Eruptions since 1971

After nearly twenty years without any major flank eruption (the minor effusions from vents on the eastern flank in 1956, 1964 and 1968 are generally considered as strongly related to the activity of the summit craters), a series of flank eruptions following each other in rapid succession started in early April 1971.
During the following 22 years there were no less than 13 true flank eruptions and two events that can be considered a "hybrid" between flank eruptions and sub-terminal activity closely related to the summit craters. Nine of the flank eruptions (1971, three eruptions in 1978, 1979, December 1985, 1986-1987, 1989 and 1991-1993) occurred within or near the Valle del Bove and involved, in some manner, the Southeast Crater, two others (1983, March-July 1985) occurred on the south flank but were related to SE Crater as well while only two eruptions occurred away from these particularly active zones, on the NNW flank in 1981, and on the W flank in 1974. The "hybrid" eruptions occurred in 1975-1976 on the northern flank, close to the NE Crater to which they were directly related.
A new eruptive cycle began after the end of the volumetrically large 1991-1993 eruption, with activity confined to the summit area until July 2001. A new flank eruption occurred in 2001, which probably was the first in a new series of flank eruptions similar to that of 1971-1993. The second eruption of this series began only one year and three months later, in October 2002.
Below brief descriptions are given of all important eruptive events since 1971. They include links to a series of pages dealing with the individual eruptions during this period, and which contain maps, photos, and brief descriptions of the events as well as - where available - references.

1971 SUMMIT AND E FLANK ERUPTION
This eruption consisted of two distinct phases.
- First phase: 5 April - 7 May. Activity occurred from four radial fissures at the southeastern base of the summit cone.
Fissure 1 lay at 3000 m, fissure 2 at 2960 m, fissure 3 at 3020 m, and fissure 4 at 2880 m elevation.
Lava flowed southwards (across the Piano del Lago - the relatively gently sloping area north of Montagnola) and ESE (into Valle del Bove). During this phase the old Etna Observatory, built in the late 19th century, was buried under lava. The top station of the cable car and numerous poles of the cable car were also destroyed. Several scoria cones or cone complexes grew at the vent.
- Second phase: 7 May - 12 June. On 7-8 May, seven fissures opened across the western rim of Valle del Bove along an ENE-trending fracture system propagating downslope. The six major fissures were located at elevations of 2680 m, 2580 m, 2450 m, 2300 m, 1840 m and 1800 m. Two fissures located at Contrada Serracozzo (near the Rifugio Citelli, outside the Valle del Bove) produced the most destructive flows that threatened the villages of Fornazzo and Sant'Alfio, and caused widespread destruction (loss of 2.5 square kilometers of agricultural land). During this phase, on 14 May, a new pit formed at the southeastern base of the summit cone: this pit was later to become the SE Crater (or SE Cone). During the second phase of the 1971 eruption it served as a degassing vent while degassed lava issued further downslope.
Total area covered by lava flow: 7.5 square kilometers, maximum flow length: 4 km (first phase - down to 2175 m); 7 km (second phase - down to 600 m elevation). Volume: 75 million m³ of lava; 3 million m³ of pyroclastics. Mean effusion rate: 13 m³ per second.

Maps and photos of the 1971 eruption

1971-1973 SUMMIT ACTIVITY
After the 1971 eruption, magma rapidly rose again within the conduit of the Voragine to 200 m below the crater rim, and mild intracrater activity occurred throughout 1972. In 1973 Strombolian activity occurred on the floors of the Voragine and of the Bocca Nuova, causing rapid filling of these craters, and by mid-August 1973, the level of lava fill was only 50 m below the rim of the Bocca Nuova. Vigorous eruptive activity occurred at the Voragine during the first days of November, culminating in an episode of lava fountaining, accompanied by phreatomagmatic explosions, on 6 November. Thereafter the activity decreased, and the magma column within the two craters subsided, leaving the Bocca Nuova several hundred meters deep, while the floor of the Voragine was about 70-80 m below the rim, with a collapse pit in its center. Deep-seated explosive activity continued through January 1974 and increased again towards the end of that month, just before the onset of the flank eruption (see next paragraph), when magma rose to within 30 m of the rim of the Voragine.

Maps and photos of the 1971-1973 activity

1974 W FLANK ERUPTION
This eruption consisted of two distinct phases.
- First phase: 30 January - 16 February. Activity occurred from one single crater at 1670 m elevation (6 km from the summit). Effusive activity was irregular and involved up to six distinct vents on the flanks of the cone, and there were also occasional overflows from the main vent. Volume of lava of the first phase: 2.4 million m³ (area covered 0.3 square kilometers); volume of pyroclastics: about 2 million m³. Mean effusion rate: 1.63 m³ per second.
- Second phase: 11-29 March. A new crater with a single vent opened about 200 m west of the first one at 1650 m elevation. Vigorous Strombolian activity built a horseshoe-shaped cone open to the W with lava flowing out through the breach. The lava flow extended about 1.3 km downslope to 1400 m elevation, covering an area of 0.2 square kilometers and with a volume of 2.1 million m³. Volume of pyroclastics: 1.1 million m³. Mean effusion rate: 1.34 m³ per second.
The two pyroclastic cones formed during the 1974 eruption were soon named Monte de Fiore I and Monte de Fiore II in honor of the famous Italian volcanologist of the first half of the 20th century.

Maps and photos of the 1974 eruption

1974-1978 NE CRATER ERUPTIONS
Long-lived eruption consisting of two distinct phases.
- First phase: 29 September 1974-January 1977. For the first five months, classical persistent activity occurred at the NE Crater, inactive since early 1971: mild Strombolian explosions accompanied by slow lava effusion. On 24 February 1975 lava effusion began from a vent about 1 km N of the NE Crater (2600 m elevation), while activity ceased at the NE Crater. After a short-lived return of the activity to that crater, new vents became active about 1.5 km N of the NE Crater, near Punta Lucia, on 29 November 1975, and lava effusion accompanied by mild Strombolian activity continued at these vents until the first days of 1977.
- Second phase: 16 July 1977-29 March 1978. During this period the NE Crater produced about 20 short-lived episodes of very violent (paroxysmal) eruptive activity, consisting of fire-fountaining and voluminous lava emission. Fountains jetted to heights of several hundred meters above the summit of the rapidly growing NE Crater cone, and lava flows extended several kilometers (max. 7 km) from the crater towards NE, NNE, N and NW. During January 1978 the NW side of the crater rim was breached, channelling all consecutive lavas into that direction.
The full volume of eruptive products of the period 1974-1978 ranges from 55 to 80 million m³ (mostly lavas; no estimate of the volume of pyroclastics is known). The mean effusion rate was about 1 m³ per second, but during the second eruptive phase (1977-1978) the eruptive activity was concentrated in very short, high-effusion rate episodes. The highest point of the NE Crater cone was at 3345 m elevation after the end of the activity, higher than the formerly highest point of the volcano, the 1964 cone S of the Voragine.

Maps and photos of the 1974-1978 eruptions

1978 SUMMIT AND E FLANK ERUPTIONS
Three summit/flank eruptions took place during 1978.
- First eruption: 29 April-5 June. Vigorous eruptive activity started at the 1971 collapse crater at the SE base of the main summit cone, which was soon to be named "SE Crater". During the following days eruptive fissures extended to the SE towards the Valle del Bove, at elevations of 2900 m, 2700 m and 2600 m, producing extensive lava flows. Lava volume: 23 million m³, mean effusion rate: 7.2 m³ per second.
- Second eruption: 23-30 August. The first stage of this eruption consisted of increasingly vigorous Strombolian and effusive activity at the SE Crater. A complex system of eruptive fissures extended from the SE Crater to the SE and NE during the last three days of the eruption, feeding various lava flows that reached the bottom of the Valle del Bove. Lava volume: 3 million m³, mean effusion rate: 5.8 m³ per second.
- Third eruption: 18-29 November. Similar to the August 1978 eruption, with gradually increasing activity at the SE Crater during the first week of the activity, followed by the establishment of a system of eruptive fissures to the E and SE of the SE Crater, with the main vents at 2600 m, 1800 m, 1700 m and 1650 m elevation. The main lava flow rapidly ran downslope along the S margin of the Valle del Bove and reached the Val Calanna, a few kilometers from the village of Zafferana. Lava volume: 5 million m³, mean effusion rate: 4.7 m³ per second.

Maps and photos of the 1978 eruptions

1979 SUMMIT AND E-NE FLANK ERUPTION
Eruptive activity started at the Voragine in late June and at the SE Crater in mid-July, intensifying gradually at both craters through the first days of August. On 3 August violent lava fountaining and ash emission started at the SE Crater, followed immediately by the reactivation of the main 1978 fissure (trending SE from the SE Crater), and emission of copious lava flows towards the Valle del Bove. Ash from the explosive activity fell on Catania, forcing the closure of the airport, and even on Siracusa, 80 km S of Etna. On 4 and 5 August new fissures opened in various locations in the NW sector of the Valle del Bove: below M. Simone, at 1800-1700 m elevation, on the W wall of the Valle del Bove, and in the Valle del Leone above M. Simone. The fissure at 1800-1700 m fed a voluminous flow which ran eastwards in the N part of the Valle del Bove, cascaded through the narrow valley of the Torrente Fontanelle and rapidly advanced towards the village of Fornazzo, cutting the Fornazzo-Rifugio Citelli road at the southern margin of the 1971 flow-field. The village, which was under serious threat for the third time in less than 30 years (after 1950-1951 and 1971) was evacuated; the flow stopped 50 m from the main road of Fornazzo, having destroyed only one isolated building. Renewed violently explosive activity occurred at the SE Crater on 5 August, again showering Catania, Siracusa and nearby villages with ash. More lava was poured from the Valle del Leone vent on 6 August, before later that day an eruptive fissure opened outside the Valle del Bove, in almost exact coincidence with the upper 1928 eruptive fissure. Fortunately, the effusion rate at this fissure was low (in contrast to that of fissures active earlier in the eruption), and a minor lava flow ran in the direction of the Rifugio Citelli, halting after two days immediately before reaching the road leading to the Rifugio. All activity was over by 9 August, thus ending one of the most dramatic and energetic eruptions of the past decades.
Lava volume: 7.5 million cubic meters, maximum flow length 6 km; the volume of pyroclastics is undetermined but may have been in the range of 1-2 million m³, similar to that of other recent paroxysmal eruptive episodes in the summit area. The mean effusion rate was 14.4 m³ per second, with peaks up to an order of magnitude higher.
As a tragic epilogue to the eruption, nine tourists were killed and more than 20 injured on 12 September 1979 by a sudden phreatic explosion from the Bocca Nuova; this event was in turn followed by a highly polemic controversy between various groups of volcanologists, and by strict access limitations to the summit area.

Maps and photos of the 1979 eruption

1980-1981 SUMMIT ERUPTIONS
Vigorous eruptive activity resumed in the Voragine on 14 April 1980, culminating two days later in a series of explosions, and rapid filling of the crater to within 25 m of its rim. Mild Strombolian activity at the SE Crater, punctuated by episodes of more intense activity, occurred between February and August 1980. On 1 September the activity shifted to the NE Crater, rapidly building up to a paroxysmal eruptive episode characterized by fire-fountaining and emission of lava flows. Early the next day the activity waned, but another, similar paroxysmal episode occurred on 6 September, and a third one took place on 26-27 September. The total volume of lava produced by the three episodes was 2-3 million m³.
The NE Crater became active again in late January 1981 with ash emissions, and an episode of paroxysmal activity occurred between 5 and 7 February, emitting about 2-3 million m³ of lava and raising the height of the top of the NE Crater cone to 3350 m elevation.

Maps and photos of the 1980-1981 activity

1981 NNW FLANK ERUPTION
Following hundreds of small premonitory earthquakes, a system of eruptive fissures began to open between 2625 and 2500 m on the N flank of Etna on 17 March 1981, producing lava fountains, phreatic explosions, and voluminous lava flows. The fissure system rapidly propagated downslope, assuming a NNW trend, and on the evening a large fissure segment at about 1800 m emitted a lava flow which travelled towards N at awesome speed (more than 1 km per hour). As this flow approached towards the village of Montelaguardia, about 3.5 km from Randazzo, more eruptive fissures opened at ever lower elevations through the morning of 18 March, emitting lava flows and building small pyroclastic cones. The village of Montelaguardia was evacuated, but the main lava flow passed half way between this village and Randazzo, destroying agricultural land, farm houses and villas before interrupting roads, the Circumetnea railway, the Statal railway, and power and telecommunication lines during the night of 17-18 March. By the late forenoon of 18 March, the front of the eruptive fissure system was at about 1400 m elevation, and lava from these new vents began to approach directly towards Randazzo; at this time the main lava flow reached the Alcantara valley at much reduced speed; it would later stop short of the river bed, having reached a length of 7.5 km.
On the afternoon, yet more eruptive fissures opened at yet lower elevation (1250-1150 m), producing minor lava flows which slowly advanced in the direction of Randazzo. While many residents voluntarily left their homes in that town, no evacuation was ordered, because the eruption had lost much of its early vigor. Strombolian activity in the lowermost part of the eruptive fissure system continued until 23 March, building a small pyroclastic cone, and minor amounts of lava were extruded, forming a sluggish flow that stopped 2 km S of Randazzo.
The total volume of lava emitted in the 1981 eruption was estimated at 18-30 million m³ (the lower figure is generally accepted), and about 1 million cubic meters of pyroclastics were deposited mainly in the form of spatter ramparts and hornitos or small scoria cones. Most of this material was produced during the first 2 days of the eruption, when peak effusion rates may have been as high as 200-300 m³ per second, an exceptionally high value for Etna. The mean effusion rate was between 34.7 and 55 m³ per second, according to the various volume estimates.

Maps and photos of the 1981 eruption

1981-1983 SUMMIT ACTIVITY
During the NNW flank eruption of March 1981 the Bocca Nuova emitted ash plumes near continuously, caused by collapse related to the withdrawal of magma in the central conduit system. Vigorous degassing, accompanied by occasional explosions, occurred throughout the year, and towards the end of the year, large portions of the Bocca Nuova rim collapsed, enlarging the pit towards SW and S.
In 1982 two significant events occurred: the explosive disruption of the lava-filled floor of the Voragine on 27 May (which fortunately occurred when no people were in the summit area), and a period of intense Strombolian activity in the Bocca Nuova during the summer, reaching its climax in early August. The activity waned during late-1982 and early-1983.

1983 S FLANK ERUPTION
After a series of small earthquakes, an eruptive fissure opened at 2450-2250 m elevation on the S flank, to the W of the Montagnola, on the morning of 28 March 1983, and lava began to spill down the steep slope towards the complex of tourist facilities around the Rifugio Sapienza. During the following days most of the buildings at the tourist complex were destroyed, including the "Ristorante Corsaro", the Hotel "Cantoniera" and the Hotel "La Quercia". A ski lift was damaged, but the cable car (rebuilt after destruction during the 1971 eruption) was left unharmed. A lava tongue surrounded the Rifugio Sapienza, before the eruptive fissure lengthened somewhat, feeding new lava flows that ran down the slope slightly more to the W; the Rifugio was saved. On 1 April two pits formed at about 2700 m elevation, from which mainly old fragmental material and gas were ejected. The lava field gradually extended downslope, interrupting the Nicolosi-Rifugio Sapienza road in many places, destroying forest and patches of agricultural land, and burying numerous isolated buildings. Differently from the 1981 eruption the effusion rate was low, resulting in the emplacement of a complex lava flow-field consisting of countless overlapping and adjacent flow lobes. Growth of the flow-field continued mainly through late-May; after this most lava lobes flowed on top of earlier lavas, and the eruption continued at a fluctuating rate until 6 August 1983.
The maximum flow length was about 7.5 km, with the farthest flow front stopping no less than 7 km from the nearest towns (at 1080 m), and the area covered by lava was about 6 square kilometers. The total volume of lava emitted was, according to various estimates, 80-100 million m³, while a neglegible amount of pyroclastics was produced. The mean effusion rate was - relative to the various volume estimates - 6.2 to 8.9 m³ per second. The flank eruption was accompanied by frequent collapse and explosions within the Bocca Nuova.
Various measures were applied to control or modify the advance of lava flows during the 1983 eruption. The blasting of the main feeder channel close to the eruptive fissure on 14 May resulted in the diversion of only a small portion of lava into an artificial channel, but lateral growth of the lava field near the Rifugio Sapienza and the Grande Albergo and the Etna Astronomical Observatory could be prevented by building lateral earth barriers. These protective measures were carried out in an atmosphere of harsh controversy between various groups of scientists, environmentalists, the local population and administration.

Maps and photos of the 1983 eruption

1984 SE CRATER ERUPTION
Long-lived summit eruption at the SE Crater, lasting from 29 April to 18 October 1984, a beautiful example of persistent activity with Strombolian explosions and relatively slow lava effusion. A new pyroclastic cone about 60 m high was built within the collapse depression formed at the crater during 1978-1979, and lava spilled into the Valle del Bove, extending up to 4 km from the vent. The cessation of the activity was followed by short-lived activity at the Voragine and the Bocca Nuova, and by a sequence of local but damaging earthquakes on the E flank which killed one person, injured several others and destroyed or damaged numerous buildings in the villages of Fleri and Zafferana.
Volume of lava of the 1984 eruption: 10-15 million m³, corresponding to a mean effusion rate of about 1 cubic meter per second. Area covered by new lava: 1.5 square kilometers, maximum flow length: 3 km.

Maps and photos of the 1984 eruption

1985 S FLANK ERUPTION
A similar eruption to that of 1983, occurring in the same general area, but smaller and less destructive. An episode of paroxysmal lava fountaining and flow emission at the SE Crater on 8 March 1985 was followed two days later by the opening of an eruptive fissure at 2600-2450 m elevation. Mild Strombolian activity built a row of hornitos immediately above the "Piccolo Rifugio" (a part of the eruptive fissure ran right across the building, and lava flowed out of its lower floor), and lava flowed to the S and SSW, burying the hornitos of 1983 and damaging the cable car. Most of the lavas then spread in an area adjacent to the W margin of the upper part of the 1983 lava flow-field, initially arousing fears for the safety of the "Grande Albergo" and the Astronomical Observatory, but the effusion rate was quite low and most lavas extruded after the first days of the eruption were emplaced on top of the earlier flows or adjacent to them, without extending far beyond the boundaries of the new lava flow-field. The eruption ended on 13 July 1985, having emitted 30 million m³ of lava at a mean effusion rate of about 2.7 m³ per second. Maximum flow length: 3 km (down to 1830 m above sea-level).

Maps and photos of the 1985 S flank eruption

1985 E FLANK ERUPTION
A strong local earthquake occurred along the Pernicana fault (N flank of Etna) on 25 December 1985, destroying the hotel "LeBetulle" at Piano Provenzana, killing one person and injuring several others. This was followed by the opening of an eruptive fissure on the W slope of the Valle del Bove (at about 2750 m elevation) from which lava fountains jetted tens of meters high, and a lava flow ran across the floor of the Valle. Following an initial vigorous phase, the activity decreased, and temporarily ended on 26 December, then resumed again on the 28th from a fissure located at a slightly lower elevation (about 2600 m) to end altogether on 31 December. The lava flow travelled about 3.5 km (down to about 1680 m); its volume was 1-2 million m³, and the mean effusion rate of the eruption was about 3-3.5 m³ per second.

Maps and photos of the 1985 E flank eruption

1986 NE CRATER ERUPTION
After about 5 years of almost complete quiet, the NE Crater became again active in July 1986 with mild Strombolian activity. In early September this activity gradually increased, and a small pyroclastic cone was built around the eruptive vent, while lava slowly issued from vents at its base, accumulating on the crater floor. On 14 September lava began to overflow the crater rim and advanced to the NW, cutting the dirt road leading to the summit area from Piano Provenzana. On 22-23 September the level of eruptive activity was particularly high, with continuous Strombolian explosions and lava outflow at the NE Crater, Strombolian activity at the floor of the Bocca Nuova, and mild explosive activity at the SE Crater. On the next morning the activity had ceased in all craters, and non-eruptive fractures had formed to the NE of the NE Crater, whose intracrater cone had collapsed. Later that day phreatomagmatic activity began at the NE Crater, gradually intensifying, and culminating in the late afternoon with one of the most violent paroxysms seen at Etna in many years. At the climax of the eruption, lava fountains jetted 1000-1500 m above the vent, and the summit area was showered with large bombs; an eruption column rose 10-13 km high. Dozens of volcanologists who worked on Etna escaped miraculously and unharmed. Ash fell to the SSE, reaching also Catania and forcing the closure of its airport.
The volume of pyroclastics ejected during the paroxysmal eruptive episode of 24 September 1986 was 1-3 million m³, while that of the lavas emitted during the days before the paroxysm was less than 1 million m³; the area covered by new lava was 0.02 square kilometers, with a maximum flow length of 1.3 km (down to about 2900 m). The NE Crater lost more than 10 m in height and displayed little eruptive activity for the following 9 years.

1986-1987 ENE FLANK ERUPTION
Only five weeks after the NE Crater paroxysm, on 30 October 1986, a system of new eruptive fissures propagating from the SE Crater towards ENE (at elevations between 2900 and 2500 m) began to eject lava fountains, and lava flowed towards the floor of the Valle del Bove. At the same time a small pit crater (80 m in diameter) formed at about 2900 m elevation. Later that day the fissure system propagated further downslope towards ENE, and new eruptive vents became active at 2350-2200 m elevation, and explosive activity increased in the central part of the fissure system. A brief but violent eruptive episode occurred on 31 October at the SE Crater, resulting in the emission of a lava flow about 2 km long. While activity at the SE Crater gradually diminished to end on 2 November, the eruptiv fissures between 2200 and 2600 m remained active, and lava flows accumulated on the floor of the Valle del Bove to form a compound flow-field. A large pyroclastic cone built at the most vigorous explosive vent at about 2350 m, reaching a height of about 100 m; this was named Monte Rittmann in honor of the famous volcanologist who worked in Catania for many years and was one of the founders of the Istituto Internazionale di Vulcanologia (CNR, Italian Research Council).
The activity continued vigorously through the end of 1986 and then gradually decreased to cease completely on 27 February 1987. An area of 5.7 km² was covered with about 60 million m³ of lava; the farthest flow front had arrived at 1300 m elevation, 5 km from its source. The mean effusion rate for the eruption was 5.8 m³ per second. Furthermore some 2.4 million m³ of pyroclastics were ejected, mostly to form the large cone of Monte Rittmann.
Less than 2 months after the eruption a series of phreatic explosions occurred at the SE Crater, the Voragine and the Bocca Nuova. One of these, on 17 April 1987, killed two tourists and injured 7 others at the SE Crater. Two brief intervals of weak Strombolian activity occurred at the same crater in late-April and mid-May.

Maps and photos of the 1986-1987 eruption

1988-1989 SUMMIT ACTIVITY
Starting in April 1988, the summit crater complex reactivated with Strombolian activity in the Bocca Nuova, then at the Voragine, and - in October 1988 - at the SE Crater, while a small collapse pit formed on the floor of the NE Crater in June 1988. For the next 3 years this pit was the site of very hot gas emission, and continuous incandescence was visible within the pit.
Intracrater Strombolian activity continued at the Voragine and the Bocca Nuova through August 1989, while the SE Crater produced Strombolian activity at fluctuating levels, culminating on 15 April in the emission of a small lava flow (300 m long) from the SE Crater. On 4 May a powerful explosion occurred at the Voragine, and two still more violent eruptive episodes occurred from the same crater on 29 August and on 10 September, producing lava fountains and causing tephra falls on the E flank. The latter two events can be seen as a direct forerunner of the peculiar eruption at the SE Crater and on the ENE flank of September-October 1989 (see below).

1989 SE CRATER AND ENE FLANK ERUPTION
This eruption consisted of two distinct phases.
- First phase: 11-27 September. During this phase 14 episodes of vigorous eruptive activity occurred at the SE Crater. The first nine of these episodes were characterized by a gradual buildup from Strombolian bursts over increasingly violent explosions to spectacular lava fountaining and copious lava overflows from the crater. During the culmination of each episode eruption columns rose above the fountains, reaching heights of several kilometers, and tephra fell on the slopes of the volcano. Each episode lasted less than 2 hours, and between the episodes the crater remained almost absolutely quiet.
During the last five episodes, beginning on 24 September, the paroxysms were accompanied in their later stages by the fracturing of the SE Crater cone on its SE and NE slopes, giving minor fountains and copious lava flows. Lavas extended up to 3 km from the SE Crater, covering part of the Piano del Lago to the S and endangering the Torre del Filosofo mountain hut, and spilling down the W face of the Valle del Bove. An estimated 12 million m³ of lava were emitted during the 14 eruptive episodes, and the mean effusion rate during the paroxysms was estimated at 145 m³ per second (not considering the repose intervals between the episodes), and peak rates were surely an order of magnitude higher. The area covered with new lava was more than 3.2 km².
- Second phase: 27 September-9 October. On the evening of 27 September, eruptive fissures opened in the Valle del Leone (a subsidiary depression in the upper NW part of the Valle del Bove), at 2670-2550 m elevation, and lava began to flow SE across the Valle del Bove. Mild explosive activity (spattering) at the eruptive vents built a group of hornitos. Lava continued to be emitted at a fluctuating rate through 9 October when the eruptive vents became inactive. The flank eruption was accompanied by near continuous emission of blocks and ash from the SE Crater, which frequently mixed with Strombolian bursts, but no further lava emission took place at the crater. About 26.2 million m³ of lava were emitted from the flank fissure at a rate of 24.3 m³ per second, covering an area of 3.3 km². The farthest flow front stopped about 8 km from the vents at an elevation of 1100 m, about 2.5 km from the village of Milo.
Simultaneously with the opening of the eruptive fissures in the Valle del Leone - which were located on the ENE fracture system active in 1971, 1978, 1979, and 1986-1987 - a prominent fracture system began to extend from the SE Crater towards SE, first parallel to the SW Valle del Bove rim, and then running across the Schiena dell'Asino to the outer SE flank of Etna. Propagation of this fracture system continued from 27 September until 2 or 3 October when ground cracking was observed at about 1500 m elevation, 6.5 km from the SE Crater. No eruptive activity occurred from this fracture system, but concerns of a possible eruption were high during its formation, because lava would have rapidly reached densely inhabited areas from the lowest part of the fracture system.

Maps and photos of the 1989 eruption

1989-1990 SE CRATER ERUPTIONS
Following a quiet interval after the end of the 1989 flank eruption, the SE Crater became active again on 16 December 1989 with mild Strombolian activity. This activity continued with some fluctuations through the end of the year, and then culminated in an extremely violent paroxysmal episode early on 5 January 1990. This event dropped a continuous sheet of pyroclastics onto the main summit cone which was several meters thick on the S part of the main summit cone, and heavy tephra falls occurred to the NW, while a thin film of ash fell as far as the Aeolian Islands, up to 75 km from the summit of Etna. Thanks to a blizzard at the summit at the time of the event no people were in the danger zone, and the strong wind blew the plume to the NW, away from the Torre del Filosofo mountain hut which otherwise would have been buried. About 15 million m³ of pyroclastics were emitted during the 5 January 1990 eruptive episode, correspondig to an impressive mean eruption rate of more than 250 m³ per second (dense rock equivalent); a very small lava flow extended a few hundred meters to the S.
During the next month the SE Crater produced three further eruptive episodes that were much less violent but produced more lava. The longest of the flows produced during this period (on 15 January 1990) extended 2.5 km ESE into the Valle del Bove (to about 1780 m elevation). The last of these episodes, on 1-2 February, was followed by a brief interval of mild Strombolian activity between 27 February and 2 March, after which the SE Crater became quiet.

1990-1991 SUMMIT ACTIVITY
Between the summer of 1990 and the fall of 1991 most eruptive activity in Etna's summit area occurred at the Bocca Nuova where quite vigorous Strombolian activity (and minor intracrater lava emissions) occurred in July-August and November-December 1990, and in March and September-November 1991. A brief episode of paroxysmal lava fountaining occurred at this crater on 7 August 1990, and another episode of strong tephra emission occurred on 27 December 1990. Mild, intermittent Strombolian activity also took place in the Voragine in 1990 and 1991, and the NE Crater produced a very brief interval of mild Strombolian activity in May 1991. A significant increase in the activity of the Bocca Nuova and of the SE Crater occurred in early December 1991, heralding the onset of the major 1991-1993 flank eruption (see next paragraph).

1991-1993 SE FLANK ERUPTION
Accompanied by hundreds of small earthquakes, a system of eruptive fissures began to open on the upper SE flank early on 14 December 1991, between 3000 and 2700 m elevation; another minor fissure opened on the N slope of the SE Crater. Lava fountaining and emission of lava flows continued for a few hours from these fissures before activity ceased, but new eruptive fissures formed during the following night at 2340-2210 m on the SW wall of the Valle del Bove. These fissures were the site of vigorous Strombolian activity and immediately began to pour large quantities of lava onto the S part of the floor of the Valle del Bove. The new lava flow-field gradually extended to the E during the following weeks, and by the end of 1991 the farthest flow front was 5 km from the eruptive vents at about 1000 m elevation in Val Calanna, an arm of the Valle del Bove near the village of Zafferana. At this time explosive activity at the eruptive fissure had diminished, and it ceased altogether in mid-January 1992.
As a precaution to prevent the lava from advancing further towards Zafferana, a containment dike was built at the lower end of the Val Calanna in January 1992. For about two months the lava continued to accumulate in the S part of the Valle del Bove and in the Val Calanna, but in March the farthest flow front reached the base of the dike, and after this the basin behind the dike was gradually filled by overlapping tongues of lava. The first overflow over the crest of the barrier occurred on 7 April, and during the following days, lava began to spill rapidly down the steep slope above Zafferana, overwhelming three smaller barriers that were hastily erected to slow the advance of the lava. This flow stopped before reaching the first houses of the village, but in mid-May another flow ran down the same slope and extended about 120 m further than its predecessor, destroying a few isolated country buildings. During this period, much lava erupted at the main effusive vent travelled through a major lava tube system which allowed the lava to flow unusually far.
After the unsuccessful attempts to halt the advance of the flow by earth barriers and by dropping concrete blocks into a "skylight" (a "window" in the roof of the active lava tube), explosives were used to blast a hole in the side of the lava tube and to force the lava into an artificial channel where it would be subjected to more rapid chilling. The target was located very close to the main effusive vent. The main blasting operation was carried out on 27 May 1992, and most of the lava was diverted into the artificial channel, interrupting supply to the active flow front near Zafferana. The interventions to modify or halt the advance of the lava were made in an atmosphere of polemics, and the success and need of the operation were doubted by various scientists and organizations. It is true that after the final blasting operation no further lava flow advanced as far as those of April-May 1992, but this was largely due to the gradually diminishing effusion rate. After June 1992, all lavas accumulated in the upper part of the lava flow-field, where the total thickness of lava reached about 100 m.
The effusive activity continued until 30 March 1993, thus covering a time span of 473 days - the longest flank eruption at Etna since the mid-17th century. Estimates of the volume of the 1991-1993 eruption made after the cessation of the activity give between 205 and 250 million m³ of lava, making this the largest eruption (in terms of volume) since 1669. Nonetheless the eruption was generally characterized by a fairly low effusion rate: 5-6 m³ per second, although peak rates of 30 m³ per second were reported by some scientists. The area covered by new lava was 7.6 km².
The subsidence of the magma column in the central conduit system of Etna caused by the flank eruption led to major collapse in the Bocca Nuova and, more importantly, the NE Crater. These craters were the first of the four summit craters to resume eruptive activity when magma rose again to the surface in 1995.

Maps and photos of the 1991-1993 eruption

1995-2001 SUMMIT ERUPTIONS
The eruptive cycle initiated after the end of the 1991-1993 eruption is among the most complex events in the recent history of Etna, and it was followed by an even more complex flank eruption in the summer of 2001. All four summit craters produced spectacular and powerful activity, ranging from mild persistent Strombolian and slow effusive activity over lava fountaining to high-energy explosive episodes, and lava overflowed from all four summit craters as well as from fissures near the SE Crater.
The most significant events of the period 1995-2001 were the following:
- a series of 10 paroxysmal eruptive episodes at the NE Crater, followed by vigorous Strombolian activity and lava effusion between November 1995 and August 1996;
- a period of intense activity at the Bocca Nuova in July-December 1997;
- long-lived mild Strombolian activity and slow lava effusion at the SE Crater between November 1996 and July 1998;
- an isolated, short-lived but very intense eruptive episode at the NE Crater in late-March 1998;
- a period of spectacular eruptive activity in the Voragine in June-September 1998, culminating in a powerful eruptive episode on 22 July, and a slightly lesser one on 6 August;
- a series of 22 paroxysmal eruptive episodes at the SE Crater between September 1998 and February 1999;
- long-lived effusive activity from fissures at the SE and ESE base of the SE Crater cone between February and November 1999;
- a period of strong activity in the Voragine in July-September 1999, culminating in a very violent paroxysmal eruptive episode on 4 September;
- a period of spectacular eruptive activity at the Bocca Nuova in September-November 1999, culminating in a series of paroxysms and voluminous lava overflows onto the W flank;
- a series of 66 paroxysmal eruptive episodes at the SE Crater and related fissures between late January and late August 2000;
- a period of slow lava effusion from a vent ("Levantino") on the NNE side of the SE Crater cone (January-April 2001) followed by more rapid lava emission from the "Levantino" and mild Strombolian activity at the SE Crater summit vent (May 2001, including one more vigorous eruptive episode) and a series of 15 paroxysmal eruptive episodes (early June-mid-July 2001).
The total volume of lavas erupted between July 1995 and July 2001 is probably more than 100 million m³, and that of pyroclastics certainly exceeds 30 million m³. It is useless to calculate mean effusion or mass eruption rates for the whole period because many of the eruptive events were short-lived and had extremely high mass eruption rates, while other periods of activity were characterized by relatively regular, low effusion rates, as illustrated by two examples: during the persistent activity at the SE Crater between late 1996 and July 1998, the mean effusion rate was 1 m³ per second or less, while some 250 m³ per second were ejected during the 23 December 1995 eruptive episode of the NE Crater, and the peak eruption rates during the Voragine paroxysms of 22 July 1998 and 4 September 1999 were probably much higher.

Maps and photos of the 1995-2001 eruptions

2001 SUMMIT AND S-NE FLANK ERUPTION
Etna's first flank eruption of the new millennium was also one of the most complex eruptive events at this volcano in the past few centuries. First, it was not simply a flank eruption, because it involved some summit activity as well. Second, it occurred from seven different fissure systems located on the S and NE flanks of the volcano, each of which consisted of various clusters of vents behaving in a strikingly irregular manner. The fissures fall into two distinct groups, of which one is closely related to the Southeast Crater and can be described as lateral, while the other group was fed by a separate dike, furnishing an eccentric eruption. Some of the flank activity was unusually violent, with strong phreatomagmatic and magmatic explosions and abundant emission of pyroclastics. A dense ash plume drifted hundreds of kilometers away, mostly to the SE, causing heavy ash falls that disrupted air traffic in Catania and surroundings and provided a serious nuisance to the inhabitants of the region. One of the most amazing features of the eruption was the production of two different magmas at the same time, one (which was emitted from the lateral fissures) being similar to the magmas emitted during eruptions of the past three centuries, while the other (produced by the eccentric vents) was quite different from anything Etna had emitted for about 15,000 years.
In terms of monitoring, this was the best documented eruption of Etna so far. For years before there had been distinct signs of magma accumulation below the volcano, which indicated that it was recharging at a much faster rate than magma was being emitted from the summit craters at the same time. Dense networks of monitoring devices produced a steady flow of data before and during the eruption, aided by the most modern satellite-based monitoring techniques such as GPS and radar interferometry. The eruption was expected, even though the exact time of its occurrence remained unknown until a few days before its onset, but when it came it brought an unexpected number of surprises.
The July-August 2001 eruption was certainly a dangerous one and it did cause significant damage, mostly to the cable car and ski lifts located between 1900 and 2600 m on the S flank of the volcano. Yet it was not the devastating event it appeared to be from what was said and written in the international mass media. The much-publicized "serious threat" to the town of Nicolosi was essentially an invention of reporters in need for a new scoop after several days of violent clashes and riots in the Italian city of Genoa during the G8 summit. In the end the eruption ceased much earlier than anyone would have expected, making this at best a medium-sized Etnean eruption in terms of volume. A total volume of about 30 million m³ of magma was emitted as lava (about 25 million m³) and pyroclastics (5-10 million m³), one-seventh of the volume of the 1991-1993 eruption. The area covered by new lavas is about 5.5 km². Eruption rates were moderately high during the first two weeks of the eruption, peaking at about 16 m³ per second. The eruption lasted from 17 July to 9 August 2001, but the most vigorous and spectacular activity was over by the beginning of August. The 24 days of activity, however, were enough to modify the morphology of the S flank significantly. The most spectacular products are the large pyroclastic cones that grew at about 2500 and 2100 m elevation.

Map, photos and description of the 2001 eruption

2002-2003 NE AND S FLANK ERUPTION
Preceded by surprisingly little warning (clear premonitory seismicity began only two hours before its beginning), a new eruption started early on 27 October 2002 from two fissures on the NE and S flanks. Like the 2001 eruption, this one consisted of lateral activity on the NE flank and eccentric activity on the S flank. Eruptive activity on the NE flank lasted until 5 November and caused the nearly total destruction of the tourist and skiing facilities of Piano Provenzana. On the S flank the activity was highly explosive and generated heavy tephra falls mostly in the southern and southeastern sectors of the volcano, nearly paralyzing public life and traffic in Catania and surrounding areas. Lava was produced on the S flank between 28 and 30 October and again starting on 13 November, and activity there continued with some variations through 28 January 2003. An enormous pyroclastic cone grew about a cluster of very closely spaced vents located at 2750 m (pre-eruption) elevation. Between 25 November and 10 December, the explosive activity shifted a little upslope to 2800 m, and a second pyroclastic cone was formed, whose northern base completely buried the Torre del Filosofo mountain hut. There were four main surges of lava advancing on the southwestern and southern flanks in November and December. The south flank surges seriously threatened the tourist facilities around the Rifugio Sapienza and destroyed a few buildings (the "Rifugio K", the tourism agency building of the Province of Catania, and the "Esagonal" restaurant); furthermore, a section of the Provincial Road 92 connecting the Rifugio Sapienza area to the town of Zafferana was buried by a lava flow in mid-December.
Preliminary estimates of the volume of emitted products give a total volume of about 30 million m³ of lava and about 40 million m³ of pyroclastics, making this one of the most explosive flank eruptions of Etna of the past 350 years. Only about 10 million m³ of lava and a very little tephra were emitted during the brief Northeast Rift activity, representing less than 15 per cent of the total volume. The explosive activity on the S flank built two large pyroclastic cones, the larger of these standing up to 200 m above the pre-eruption surface, and thus dwarfing the largest cone formed during the 2001 eruption. If the morphological changes caused by the 2001 eruption were spectacular, those produced by the 2002-2003 eruption are overwhelming. Smaller (but nonetheless impressive) cones and spatter ramparts were built by the activity on the NE flank.
During the first days of the eruption vigorous seismicity and extensive ground deformation occurred on the NE and E flanks of the volcano, causing significant damage to man-made structures (roads and buildings). These were related to the instantaneous slippage of a large sector of the eastern flank of the volcano, a process that is not new at Etna but had not occurred since 1988 and in the past had not been of the same dimensions as this time. As of August 2003, slippage of the unstable flank continues, though at a much diminished rate compared to the up to 2 m of horizontal movement observed during the early days of the eruption in the upper portion of the mobile sector. The 2002-2003 eruption (along with the 2001 eruption) is clearly the best documented of all Etnean flank eruptions for the wide variety of geophysical and magmatic processes captured by an ever more sophisticated network of monitoring instruments.

Map, photos and description of the 2002-2003 eruption

Copyright © Boris Behncke, "Italy's Volcanoes: The Cradle of Volcanology"