28 February 1999

The effusive activity from the 4 February fissure is continuing without significant changes. During visits to the eruption site by Marco Fulle (on 24 February) and by Giuseppe Scarpinati (on 27 February), lava outflow was similar to that observed on 6 and 15 February, with an effusion rate of about 5 cubic meters per second. Scarpinati observed gas emission at high pressure from the cluster of hornitos in the upper part of the fissure, and mild explosive activity that built ever more hornitos. The activity, which is continuing in its fourth week, is attracting scores of tourists and television crews.

23 February 1999

While bad weather has hampered continuous observation of Etna's summit area today, last night the effusive activity from the 4 February eruptive fissure was well visible from Catania and other locations in eastern Sicily. For the second consecutive day, two active lava flows about 150 m apart were seen spilling down the steep western side of Valle del Bove, the more northerly flow being shorter than the southern flow. There appears to have been increased surface activity at the fissure where most lava flows had roofed over during the past few days, possibly a blockage of a lava tube forced lava to the surface.

22 February 1999

More news services with footage of the effusive activity have spread the false news of eruptive activity on the northeastern side of Etna (this time it's CNN), and while the footage is spectacular there as well, THERE IS NO ACTIVITY ON ETNA'S NE SIDE. However, lava continues to issue from the fissure southeast of the SE Cone, but there are no significant changes to the activity. Weather conditions are poor, there is very strong wind in the summit area, and any approach beyond the Montagnola is close to impossible.

21 February 1999

Spectacular video footage of Etna's ongoing eruption from the eruptive fissure on the southeastern base of the SE Cone has been shown in international television news during the past few days (see one example at BBC with beautiful photos and a movie clip that shows a situation very similar to that seen by us on Monday 15 February). Apparently some of these news services mentioned lava flows "from a crack on the northeast side" of the volcano, as well as a high probability that Etna is building for a major eruption. There are two false informations here. First, the crack is on the southeastern side, and there is absolutely no activity on the northeastern side. Second, there are no indications that Etna will produce a major eruption in the near future. However, it is true that lava continues to flow from the eruptive fissure into the Valle del Bove: yesterday evening a new surface flow began to spill down the steep western side of the Valle del Bove, and the flow front is slightly below 2000 m elevation, near the Monti Centenari, a cluster of cinder cones that formed during an eruption in 1852-1853.

19 February 1999

Effusive activity from the eruptive fissure on the southeastern base of the SE Cone continues into its third week. Last night, following an outbreak from a blocked lava tube above the rim of Valle del Bove, a brightly incandescent lava lobe flowed down into the Valle on top of earlier flows, possibly extending to its floor at about 2000 m elevation. There has been no further notable seismic activity at the volcano after the swarm of small earthquakes on the afternoon of 16 February.

17 February 1999

While the eruptive fissure on the southeastern base of the SE Cone continues to emit lava into the Valle del Bove, an earthquake swarm has occurred on the south-southeastern flank of the volcano yesterday, with epicenters scattered in the area of Pedara-Salto del Cane. The area has been among those most seismically active sectors of Etna in the past two years, and has numerous cinder cones from historic and prehistoric flank eruptions. At the same time it is one of the most densely populated sectors of the volcano. However, the hypocenters of yesterday's earthquakes were reportedly at a depth of around 9 km, and by yesterday evening seismic activity abated. A migration of earthquake hypocenters towards the surface would be a cause of considerable alarm, but no such migration has been observed so far, and yesterday's seismicity should be considered a relatively normal affair on an active volcano where numerous similar events have occurred in the past without being followed by any dramatic eruptive activity.

Careful analysis of my photos taken during the paroxysmal eruptive episode at the SE Cone on 4 February has revealed that the currently active fissure began to erupt while the paroxysmal activity from the new vent on the flank of the cone was still in its culminating phase. Photos taken at around 1745 h that day show that lava had already advanced several hundred meters towards southeast but was still far from the rim of Valle del Bove.

Etna seen from Catania on the evening of 13 February 1999. The lava flow that issues from the new eruptive fissure and spills down into Valle del Bove is clearly visible.

16 February 1999

On 15 February, Boris Behncke (IGGUC) and Giuseppe Scarpinati (delegate of the Paris-based Association Volcanologique Européenne) visited the eruptive fissure on the southeastern base of the SE Cone and observed its activity for about 4 hours. The fissure that opened during a late stage of the 4 February eruptive episode of the SE Cone has remained in continuous and vigorous effusive activity since then, and lava is spilling into the Valle del Bove, reaching about 2000 m elevation. There is no sign that the activity is diminishing, and the effusion rate remains at several cubic meters per second, maybe up to 5 cubic meters per second.
Lava continues to issue from a number of effusive vents on the active fissure, forming at least two main rivers and several smaller and short-lived flows. In the course of a few hours we saw some of the lesser flows cease and others reactivate, forming blocky a'a while the more vigorous and long-lived flows moved in well-defined channels and showed no significant variations in their flux. Numerous short lava tubes, well-developed flow channels and secondary vents had formed. Most effusive activity occurred in an area about 50-100 m downslope from the upper end of the fissure, but several vents were also higher upslope. In the uppermost part of the fissure, numerous hornitos had formed, most of them concentrated in three clusters, and this area had countless incandescent vents producing high-pressure gas emission accompanied by a persistent hissing noise. The largest hornitos formed absurdly thin, vertical spires up to 3 m high while others were small humps a few tens of centimeters high. We saw little explosive activity, only one vent in the uppermost hornito cluster rarely ejected incandescent pyroclastics.
Mild intracrater activity appears to be continuing in Bocca Nuova. Weak incandescence has been visible last night over the northwestern vents of that crater; no incandescence had been visible for several nights. Weak glow has also been visible at the summit of the SE Cone last night, indicating that mild activity may be occurring deep in the crater.

A magnitude 4.5 earthquake shook the northeastern part of Sicily shortly after noon on 14 February, causing slight damage in towns in the Gulf of Patti and terrorizing thousands of people in a vast area extending from the Aeolian Islands over Milazzo to Catania and as far as Siracusa. This earthquake was of tectonic origin, and its epicenter lay off the NNE coast of Sicily, on the "Tindari-Giardini" fault which extends from Lipari and Vulcano across the Nebrodi Mountains to the area northeast of Etna. The same fault produced a much stronger earthquake in April 1978 that caused significant ground fracturing on Vulcano and was followed by an increase of the fumarolic activity at that volcano (see the Vulcano pages for more information). According to a recently proposed hypothesis, volcanism on Lipari, Vulcano, and possibly Etna, may be related to oblique extension along parts of this fault, but any relationship between the 14 February earthquake and the activity of these volcanoes is excluded.

12 February 1999

The eruptive fissure on the southeastern base of the SE Cone has now been in eruption for more than one week, and there are no signs that the activity is ending. Unfortunately little observation of the activity and the dimensions of the new lava flow-field has been possible due to poor weather since early this week, but occasional glimpses through gaps in the cloud have permitted views of the dark lava field contrasting against the fresh snow that has fallen abundantly in the past few days. Tonight much of the cloud cover has dissipated, and the flowing lava is visible from Catania and numerous other locations, appearing as a bright red streak on the flank of the mountain. The lava field now appears to have enlarged laterally, while the lava fronts extend no more than 2 km from the eruptive fissure, and it is probable that the lava field is composed of numerous small lava lobes overriding each other. The latest eyewitness report of incandescent lava that I know of is from early this morning. Dense vapor plumes are being emitted from the summit craters, caused by humid and cool air rather than by increased eruptive activity, but it is probable that some activity is occurring on the floor of Bocca Nuova. No eruptive activity has been observed at the summit vent of the SE cone since the eruptive episode of 4 February.

10 February 1999

Activity from the eruptive fissure on the southeastern base of the SE Cone continues through its sixth day and shows no signs of abating. The lava flow in Valle del Bove has lengthened little, but the flow field is seen to be widening near the western rim of the Valle. There are no signs of significant activity elsewhere in the summit area, but it is probable that deep intracrater activity continues in Bocca Nuova which had shown increased activity just before the latest paroxysmal eruptive episode from the SE Cone on 4 February and the beginning of the ongoing fissure eruption. Weather conditions in these days are unstable, and observation of the volcano is thus difficult.

7 February 1999

The eruption from the new eruptive fracture at the southeastern base of the SE Cone is continuing, three days after its beginning, and lava is spilling down the steep western slope of Valle del Bove, extending down to an elevation of about 2500 m, but the flow front is advancing only very slowly. News about a second fracture on the northeastern flank of the cone must be corrected; field evidence shows that on that side lava simply overflowed from the summit vent of the cone through the deep notch in the crater rim already observed during a 21 January visit.
Yesterday (6 February) Boris Behncke (IGGUC) and Giuseppe Scarpinati (correspondent of L'Association Volcanologique Européenne and resident at Acireale) visited the new eruptive site to examine the activity, the extent of the lava flows erupted since 4 February, and the effects of the violent 4 February eruptive episode.
During the 4 February episode, the southeastern side of the SE Cone fractured from the summit down to its base, and the main vent of that activity formed about halfway down the cone's flank, erupting lava over the terrain below. A fracture extended still further downslope right to the base of the cone, and new vent progressively opened at lower elevations. It appears that the fracture at the base of the SE Cone formed only after the paroxysmal activity from the main vent on the cone's flank had waned, but there is little means to establish precisely the sequence of events. As viewed from Catania on 4 February, the lower vents became visible only about 30 minutes after the main activity had ceased, thanks to the fading light at dusk, but they may have been active before, when the area was still veiled behind a dense pall of ash and steam.
The new fracture lies in exact corrispondence with one of the two major fracture systems that extend southeast and northeast from the SE Cone, and have been the site of numerous flank eruptions in the past 50 years. The active zone extends over a length of little more than 100 m and consists of several vents that emit lava and display weak spattering. Vigorously fuming vents further uphill had evidently been active earlier but had ceased erupting. The main activity occurred from five vents around which small hornitos were building (one was observed to grow at least 0.5 m in less than one hour), and from these vents three main lava rivers extende southeastwards while minor ephemeral flows advanced only a few meters to a few tens of meters. One hornito emitted a sluggish flow that extended only a few meters downslope while another vent some 5 m below fed a vigorous flow that moved in a well defined flow channel with vertical walls 1.5 m high. The lowermost vent on the fissure emitted a broad (about 4 m-wide) flow that, after some 20 m, vanished in a tube to reappear at the surface some 15 m further downslope. Mild explosive activity at the source vent built a horseshore-shaped rim around the vent in about one hour; the fact that no such feature was there when we arrived at the site indicated that the vent had opened shortly before while others nearby had become extinct. The lava extending from where it reappeared flowed through a well-defined channel about 2.5-3 m wide which was surrounded by a small field of very smooth pahoehoe (a rare lava type at Etna), and moved at a speed of 1-2 m per second.
The output of all vents was roughly estimated at 5 cubic meters per second, an order of magnitude higher than the mean output of the SE Cone between July 1997 and July 1998.
The new lava flow-field extended southeastward and east-southeastward towards the rim of Valle del Bove. During the observation period at least two active branches of lava spilled over the rim of the Valle to extend a few hundred meters downslope.
There was no indication of eruptive activity at the summit vent of the SE Cone. A dense gas plume from Bocca Nuova (seen by Scarpinati in activity on the evening before the summit visit) was driven southward by a strong NNW wind while a second dense gas plume issued from NE Crater and was driven southeastwards.During the stay at the active fissure near the SE Cone, no noises except strong hissing noises at the degassing vents was heard.
There were signs that the activity at the higher vents was gradually weakening to become concentrated in the lower part of the fissure, but no evidence of new vents opening at lower elevation was found. This fact is not as trivial as it may seem. For the moment it appears as though some kind of persistent activity has established at the new eruptive fissure, and there will probably no more paroxysmal eruptive episodes at the SE Cone unless this activity ceases. That means, the main focus of activity has shifted from the SE Cone to the new fissure. It has been clear for some time that the eruptive dynamics of the SE Cone had changed since last summer, although there has been only a slight increase in its output, and therefore this change does not seem to be due to significantly increased magma ascent. Instead, it may be seen as an effect of the dramatically increased height of the cone since the summer of 1997, forcing magma to rise to ever higher elevations. This has not only caused the change from virtually continuous "persistent" activity (between November 1996 and late July 1998) to the frequent, brief, and violent eruptive episodes since mid-September 1998, but further growth of the cone at an amazing rate. At the onset of the 4 February eruptive episode, the hydrostatic pressure of the magma which was beginning to degas, to decompress and thus to expand, like in the previous episodes, grew beyond the threshhold of the cone, leading to its fracturing along a line of structural weakness. Evidently the fracturing did not proceed downslope from the summit of the cone, but rather in the manner of a vertical dike departing from the conduit of the SE Cone at some depth, otherwise it would not have followed so strictly the trend of the long-established southeastern fracture system.
It is likely that magma is supplied to the new fissure at the same rate at which it has previously been fed into the conduit of the SE Cone. The new vents, however, lie at an elevation to which the magma may rise much more easily than to the summit of the cone which lies at least 250 m higher. If this is true, the activity at the new fissure may last for quite some time, similar to the effusive activity from vents away from the NE Crater in the 1970's, and it should be considered a continuation of the persistent summit activity rather than some kind of lateral eruption.
However, the fact that the lateral southeastern fracture system (site of the most recent flank eruption in 1991-1993) has been reactivated - even though only in its uppermost part - casts a shadow of uncertainty on these assumptions. In the past 20 years or so, each time activity migrated from the SE Cone into the northeastern and/or southeastern fracture system, this marked the beginning of the propagation of activity towards lower elevations on the flanks, such as in 1978, 1979, 1986, 1989, and 1991. It can therefore not be excluded that the activity from the newly opened fracture may be an expression of increased structural instability, and thus a possible forerunner of eruption from vents at lower elevations. The fact that the activity is currently restricted only to the southeastern fracture system, and that it is continuing quietly for the third consecutive day may nonetheless signal that this time the situation is completely different from that of those earlier cases.
Local newspapers today report a rush of tourists to the eruption area, but actually only very few people were seen to make it through the strong wind and the choking, ground-hugging gas plume creeping across the access paths. We observed crowds of excursionists attempting to scale the snow-covered slope above the upper cable car station, many of them equipped with light shoes and inappropriate clothing, and almost nobody made it further than the "Piano del Lago", a flat area to the north of the Montagnola. Nonetheless the continued activity, the view of the incandescent lava flows at night from many locations in eastern Sicily and extensive mass media coverage are arousing interest and curiosity among the local population. Certainly nobody feels any fear, first because the lava flow is far from inhabited ares and will not extend far beyond its present dimensions, and second, because the attitude of the Etnean people towards their "muntagna" is generally very relaxed.

5 February 1999

After yesterday's spectacular eruptive episode from the SE Cone, more detail is emerging about the character of this event which may signal a change in the eruptive dynamics of that cone. At the height of the activity, shortly after 1630, a new large vent burst open about halfway down the SE flank of the cone; near simultaneously an eruptive fracture formed on the NE side of the cone. The new southeastern vent immediately emitted a huge jet of incandescent lava, and a lava flow rapidly spilled southeastwards from the vent. Less detail is known about the activity of the northeastern fissure, but it is clear that lava was produced also there, forming a flow that advanced towards Valle del Leone. As lava fountaining subsided, lava emission persisted at both sides of the SE Cone, with more than one vent producing very mild explosive activity on the southeastern side. After 1800, there was no longer any appreciable explosive activity, but lava continued to flow from both fractures through at least 2100 (as confirmed by the telescopic observations from Acireale by Giuseppe Scarpinati). None of the flows appears to have extended beyond the crest of Valle del Bove, and they are thus of similar length as other flows erupted recently from the SE Cone. Observation from Catania after 2300 revealed that incandescence was no longer visible on the southeastern side, but this morning (5 February) some fuming is visible at the site of the southeastern fracture.
The event left significant marks at the SE Cone which became evident this morning. The large main vent of yesterday is clearly visible on the southeastern side of the cone, and a fissure extends right up to the summit of the cone; a broader fissure is visible on the lower southeastern flank, below the main vent. The southeastern lava flow is a narrow black streak contrasting against the snow, and appears to have stopped just short of the crest of Valle del Bove. Although the new vents are very close to the Torre del Filosofo mountain hut, the structure does not appear to have suffered any damage because strong wind drove the fallout to the southwest. Giovanni Sturiale (IGGUC) who had driven up to the south side of Etna to view the event at closer range reported a fairly thick ash deposit on the southwestern side of the mountain at about 1000-1500 m elevation.
Information from Giuseppe Scarpinati in Acireale indicates that during the night preceding the latest episode, activity had been more intense than previously in Bocca Nuova, and at dawn yesterday, glow at this crater could be seen with the naked eye. Yesterday evening, no incandescence was visible at Bocca Nuova, but today there is intense and pulsating gas emission, indicating that eruptive activity in the crater is continuing.
Much can be speculated about the significance of yesterday's eruptive episode. This is the first time since 1993 that new vents (that is, other than those within the four summit craters - SE Crater, NE Crater, Bocca Nuova, and Voragine) have erupted. Furthermore, the fact that eruptive fractures have opened on both sides of the SE Cone in strict correspondence to the two main fracture systems extending northeast and southeast may indicate that after an unusally stable period, this area may have become more unstable, and this change may be very significant. In a very similar manner, the SE Cone produced a dramatic sequence of eruptive episodes in September 1989. Towards the end of the sequence, these events were accompanied by the opening of eruptive fractures on the northeastern and southeastern sides of the SE Cone, heralding the opening of eruptive fractures in Valle del Leone and the downslope extension of non-eruptive fractures on the southeastern flank. It is not clear to what degree the current events can be compared to the 1989 eruptions, but they merit heightened attention. For the moment the area of the SE Cone appears quiet again, but everyone here is expecting the next eruptive episode with apprehension and curiosity. Three-and-a-half years after the beginning of the current cycle of summit eruptions, the fascinating and extraordinarily variable pyrotechnic show is continuing, and it is promising to continue in this manner.

4 February 1999

UPDATE, 1830 h local time (GMT+1) - A new paroxysmal eruptive episode from SE Cone occurred between 1600 h and 17150 h, producing a spectacular eruption column that was well visible from Catania and all around the mountain. Like previous episodes, this event was characterized by vigorous fire-fountaining, tephra emission, and lava flows. Different from previous episodes, much of this activity appears to have come from a new vent that has opened at the south-southeastern base of the SE Cone. I observed the activity after about 1645 h from the Giardino Bellini, a fairly panoramic observation point in the center of Catania, and the main fountain appeared to originate from a point well below the summit of the SE Cone which was plainly visible behind the fountain. Furthermore, a broad lava flow was visible at the base of the fountain, extending to the southeast.
As the activity waned, the entire area around SE Cone remained veiled by dense steam clouds, indicating that some kind of activity was going on, even though tephra emission had ceased. As it got darker and darker, an incandescent spot became visible at the base of SE Cone, and observation with the zoom lens of my camera revealed that at least two or three incandescent spots aligned roughly NW-SE had formed at the base of the cone, possibly these were new vents aligned on a small eruptive fissure.
When returning to the Istituto di Geologia e Geofisica shortly before 1800, I noted that a fairly long lava flow extended from the new eruptive site to the ESE but had not yet begun to spill down into the Valle del Bove. At the time of writing, lava effusion from the new site is continuing, but the effusion rate appears to be relatively low - and it seems to be diminishing, too - and there is little evidence of any explosive activity at the new vent(s).
What has happened? There appears to be a correlation between the length of the repose periods between eruptive episodes from SE Cone, the height of this cone, and tonight's activity from the new vent (or vents) at its base. The cone has grown rapidly in the past five months, and this has certainly caused significant changes to the pressure regime in its conduit - the magma must now rise much higher than before, and the elevation of around 3300 m appears to be a critical factor to the dynamics of magma ascent in Etna's central conduit system.This, among others, may be a reason why the activity of the SE Cone changed from the continuous mild Strombolian and effusive activity (between November 1996 and July 1998) to the episodic behavior initiated in September 1998. After a series of six eruptive episodes occurring in rapid succession in January (on 5, 9-10, 13, 18, 20 and 23 January), the SE Cone remained unusually quiet for 13 days before becoming active again this afternoon. Evidently the hydrostatic pressure of the magma in the conduit was so high that it broke through the side of the cone.
The opening of new vents away from Etna's four summit craters - which have been the only sites of eruptive activity since the current cycle of summit eruptions began in July 1995 - may be significant because this means that the structural stability of the past four years may have been weakened. The SE Cone sits in a crucial location at the intersection of Etna's two most active eruptive fracture systems during the past 50 years, and it has participated in some manner in 11 of the 14 major flank eruptions during that period. Many of these eruptions have actually started with vigorous activity at the SE Crater (I prefer the naming "SE Cone" for the feature as it is now, but use "SE Crater" when discussing events prior to 1998). This was most impressive in September 1989 when the crater produced an awesome sequence of eruptive episodes, the latter half of which was accompanied by the opening of eruptive fractures on the flanks of the cone, before activity extended into the two fracture systems extending downslope from the crater, to produce a flank eruption in Valle del Leone, and a non-eruptive fracture on the SE flank that caused much apprehension.
On the other hand this new facet of Etna's pyrotechnical displays may be seen as strongly related to magma ascent in the central conduit system, with no influence on the lateral fracture system, as has occurred three times during the 1955-1971 summit eruptions. As this evening proceeds, the activity from the vent(s) at the base of the SE Cone appears to be gradually waning, but it will only show in the next few days whether Etna's activity has entered into a distinctly different phase, or if this is only a minor deviation from the behavior established in the past five months.

The following had been added to this page before, shortly after 1600 h., at the onset of the eruptive episode. - Nearly two weeks after the previous eruptive episode from the SE Cone (on the morning of 23 January), another eruptive episode has begun from the same vent this afternoon at around 1600 h (local time = GMT+1). During the intial phase, an intermittent lava fountain played from the summit crater of the cone, feeding a dilute eruption column. Intense continuous intracrater activity has occurred during the past few days in Bocca Nuova causing intermittent glows visible at night. During the past week, there have been frequent occasions when Bocca Nuova generated massive steam and gas plumes that rose up to 3 km above the summit (there is unusually little wind at the summit in these days).