-1800m) rapidly spread over the Piano Provenzano tourist facilities, completing their destruction, and proceeded into the forests below in the direction of Linguaglossa, eventually stopping days later 5km from the vents. The N vents became inactive by November 3rd. The S fissure produced two large cinder cones (eventually reaching heights of about 200m each) at around 2700 and 2750m elevation. Activity at these initially involved fire fountaining with an associated large ash plume, together with lava flows of up to 2km. These flows stopped by 3 November but fountaining continued. On 9-10 December, vents at the base of the 2750m cone emitted lava flows which crossed the road by Rifugio Sapienza on December 17. 32 people wer injured by an explosion when a tank exploded inj a building that had been inundated by lava nearby. The Rifugio however survived once again, although the cable car facilities were again destroyed. Further shorter flows and strombolian activity at the new vents continued until 28 January 2003, when the eruption finally stopped. An estimated 70 million cubic meters of material was erupted, the majority of which (unusually) being pyroclasts.

Activity including paroxysms and lava flows have also occurred since 2003 but not reaching the same intensity or level of impact.

On May 13th 2008, the beginning of what appears to be a major fissure eruption of Etna has been reported. No details are available yet (13.05.08)

Ash eruptions from new vent, November 2002.	Ash eruptions from new vent, November 2002.	Ash eruptions from vent on flank of SE crater, November 2006.

Access to eruptions of Etna largely depends on the decisions of the local authorities restricting access. During the first weeks of the 2002-2003 eruption, roadblocks were set up near Nicolosi and Linguaglossa, severely restricting access. During the minor eruptions in Autumn 2006, access was regulated on an daily, sometimes hourly basis, and it was possible to get close to the lava flows entering the Valle del Bove. Lightning has caused more casualties on Etna than volcanic activity in recent times, and visitors should keep a good eye on the weather since there is little protection to be found in the summit region. The summit region is most easily approached using the cable-car from Rifugio Sapienza which takes one to an elevation of over 2600m, from where buses may take one up to an altitude of nearly 2900m. The Rifugio has a large parking lot for day tourists and comfortable accomodation is available at the Hotel Corsaro nearby.

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