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Sketch map showing the distribution of pyroclastics of the 4 September 1999 eruption of the Voragine, based on field work during the week following the eruption. Click on the map for an enlarged version.

Sketch map of the summit craters of Etna, based on fieldwork made between 7 September and 1 October by Behncke and others.

1 October 1999 visit to the summit craters. The summit area of Etna was visited by Boris Behncke (Dipartimento di Scienze Geologiche, Catania University), Roberto Scandone and Lisetta Giacomelli (Dipartimento di Fisica, Università "Roma Tre"), and Angelo Amara (Catania University) on 1 October 1999. Strong explosive (Strombolian) activity at the Northeast Crater prevented the group from climbing on its cone: every few minutes bombs were ejected up to 100 m above the crater rim, and many fell onto the SW and S flanks of the Northeast Crater cone, to as far as 100-150 m away. Besides these larger explosions, loud roaring noise was almost continuously heard from the crater, and emissions of ash were frequent.
The western rim of the Voragine could be approached relatively easily, and it was possible to look into the crater with its large pit formed during the 4 September eruptive episode. No significant activity occurred during about 10 minutes of observation. The Bocca Nuova was also quiet, with only some gas emission from the northwestern vent which had produced the latest major activity of the Bocca Nuova, on 20 and 21 September. A roughly circular area of subsidence was present on the southern side of this vent; subsidence had occurred at the same site in January-April 1998 and in October 1998.
The map of the summit craters shown above was drawn after fieldwork on 28 September and 1 October; while relatively accurate for most of the area, the eastern flank of the Voragine has been investigated less thoroughly due to the presence of dense gas plumes drifting over that area. The map will be updated if significant corrections are necessary.

Report on a 28 September 1999 visit to the summit craters. Detailed observations of the Northeast Crater, the Voragine and the Bocca Nuova were made during a summit visit by Boris Behncke (Dipartimento di Scienze Geologiche, Catania University) on 28 September 1999. These observations yielded further detail about the effects of the 4 September Voragine eruption and of the activity since then.
Northeast Crater. The entire Northeast Crater cone received heavy fallout of bombs from the Voragine, and any trace of the footpath that existed on its W side before that eruption has vanished under a continuous cover of bombs, some up to 1.5 m in diameter. The configuration of the crater itself has not changed much as far as could be ascertained; however, a part of the crater area was veiled by dense, dark brown to black ash plumes that were emitted from the active central pit of the crater. A few fresh, black bombs with a maximum diameter of 0.3 m were lying on the W side of the cone and more were present on the W and SW crater rim; these had been ejected by Strombolian activity in the past few days. The collapse scar on the SW flank of the cone, formed during the 22 July 1998 eruption of the Voragine, had been largely healed by abundant bomb fallout from the 4 September 1999 eruption, but on the SSE side a further portion of the cone's flank had collapsed, leaving a similar scar. The eruptive activity within the active central pit consisted of near-continuous expulsions of dark ash, and while standing on the rim of the pit, Behncke heard frequent loud rumblings and the falling of rocks within the pit. Differently from the incandescent ejections of the preceding days no incandescence was seen during the 28 September visit, and virtually no view of the interior of the pit could be obtained. However, good views were obtained by Charles Rivière on 25 September, and these show that the pit continues to a depth of several hundred meters with vertical walls, its floor being invisible.
Voragine. A good panoramic view of the Voragine from the S rim of the Northeast Crater revealed that the morphological changes caused within this crater by the 4 September eruption were less pronounced than had appeared from the descriptions of various people who had visited the crater during the previous days. The former "diaframma" and central vents had merged into one large crater about 200 m wide, but it appeared that there were still two eruptive centers at depth within this crater, whose positions coincided with those of the former vents. Photos taken by Charles Rivière on 25 September during a close approach to the crater show its interior part to narrow at depth. The carving out of the new large crater within the Voragine probably produced all the lithic blocks that were ejected together with the more abundant fresh bombs on 4 September. On the SW rim of this crater, a wide U-shaped gap had formed in the former "diaframma" through which the crater floor of the adjacent Bocca Nuova could be seen.
To the E and SE the new crater was surrounded by a fairly flat and smooth area, similar to the crater floor on that side before the eruption; the adjacent outer crater rim was much gentler than before. To the N, NW and W the terrain was heavily fractured, but gas came from these fractures which were oriented more or less concentrically. Similar sub-concentric fractures were present on the outer ENE and E rim of the Voragine and on a ridge which now constitutes both the SE flank of the NE Crater cone and the NE rim of the Voragine.
A rootless, fountain-fed lava flow had formed during the 4 September eruption on the W side of the Voragine as fluid ejecta accumulated rapidly on the crater rim and the outer slope below. The upper part of this flow was extremely craggy and heavily fractured; further downslope its surface was composed of large, reddish brown blocks, similar to the lava flow emitted on 22 July 1998 from the same crater. The flow was up to 150 m wide in its upper part but narrowed to about 30 m in its distal portion where it formed a lobe along the northern side of the 22 July 1998 flow; the new lobe, however, was shorter than its predecessor.
Two fountain-fed lava flows also formed on the E side of the Voragine. They were essentially similar to the W flow but narrower. The longer of these flows extended about half way down the slope towards the W rim of the Valle del Bove. The source area on the W rim of the Voragine was strongly fractured, with some of the fractures being up to 2 m deep.
Eruptive activity within the Voragine during the 28 September visit consisted of frequent loud explosions deep within the newly formed crater, roughly in the location of the former central vent. No pyroclastics were seen to rise to the lip of the crater although the noise of rocks falling back into the active vent could be frequently heard. No fresh ejecta were found while walking on the E and SE rim of the crater.
Bocca Nuova. This crater has changed most since last seen by Behncke on 28 July. About 90 per cent of the crater floor are covered with new lava which has buried most of the two eruptive sites that had existed for at least four years in the NW and SE of the crater. It is not clear if any of the lava originated at the Voragine during its 4 September eruption - one might suspect some lava inflow from there because the lava surface is clearly higher towards the Voragine than in the SW and S part of the Bocca Nuova. There are, however, no confirmed observations of lava within this crater immediately after the 4 September event. The surface structure of the lava is similar to that of the lava which was seen on the floor of the Bocca Nuova in August 1998, possibly emplaced during the 22 July 1998 eruption of the Voragine. In late July 1999 the two eruptive centers on the crater floor were surrounded by low, broad pyroclastic cones; of these only the one in the SE was seen to protrude partially from the new lava during the 28 September visit. The SE vents themselves have completely disappeared under the lava and have apparently not erupted since then, but profuse steaming occurred from the margins of the lava fill. At the site of the NW vents there was an irregularly shaped, shallow depression that weakly emitted yellowish gas from several fumaroles; no eruptive activity occurred during the visit, and none had apparently occurred for several days before.
It appears that a portion, maybe several tens of meters wide, of the W rim of the Bocca Nuova collapsed, enlarging the crater and lowering the rim on that side. The lava surface on the crater floor lies only about 30-40 m below that rim. In general, the Bocca Nuova is significantly shallower in its NE, N and NW parts while its depth is greatest in its SE part where the floor may have been raised by no more than 10 m.
Bombs that were a few days old littered most of the crater rim on the S and SW side; these appear to have been ejected during the vigorous activity on 20 and 21 September. Many actually fell as far as the S and SW flanks of the main summit cone.
No close observations were made of the Southeast Crater and its cone and of the area of ongoing effusive activity on the ESE base of the cone. Photos taken by Charles Rivière on 25 September show an irregular lava surface on the floor of the Southeast Crater, and many incandescent spots and holes in that surface. Effusive activity was reportedly continuing on 28 September, with small active lava flows accumulating around the vents that became active on 10 or 11 September.

Recent Etna photos (20-25 September 1999) All photos are courtesy of Charles Rivière (Tremblay-en-France, France)
Mild explosive activity at the newly formed hornitos on the ESE base of the Southeast Crater cone, photographed on 20 September.
Effusive vent producing a lava flow, accompanied by vigorous spattering, in the area of effusive activity on the ESE base of the Southeast Crater cone. Photo was taken on 20 September.
Two views of the active central pit of the Northeast Crater as seen from its E or SE rim on 25 September. The left photo shows the pit during particularly clear viewing conditions while in the right photo ash is rising from the floor of the pit.
Left: A view onto the floor of the newly formed crater in the Voragine as it appeared on 25 September, with an active vent located in approximately the same position as the former central vent. Depth of the crater is more than 150 m. This photo was probably taken from the W rim of the crater. Right: Magma bubbles exploding in two vents at the NW eruptive site within the Bocca Nuova on the evening of 19 September, shortly before a paroxysmal eruptive episode on the next morning.
Left: Similar view to previous photo, Bocca Nuova, 19 September. Right: The northern part of the Bocca Nuova seen from the W crater rim on 20 September, a few hours after the eruptive episode of that morning. The crater is flooded with fresh lava which has mostly buried its source vent (located where the gas column is issuing). This photo shows the "diaframma" with the newly formed breach in the center background and the western face of the Northeast Crater cone in the far left.
Left: Explosive burst from the NW vent of the Bocca Nuova on 20 September. Right: Northern part of the floor of the Bocca Nuova seen from W crater rim on 23 September. The NW vent area appears as an irregularly shaped depression in the center of the photo; there is no visible activity. The "diaframma" is visible in the upper center of the photo.
Left: The northern part of the Bocca Nuova as seen from the W rim of the crater on 23 September, showing the "diaframma" and the Northeast Crater cone in the background. Right: Lobe of lava erupted on 20 September that flowed into the depression around the SE vent area in the Bocca Nuova, photographed on 23 September. Note the profuse steaming on the flow margins.
The crater floor of the Southeast Crater, seen on 24 September. Incandescence is visible in numerous spots within the lava that remained on the crater floor after the activity of 4 September.

27 September update. During the past week, eruptive activity has continued in Etna's summit area. The most persistently active of the craters has been the Northeast Crater which had deep-seated Strombolian activity within its central pit. Marco Fulle (from the Astronomical Observatory of Trieste) observed ejections of incandescent bombs on 22 and 26 September, some up to one meter across, to several tens of meters above the lip of the pit, but all ejecta fell back into the pit. Similarly, Charles Rivière (of Tremblay-en-France, France) observed incandescent ejections from the Northeast Crater up to 80-100 m above the pit's rim on 25 September.
The Voragine was visited by Fulle on several occasions between 22 and 26 September. The crater has changed beyond recognition after the major eruption of 4 September and the activity in the following days. It appears that there is now one single large pit-shaped crater in the western or northwestern part of the Voragine, with a depth of an estimated 200 m. A large intracrater cone has grown around this pit, and this is surrounded by a moat which separates it from the main rim of the Voragine. This intracrater cone is highest on the eastern side, presumably because fallout during the 4 September eruption was heaviest on that side. Much of the former "diaframma" between the Voragine and the adjacent Bocca Nuova has collapsed. Two rootless (fountain-fed) lava flows were emplaced on the ESE side of the Voragine during the 4 September eruption. The longer of the two flows is several hundred meters long while the smaller may be only 100-150 m long.
There was no activity within the Voragine during the first visits by Fulle, and the crater was also silent early on 26 September, but later that day, strong explosions occurred within the pit and dropped bombs onto the crater rims. However, Rivière had observed similar activity on 24 September, while Fulle was on the southeastern side of the summit area to see the ongoing effusive activity.
No significant activity has been observed since 22 September at the Bocca Nuova, and it appears that almost the whole crater floor is covered with lava of the 20 September eruptive episode. Rivière reported some kind of activity on 25 September, but its nature remains unknown. On the evening of 19 September, Rivière had been eyewitness of the onset of vigorous activity preceding the paroxysmal activity early the next day. He observed (and filmed) the sudden uplift of the entire crater floor and then escaped; there does not appear to have been any explosive activity at that time. Renewed explosive activity occurred at the Bocca Nuova on the evening of 21 September. Fulle reports that of the features of the former crater floor, only the northern rim of the southeastern cone is protruding through the20 September lava, and the vents in that cone themselves are covered with lava.
Rivière visited the Southeast Crater on 24 September and reported "lava" at a depth of about 20 m in that crater, but he saw no eruptive activity. The lava may thus be a solidified plug formed during the 4 September activity. Furthermore, a portion of the eastern crater rim has collapsed over a width of about 20-30 m; during a visit to the area by Boris Behncke (Dipartimento di Scienze Geologiche, University of Catania) on 22 September no eruptive activity was seen at the crater, but pulsating gas emissions came from the new collapse area.
Effusive activity continues from the new vents (first seen by Giuseppe Scarpinati on the morning of 11 September) near the 4 February eruptive fissure, but this activity is by no means continuous and experiences alternating surges and quiet periods. Lava flows have extended about 1 km downslope in that area and spilled down the western face of the Valle del Bove to an unknown elevation. In the next few days fieldwork will hopefully reveal more detail about the extent of new lava.
Interviews with people working at the tourist complex at Piano Provenzana, on the northern flank of Etna, have furnished interesting new details about the 4 September eruption of the Voragine. The event was well visible from there while the summit was veiled by dense clouds on all other sides. Photographs taken by a mountain guide from the area near Pizzi Deneri, at about 2600 m elevation on the northern flank, show an impressive lava fountain jetting to a height of more than 1500 m above the summit, dwarfing the prominent cone of the Northeast Crater which is visible at the base of the fountain. Such fountain heights have not been recorded at Etna before (about 600-700 m were reached by lava fountains from the Southeast Crater in September 1989), and this points to the magnitude of the 4 September event which was among the three most violent summit eruptions of the past 100 years (similar eruptions occurred on 17 July 1960, from the Voragine, and on 5 January 1990, from the Southeast Crater). It is hoped that field work during the next few days to weeks will render a comprehensive idea of this event, and that some of the photos made on the northern side of the volcano will be made available for this web site.

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Page set up on 27 May 1997, last modified on 5 October 1999