Typical "persistent" activity at the SE Crater on 5 August 1997: Strombolian explosions occur from a small cone on the crater floor, and lava pours from a vent from the cone's flank (at left). This view which was taken from the NW rim of the crater shows the lights of the towns on the E coast of Sicily in the background, with a part of Catania at the extreme right. The bright dot visible in the uppermost part of the photo (only in the enlarged version) is Venus

The SE Crater from 1995 to 2001

The activity of the Southeast (SE) Crater between 1995 and 2001 can be divided into several periods, each of which was characterized by a distinct behavior. Eruptive activity began on 6 November 1996 after about five years of quiescence and more than one year after the beginning of activity at the Bocca Nuova and the NE Crater.

1st period: November 1996-July 1998

From its reactivation in early November 1996 until late-July 1998, the SE Crater was the site of classical persistent activity, with Strombolian activity from the summit of an intracrater cone accompanied by slow lava effusion from vents on the flanks or at the base of the intracrater cone. Apart from relatively minor fluctuations in the intensity, this activity went on for 20 months in a strikingly regular manner, contributing to major growth of the SE Cone.

Until 19 July 1997, all lavas emitted from the effusive vents remained confined to the crater depression left after the major 1990 eruptions, but starting in the evening of that day, lava began to spill over low points on the crater rim, first towards SE and later also to the NE. By December 1997 the crater depression had been filled almost completely; the summit of the intracrater cone stood about 30 m above the highest point of the crater rim, and lava began to spill over the crater rim in many places towards SE, S and SW. Most overflows were quite short-lived, lasting a few hours to two days, and stopped as soon as the lava flow front arrived at the base of the SE Crater cone. Only a few flow lobes extended beyond the base of the cone, interestingly these were all emplaced on the SW flank, and reached maximum lengths of about 0.5 km.

During certain periods magma intruded into the intracrater cone itself without being ejected by its explosive activity, but deforming it to assume the classic shape of a lava dome in April-May 1997, while later the deformation was more asymmetric and caused protrusions and bulges on the flanks of the cone, most notably in May 1998. In some cases the injection of magma preceded the opening of new effusive vents on the flanks or at the base of the cone, in others it did not, and the magma remained below the surface. These processes were among the most peculiar observed during the current eruptive cycle and had never been observed before.

After the end of the first eruptive period in late-July 1998, the simple saucer-shaped, ca. 150-m wide crater produced by the early 1990 activity was brimful, with only a minor part of the western and northwestern crater rim standing a few meters above the intracrater lava field. Lava had spilled over, and buried, the crater rim on all sides except the west and northwest, and a chaotic, rugged lava field with numerous overlapping and frequently channelized flow lobes had developed in the central part of the crater, surrounding the intracrater cone that was the site of Strombolian activity. The highest point of this cone stood at about 3220 m, some 35-40 m higher than the formerly highest point on the northwestern rim of the SE Crater.

Interestingly, the activity of the SE Crater ceased a few days after the large 22 July 1998 paroxysm from the Voragine, possibly as a result of pressure relief from the central conduit system; this clearly indicated that the conduits of these two craters were connected at some depth. The SE Crater remained absolutely quiet for six weeks while the Voragine and the Bocca Nuova showed continued vigorous activity that began to diminish only in early September 1998.

2nd period: September 1998-February 1999

A new eruptive period of the SE Crater began in mid-September 1998 and continued until early February 1999; during this period, the activity consisted of 22 violent eruptive episodes occurring at intervals lasting from a minimum of 2 days to a maximum of 15 days. During the first three months of this period the interval between eruptive episodes became longer in a strikingly regular manner, so that the time of the next eruptive episode could be predicted with unprecedented precision. No correlation, however, was observed between the length of a quiet interval and the following eruptive episode. On the other hand, the evolution of each eruptive episode followed a strict scheme, starting with mild Strombolian activity, which increased during the next 10-24 hours and culminated with copious lava outflow and near-continuous jetting of lava to 200-300 m above the vent. In at least one eruptive episode (on 24 October 1998) a small vent was active besides the main vent at the summit of the rapidly growing active cone. During the quiet intervals, the activity at the SE Crater decreased to zero, and it was possible to approach right to the rim of the eruptive vent at its summit.

Starting in January 1999, the repose intervals between the eruptive episodes became again shorter, and at the same time the episodes themselves became much more violent, and the buildup periods at their beginning shortened from a few hours to only 15 minutes. These episodes produced a significantly higher amount of pyroclastics than the earlier ones, and some generated eruption columns several kilometers high, small slides of loose material on the flanks of the cone, and in at least one case, small mudflows. The last seven eruptive episodes occurred on 5, 9-10, 13, 18, 20 and 23 January, and on 4 February 1999. It was during this latest episode that the behavior of the SE Crater changed dramatically.

The activity between 15 September 1998 and 4 February 1999 caused more notable morphological changes than the preceding eruptive period of November 1996 - July 1998. The former intracrater cone grew to fill virtually all of the former crater area and its flanks merged completely with the outer flanks of the pre-1997 cone of the SE Crater. The height of the new summit of the SE Crater rose to more than 3250 m, and the crater is now about 30-40 m wide, much larger than the vent of the 1996-July 1998 activity, but notably smaller than the crater was before 1997. The rapid growth of the cone was seen as closely related to the characteristics of the later eruptive episodes - the higher the cone grew, the more violent became the paroxysms, and it was suspected that sooner or later the cone would not resist any longer to the magma pressure within the conduit. Each time more pressure was needed to bring the magma to the summit of the cone for eruption, and therefore the violence of the paroxysms increased.

3rd period: February-November 1999

On 4 February, the last paroxysm began just like those before, with an initial short period of discrete Strombolian explosions which gradually became stronger and more frequent, until they merged into a fluctuating lava fountain jetting 100-150 m above the vent. After about 30 minutes of such activity, the cone burst open low on its SE flank, and a powerful, broad lava fountain shoot vertically from the new vent, while the summit vent became inactive, and then a fracture began to split open downslope, to the base of the cone, where the activity continued even when the large fountain from the new vent on the flank began to subside. The paroxysm thus ended after less than one hour, but mild eruptive activity - ejection of lava blobs and effusion of lava flows - continued at the lowermost part of the new fracture (named 4 February fissure hereafter). During the following days, lava spilled down the steep W slope of the Valle del Bove, and a broad, complex lava flow-field began to form. The longest flows reached the floor of the Valle del Bove, near the Monti Centenari, about 2.5 km from the eruptive vents. During the first month of the activity, a group of "hornitos" (small, steep-sided cones formed by the accumulation of fluid, welded lava blobs immediately around the vents) grew in the upper part of the fissure while degassed lava was emitted from several vents slightly further downslope.

The beginning of the activity from the 4 February fissure was immediately followed by a subsidence of the magma column within the Bocca Nuova, and neither the SE Crater itself showed any further activity for exactly 7 months. Nonetheless, the activity of the new fissure was very closely related to this crater, and is interpreted as a simple replacement of the previous activity at the SE Crater. Rather than rising to the summit of its cone, the magma had found a new outlet much easier to arrive at (because situated about 250 m lower), and in some respects, the activity at the new fissure marked a return to the relatively quiet eruptive conditions that had prevailed during the first eruptive period at the SE Crater, between late 1996 and July 1998. The effusion rate, though, was significantly higher - at least 5 m³ per second, compared to less than 1 m³ per second during the period between November 1996 and July 1998 - during the first six weeks of the activity; afterwards it showed a slow decrease, and much of the lava flowed through tunnels. For about one month between mid-April and mid-May, the lava did no longer arrive at the surface at the 4 February fissure, but travelled through a tunnel for more than 1 km before issuing from secondary vents in a nearly inaccessible area on the steep W slope of the Valle del Bove.

From mid-May on, effusive vents were again active near the hornitos of the early phase of the activity, and for the next three months the intensity of the activity and the effusion rate underwent notable fluctuations. The lava flow-field grew mostly in thickness, since little new lava extended beyond its margins, and repeatedly more gas-rich magma arrived at the surface, causing mild explosive activity and the growth of new hornitos near the effusive vents. The return of more explosive activity in late June coincided with the reactivation of the summit craters (except the SE Crater) and probably reflected the arrival of fresh magma with a higher gas content.

Effusive activity from the 4 February fissure ended on 25 August, at a time when the Voragine increased its activity, but only two days later, new eruptive vents became active some 50 m to the north of the 4 February fissure, and lava flowed towards the Valle del Bove along the N margin of the earlier lavas. This activity appeared to be rather weak compared to the early stages of the activity initiated on 4 February, and little detail is known about its course during the days preceding the eventful afternoon of 4 September. However, some flowing lava was apparently seen at about the time of the beginning of the Voragine paroxysm of 4 September by a group of visitors who then narrowly escaped from a rain of large blocks and bombs.

That evening at about 2045 h, just as the paroxysm from the Voragine was over, Strombolian explosions started at the summit vent of the SE Crater. This activity did not culminate in a true paroxysm like those of the winter of 1998-1999, but after 90 minutes or more, the main 4 February vent on the SE flank of the cone reactivated, pouring a minor lava flow in the direction of the hornitos of February-March 1999, before the activity concentrated at the 27 August vents. Lava supply from these vents was considerably higher on 5 September than during the preceding days.

Between 5 and 11 September lava continued to flow from the 27 August vents, but on the 12th, new vents opened about 200 m further to the E, and mild explosive activity built hornitos there while lava began to advance in the direction of the Valle del Bove. For the next nearly two months effusive activity from these vents continued, with fluctuations in the effusion rate, and occasional flurries of minor explosive activity leading to the growth of new hornitos - most notably on 24-25 October and 1 November 1999. During the first week of November, the activity began to diminish notably, and the last time flowing lava was seen near the SE Crater on 12 or 14 November. The long-lived effusive activity initiated on 4 February thus ended after 9 months, and after the emission of more than 40 million m³ of lava, quite a large volume for a summit eruption.

4th period: January-August 2000

The SE Crater returned to spectacular life early on 26 January 2000 with an episode of lava fountaining that culminated in the opening of a new fracture on the S flank of its cone. While for one day it seemed as though a repetition of the events of 1999 had begun, lava effusion from the new fracture ceased during the following night and the crater fell into complete silence. On the morning of 29 January, another paroxysm took place which was very similar to its predecessor but lasted much shorter, and this was followed two days later by yet another paroxysm. Meanwhile it became clear that during these paroxysms not only the southern side of the SE Crater cone fractured, but also the NNE side, so that the cone was cut by a continuous fracture from NNE to S, and activity occurred along the whole length of this fracture.

Then the events accelerated in an unprecedented manner. Brief, but extremely violent episodes of lava fountaining followed each other at a frantic rate of one to three per day, and by 20 February, 35 (thirty-five) such events had occurred (a complete list of paroxysmal eruptive episodes is given on a separate page). Nearly all of them were characterized by a surprisingly fixed sequence of events: after hours of total quiet, lava began to issue from a vent at the lower end of the NNE fracture. The output of lava at this site increased rapidly during the following 10-30 minutes and eventually spattering began at the vent; then the spattering would gradually pass into lava fountaining and more fountains would spring up in progressively higher locations along the fracture until the activity reached the summit vent (or vents). Activity there initially consisted of discrete Strombolian bursts, which gradually became stronger and more frequent until they blended into a continuous uprush of lava fragments - a lava fountain, which in nearly all cases rose hundreds of meters above the summit of the SE Crater cone and at times even surpassed 1000 m in height. The fountaining stage almost always coincided with the reopening of the fracture on the S flank of the cone. Towering columns of ash and gas rose several kilometers into the sky, and heavy lapilli falls occurred in areas located downwind from the volcano. The culminating phase always lasted 10-15 minutes and then stopped abruptly, being followed by Strombolian bursts and/or ash emission of decreasing strength and a rapid decline in lava emission; usually the crater was perfectly quiet within 15-30 minutes after the end of lava fountaining. A particularly violent paroxysm that occurred on 15 February is shown in a series of video clips on a separate page.

After 20 February the intervals between eruptive episodes grew longer, and the character of these events began to show some significant changes. Several well-defined craters developed at the lower end of the S flank fracture, as the activity during the paroxysms focused more and more on those vents. In early March a low shield began to build around the lowermost of these vents, which eventually was informally named "Sudestino", after a similar feature that formed in 1970 at the NE Crater and was named "Nordestino" (little North-east). The Sudestino became the main eruptive vent at the SE Crater during the eruptive episodes of 12, 14 and 19 March and grew significantly during these events, while activity at the summit of the SE Crater cone mainly consisted of ash emission, and the NNE fracture remained inactive. Then, on 22 March, the main focus of activity shifted back to the summit vent and paroxysms became again similar to those of early-mid February; the Sudestino did not participate in the paroxysms of 22, 24 and 29 March and 1 and 3 April. On 6 April, the S fracture remained closed during a paroxysm, but this event was followed by slow lava extrusion from the Sudestino.

One of the most peculiar paroxysms of the entire series occurred on 16 April. This was the 50th paroxysm since 26 January, and it seemed as though the SE Crater intended to celebrate this event in a particular manner. Activity began late on 15 April with lava extrusion and Strombolian explosions from the Sudestino, which continued through the forenoon of the following day and gradually increased toward noon. It was a fine Sunday and many people had climbed Etna to watch the display from close-up; furthermore the good visibility allowed observations even from distances of tens of kilometers. Beautiful lava fountains developed at the Sudestino shortly after noon, which were accompanied by Strombolian bursts from the summit vent of the SE Crater. For about two hours it seemed as if this was already the culmination of the activity, but then all of a sudden the southern flank of the SE Crater cone exploded, and a small pyroclastic flow rapidly expanded from the cone toward SW. Fortunately it was deflected by the Sudestino into this direction, otherwise it would probably have extended toward S, right in the direction of the Torre del Filosofo mountain hut where dozens of spectators were watching the show. A general flight ensued, with people running down the slope below the mountain hut to escape from a situation that seemed to get out of control. Behind them a dark eruption column majestically rose about 6 km into the clear blue sky as the summit vent of the SE Crater had taken over the role of the main eruptive center. No further pyroclastic flows occurred, and the continuous uprush of tephra continued for about 25 minutes before the paroxysm ended from one moment to another. After that day the Sudestino never showed any signs of eruptive activity again.

Between 6 April and 15 May the repose periods between eruptive episodes were amazingly regular, lasting 9-10 days. Apart from that of 16 April, the paroxysms were essentially similar and resembled much those of late March, although the eruptive activity at the southern fracture was restricted only to its uppermost part. On 15 May, two paroxysms occurred within 12 hours, then the interval again lengthened and the next paroxysms occurred on 18, 20, 23 and 27 May. Two paroxysms occurred again within 12 hours on 1 June (of which the second was one of the most violent of the whole series), which were followed by further similar events on 5, 8 and 14 June. During the last two of these tephra was distributed over the N flank of Etna, which until then had been spared by tephra falls (the most frequently affected sectors were on the NE, E and SE sides of the mountain). Then, after a quiet interval of 10.5 days, the SE Crater produced its final show on the late evening of 24 June with a powerful paroxysm (the 64th since 26 January) that was extremely well visible due to extraordinarily clear weather, and thousands of people decided to forego their visits to discotheques and parties and rather go to "see the lava". Rarely have the roads leading to Etna been seen so crammed with traffic as on that evening! Above all this a brightly yellow lava fountain jetted up to 1200 m from the summit of the SE Crater cone while a lava flow extended 3 km down to the floor of the Valle del Bove. The onset of lava fountaining had been incredibly sudden, and in the same instantaneous manner the fountain disappeared after 15 minutes of illuminating the sky over eastern Sicily. While the fountaining had been accompanied by a continuous loud roaring, the noise level increased after the end of fountaining (due to violent degassing) and culminated in a series of detonations as the gas jet exceeded the speed of sound. A sound clip, movie clips and photographs of this event are available on a separate page.

A number of accidents that occurred during some of these latter paroxysms aroused significant concerns about safety issues. On 26 April an airplane encountered falling scoriae while flying under a plume produced by a paroxysm shortly before and had to make an emergency landing at the airport of Catania. Nine days later a German tourist who had remained near the SE Crater to see a paroxysm was reported missing; this man was luckily found alive during the following night. One man was slightly injured by falling scoriae on 16 April at a distance of about 6 km from the SE Crater, and similar cases were reported from other paroxysms. Yet the impressive lava fountains recurring at intervals of a few days, and the fact that they were preceded in all cases by clear premonitory symptoms, attracted numerous people. The fact that no one was seriously injured or killed during the paroxysms of 2000 must be considered a miracle.

Significant damage was caused by the recurrent tephra falls over inhabited and cultivated areas. On some occasions scoria clasts up to 5 cm in diameter fell on villages 8-10 km from the SE Crater. The state of emergency was declared in the spring of 2000 for an area on the E flank of Etna. Yet the tephra proved to be an efficient fertilizer, as much of the fertility of the Etna area is due to volcanic soils and frequent tephra falls.

The SE Crater remained perfectly quiet (except for intense fumarolic activity) between 24 June and 26 August. Then lava emission from the fracture on the NNE flank of the SE Crater cone resumed, and a new paroxysm occurred on the morning of 28 August, which was similar to those of June except that no activity occurred on the S flank fracture. 24 hours later, another paroxysm occurred, but this was much less intense than its predecessor. This 66th paroxysm in little more than 7 months was the last in the unprecedented series of lava fountains of 2000.

5th period: November 2000-July 2001

The SE Crater remained totally quiet for about 3 months, but in late November it seemed as though it was to return to its former vigor when lava began once more to extrude from the lowermost vent on the NNE flank fissure. For about one week a small lava flow was fed from this vent, but then the activity subsided without ever having developed into a paroxysm.

Seven weeks later, on 20 January 2001, the same vent on the NNE flank of the SE Crater cone became active again. Like in late November, lava was slowly extruded from this vent to form a small flow about 100 m long. But this time the activity did not cease after a few days, but it continued day after day, week after week, and gradually the effusion rate increased. Furthermore there were moments when the summit vent of the SE Crater displayed weak Strombolian activity; however, nothing similar to the paroxysms of the previous year ensued. In late April, mild spattering began to occasionally accompany the lava outflow, which at the same time significantly increased in its rate. Starting on 6 May, Strombolian activity at the summit vent of the SE Crater intensified and culminated two days later in a new episode of intense activity, although no true, continuous lava fountains developed in this event. During the following month mild Strombolian activity at the summit of the SE Crater was almost continuous though with some fluctuations, and vigorous effusive activity occurred at its satellite vent on the NNE flank. Lava flows extended up to 2.5 km toward the Valle del Bove, while the effusion rate at times exceeded 10 cubic meters per second, about 100 times higher than during the first days of the 2001 activity. This relatively harmless style of activity attracted many visitors who had to hike a long, difficult track to the nearly inaccessible N side of the SE Crater, but they were rewarded by a beautiful spectacle. Lava often ran in cascades down the flanks of a steep cone that had built around the active vent (this was eventually nicknamed "Levantino"; this might be roughly translated into "little thing lying in the direction of the sunrise"), and above this the main vent of the SE Crater produced intermittent weak Strombolian bursts. With this beautiful and innocuous activity, the tourist season of 2001 appeared highly promising, and a tortuous footpath was established between the SE Crater's northern side and the Pizzi Deneri, with the intention to guide tourist groups to the area of the activity. Only one group of tourists was lucky enough to enjoy the sight close-up. Then the SE Crater once more changed its behavior.

While lava emission was seen to be unusually vigorous on early 5 June, the following evening all activity had completely stopped, but lava effusion resumed during the night of 6-7 June and was soon accompanied by vigorous Strombolian bursts from the summit of the SE Crater cone. This was the start of a new eruptive episode, the first of fifteen that would characterize the activity at the crater for the next six weeks. The 7 June paroxysm was relatively weak in comparison with those of the preceding year, but its successors gradually became stronger, with spectacular lava fountains from both the Levantino and the summit vent and emission of voluminous lava flows toward the Valle del Bove. Tephra generation was much less significant than during the eruptive episodes of 2000. Another peculiarity of these eruptive episodes was that the fracture on the S side of the cone remained inactive, but at times lava fountains played from numerous vents along the NNE fracture. The Levantino grew impressively and became a distinct morphological feature of the ever more complex summit area.

The 14th eruptive episode, on early 13 July 2001, was immediately followed by an intense swarm of small to moderate earthquakes that were clustered below the S flank of Etna and were accompanied by rapid inflation and ground fracturing in the area of the Montagnola, a large pyroclastic cone formed during a 1763 flank eruption. These were actually the signals sent out by a dike that was pushing toward the surface in that area, which apparently left the SE Crater fairly unimpressed because after four days of quiet it produced yet another spectacular paroxysm early on 17 July. A few hours later, magma began to erupt from a new fissure at the SSE base of the SE Crater, immediately below the Sudestino, and the July-August 2001 flank eruption had begun.

After the intense activity during 1996-2001, the SE Crater had changed beyond recognition. From a low, broad hump built up during the 1989-1990 eruptions, it had evolved into an elegant, symmetrical cone whose summit stood about 120 m above the highest point of the crater before the initiation of activity in 1996. Seen from S and E, this cone appears higher than the old central cone, although this is only an effect of perspective; actually it is still some 20 m lower than the highest point of Mt. Etna. With its regular cone it forms a miniature stratovolcano whose simple morphology belies its complex evolution in the eventful years of 1995-2001. On its NNE flank the symmetry is broken by the steep satellite cone of the Levantino, while its southern counterpart, the Sudestino, forms a more detached feature. As of early 2004 the SE Crater is quiet, but it is all but certain that it will become active again in the near future, its cone will experience further growth, and thus the SE Crater seems to be destined to become the new summit of Mt. Etna unless some catastrophic event will remove its upper portion.

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