Updates March-April 1998
The most recent updates
Etna news archive
27 April 1998
SE Crater continues to erupt, with small Strombolian explosions from the central conelet and lava effusion onto the outer flanks of the SE Crater cone. Last night a flow descended on the southwestern flank but did not extend to the base of the cone. No activity has been observed directly at the other summit craters, but a colleague from the Istituto Internazionale di Vulcanologia said she heard explosion sounds that possibly came from Bocca Nuova while doing fieldwork on the mountain last week. As for the August 1997-March 1998 report to GVN on the activity of Etna, we are in the final phase of the preparation, and the report will be sent to GVN next week. In these days, I am scanning tens of slides taken on Etna during the past ten months which will soon appear on the Etna pages and render a graphic idea of what has happened at the volcano in this period.
7 April 1998
All four summit craters were visited yesterday in order to observe the activity of the craters and study the effects of the 27-28 March eruptive episode at NE Crater. Activity occurred only in the southwestern vent of the Voragine and at SE Crater.
NE CRATER AND THE EFFECTS OF THE 27-28 MARCH ERUPTION. The vigorous 90+ minutes episode of high lava fountaining from NE Crater on 27-28 March left a most peculiar deposit that appears to consist of a proximal and a distal facies while there is no medial facies. Centimeter-sized, highly inflated pumiceous scoriae were abundant a few hundred m south of the 1971 "Observatory Cone", and the deposit was near continuous on the western side of that cone, with maximum clast sizes exceeding 5 cm. Closer to the southwestern base of SE Crater, the deposit was no longer continuous, but clasts up to 10 cm in length were found. A few cm-sized clasts per square m were present on the southwestern flank of SE Crater, but near its southwestern and western rims any products from the NE Crater eruption were absent. No fresh pyroclastics were found on the southern, western and northern rims of Bocca Nuova.
Close to NE Crater, surprisingly little fallout of the eruption was found. Black dense bombs extended little beyond the base of the cone, and of the southwestern, western and southeastern flanks only the upper half to the upper third were covered with fresh bombs. A few impact craters were seen in the northern part of the Voragine crater floor while on the northern wall of that crater (which is poorly distinguishable from NE Crater's south flank) bombs had formed a near continuous cover. On the southern and southeastern rim of NE Craterm the deposit was at most a few meters thick as judged from exposures within gaping cracks which had opened as the deposit compacted and slid towards the deeper part of the crater. Sulfur deposits were abundant on the deposit in this area. Many circumferential fractures were present in the deposit around the central pit of NE Crater.
The inner terrace surrounding the central pit which before the eruption had stood some 5-10 m below the outer terrace had subsided by at least 10 m, exposing huge caverns in the vertical scarp along which subsidence took place, these were formed during the summer of 1996 when the crater was filled with lava which crusted over and later drained onto the outer flanks of the cone.
The dimensions of the central pit had changed little during the eruption, but its floor had risen to within about 50-60 m of the lowest point on the pit's rim. The floor was covered with huge blocks and smaller tephra and had a chaotic aspect. Weak vapor emission occurred from several holes and fractures, and one vent emitted a more consistent gas plume that rose high above the pit. There was no evidence of fresh ejecta around these vents indicating that no significant eruptive activity had taken place there since the 27-28 March eruption.
The preliminary study of the pyroclastic deposit allows a few conclusions:
Bombs ejected by the lava fountains mostly fell back onto the crater and in its immediate vicinity. Inflated pumiceous scoriae were carried to higher elevations by thermal convection and fell only at a certain distance from the erupting vent, about 1 km from NE Crater towards south. Since there was virtually no wind during the eruption, the dispersal may be similar in the other directions from the crater.
VORAGINE. Since the last visit to this crater on 10 February, a few minor morphologic changes have occurred in this crater. The most significant is the formation of a new crater less than 10 m in diameter on the western side of the central conelet. Some growth had occurred at the central conelet, and the surrounding crater floor was covered with finer-grained tephra. The southwestern vent which lies a the base of the septum between the Voragine and Bocca Nuova had enlarged and was now some 40 m in diameter. This vent was the only site of eruptive activity within the crater during the visit, large explosions occurred everey 3-5 minutes, ejecting bombs tens of meters high. Some bombs flew over the septum and fell into the Bocca Nuova.
BOCCA NUOVA. For the first time since I visit the summit regularly (that is, since June 1997), I saw this crater completely inactive. Wholesale collapse had occurred at the northern and southeastern eruptive areas. A vast collapse depression had formed at the former, leaving only the northern part of the large cone that had grown there until the end of 1997. Several steaming vents were present in the central part of this depression, but no eruptive activity was observed. The southeastern vents did not erupt as well, and there apears to have been considerable destruction of the cone at those vents, but dense gas clouds prevented good views.
SE CRATER. During the seven weeks since the previous visit (on 17 February), significant morphologic changes have occurred at this crater. The summit portion of the intracrater conelet collapsed or was destroyed by the vigorous explosive activity during the last week of March. The southeastern portion of the conelet stood about 20 m above the "Fortino", the highest point on the WNW rim of SE Crater, the western summit area of the conelet was about 10 m lower, and its southern crater rim had broken down, forming a series of subparallel ridges on the southern flank of the conelet. A depression had formed on the lower eastern flank of the conelet; this was the site of a new effusive vent formed only shortly (that is, hours to days) before.
The effusive vent area that had been active for many months in the southern and southeastern sectors of the conelet's flank was inactive; here the level of the intracrater lava field was only a few meters lower than the collapsed southern crater rim of the central conelet. Lava had buried the old rim of SE Crater on all sides except in the west and northwest where the old rim stood a few meters above the intracrater lava field. Lava had flowed recently around the western and northern sides of the central conelet and overflowed onto the northern outer flank of SE Crater, forming a short (less than 100 m) lobe. On the southwestern flank of SE Crater a long-lived lava flow had been active from mid-February until early March; this flow had extended as far as a similar flow emplaced in January, to near the western base of the 1971 "Observatory Cone". In the middle part of the southwestern slope of SE Crater, the flow had for the first time formed a small lobe on the western side of another cone formed in 1971, the "Western vent".
The new effusive vent on the eastern base of the intracrater conelet had apparently formed only shortly before the visit since the depression around it had not yet been completely filled. The extrusion of lava at this site had been preceded by subsidence at the eastern base of the conelet. Meter-sized slabs of older lava had been uplifted and tilted, and fresh lava was being squeezed up through cracks between these slabs, accompanied by high-pressure gas venting that produced a loud hissing noise. Several bulbuous lobes of smooth-surfaced lava oozed very slowly into the deepest part of the depression, forming "buds" in a manner strikingly similar to the mode in which pillow lava forms under water. A much more vigorous flow issued further to the east from a U-shaped vent, similar to ephemeral vents seen on other occasions at the base of the central conelet and within SE Crater. The flow velocity was about 0.3 m/s. Yet another flow began to issue during the observation period from below an upheaved slab of older lava which had spectacular lava stalagtites on its bottom side. These two flows soon formed distinct levees and bifurcated into several branches that advanced towards the northeastern part of the crater and spilled onto the northeastern flank of SE Crater, forming an active tongue that extended some 150 m downslope.
Explosive activity occurred from two vents within the crater of the central conelet, and like during visits in January and February, activity alternated between these vents but they never erupted simultaneously. Eruptions at one vent were very noisy while the other vent erupted rather silently; it was not possible to determine the precise locations of these vents with respect to each other. There were distinct cycles in the activity, beginning with weak activity that gradually increased to culminate in one or two powerful explosions which hurled meter-sized clots of brilliantly incandescent lava high into the air. Several cycles were particularly vigorous, with strong explosions following each other in rapid succession. Bombs from these explosions fell exclusively on the northern and northeastern flanks of the conelet. Lighter scoriae were observed to fall back onto the ground in a highly turbulent manner.
If activity continues at SE Crater like it did during the past year, even the remaining parts of the former crater rim will be buried by new lava, and the central conelet will eventually merge with the outer slopes of SE Crater. However, with the focus of the effusive activity having shifted to the eastern side of the crater, it will probably take months until lava will bury the western rim of SE Crater.
30 March 1998
The following is a preliminary summary of the events of the past weekend, and its content may prove insufficient or incorrect by ongoing research and analysis. I recommend to contact scientists at the Istituto Internazionale di Vulcanologia before using this information for further distribution. I will try to present more detailed and accurate information during the forthcoming days.
In one of the most spectacular eruptive events of the past few years, NE Crater produced an episode of paroxysmal lava fountaining during the night of 27-28 March. The event began shortly before midnight and lasted about two hours. Pyroclastics mainly fell back into the crater and over the area of nearby Voragine and Bocca Nuova. Activity following this event has been low with only SE Crater producing weak Strombolian eruptions.
PREMONITORY ACTIVITY. Volcanic tremor was registered by seismic stations in the summit area since the early morning of 27 March. At about 1000 (local time), NE Crater began to emit ash plumes; based on the seismic activity, this activity was interpreted as true magmatic activity, distinctly different from ash plumes generated by intracrater collapse. Ash emissions continued until shortly after 1600. By nightfall, sporadic ejections of incandescent bombs became visible in images transmitted by the Montagnola telecamera, some of them attaining heights of several hundred m above the crater. At the same time, SE Crater was intensely active, with vigorous and continuous Strombolian bursts from the intracrater cone, and a lava flow spilling down the southwestern flank of the SE Crater cone. The Strombolian ejections from NE Crater gradually increased in intensity and became virtually continuous by 2200.
PAROXYSMAL ACTIVITY. Shortly before midnight, the Strombolian ejections from NE Crater merged into a continuous, though pulsating, fountain with jets rising 300-350 m above the rim of the active vent, located within the collapse pit in the south-central part of the crater. Large bombs fell abundantly onto the lava platform surrounding the erupting pit and into the adjacent Voragine and Bocca Nuova craters. Occasional jets dropped bombs as far as the southern flank of the main summit cone and down to its base, more than 1 km south and southwest of the active vent. The activity produced loud detonations that were heard in a vast area mainly on the eastern and southeastern flanks where hundreds of thousands of residents and many tourists watched the display at a safe distance. By about 0130, the activity began to decline and was virtually over after 0200. Monitoring by the Montagnola telecamera showed no evidence of further eruptive activity at NE Crater while SE Crater continued to produce Strombolian explosions and a lava flow on its southwestern flank.
DEPOSITS. During a helicopter overflight on the morning of 28 March, IIV scientists noted surprisingly little deposit produced by the paroxysm of the previous night. The snow cover on the eastern and northern sides of the crater showed no evidence of any pyroclastic fall on these sides, and no significant tephra deposit was found around the crater. These observations suggest that no tephra-laden eruption column had formed during the paroxysmal activity, and virtually all fallout was ballistic, being limited to the southern and western sides of the crater. Evidently most bombs fell into the adjacent Voragine, and in lesser quantities in the Bocca Nuova. At NE Crater itself, the collapse pit (which was the locus of the activity) formed in October 1996 in the south-central part of the intracrater platform was filled to within about 20 m of its rim while the surrounding platform appears to have subsided by several meters.
POST-PAROXYSMAL ACTIVITY. During the day after the paroxysm, NE Crater emitted a few isolated ash plumes to several hundred m above the summit, but there was no clear evidence of renewed Strombolian activity. Moderate Strombolian activity continued at SE Crater, but effusive activity on the southwestern flank ceased sometime during 29 March, and it is not known if lava flows are occurring within the crater at this moment.
MEDIA COVERAGE OF THE ERUPTION. The NE Crater paroxysm of 27-28 March was widely reported in local news media and news spread over the globe during the following day. Sicilian newspapers presented headlines saying "This is finally the beginning of the expected big eruption"; these reports were accompanied by spectacular photos which, however, were taken at SE Crater in mid-January. Some reports stated that the paroxysm originated at both NE Crater and SE Crater simultaneously and both emitted lava flows (NE Crater did, however, not produce any lava flow). A reported "lava lake" within the active pit in NE Crater is actually the pyroclastic fill left by the paroxysmal fountaining which probably showed some incandescence many hours after the end of the event.
Internet news sources have some info about the event, mostly in Italian language. A spectacular video is available in VDO format at the Telecolor TV station, Catania (the VDO Live Player plug-in is required to view the video)
SIGNIFICANCE OF THE EVENT. In a preliminary evaluation, the 27-28 March NE Crater eruption appears to be but another episode of paroxysmal lava fountaining, similar to, although possibly more vigorous than, a series of paroxysmal eruptive episodes observed at the same crater between November 1995 and June 1996, and many times during the late 1970's and early 1980's. The volume of pyroclastics emitted in the most recent episode seems to be fairly small, and fieldwork in the next few days may reveal the true dimensions of the event as being not too exceptional. In the framework of Etna's recent and current activity, the event marks a resumption of more vigorous activity at NE Crater which has displayed only weak activity since August 1996, and further episodes of similar activity may occur in the near future. There is no clear evidence that this activity is a predecessor of a major flank eruption, and for the moment it is just another, though spectacular, episode of Etna's multifaceted summit eruption initiated in July 1995.
21 March 1998
A new lava flow began moving down the south-southwestern flank of SE Crater yesterday evening; a second lobe spilled down adjacent to this flow early today. These new flows are only a few hundred m long and are similar to flows emplaced on the flanks of SE Crater during recent months. Explosive activity at the intracrater cone is weak; there are no indications of significant activity in the other summit craters. Weather conditions continue to be unstable, with a new cold front due to arrive in the area during the next few days.
19 March 1998
SE Crater appears to be the only center of eruptive activity on Etna in the past few days, with weak Strombolian activity accompanied by occasional minor overflows of lava onto the flanks. Weather conditions have improved after about ten days of frequent snowfalls and clouds, but it appears that there is still no return to reasonably stable conditions.
11 March 1998
Lava continues to spill down the southeastern flank of SE Crater while sporadic night glow is visible at Bocca Nuova in these days. A cold front has brought much new snow to Etna and its surroundings, after a warm period during which much of the previously fallen snow on the mountain had melted.
5 March 1998
The summit eruption continues with lava effusion on the flanks of SE Crater (last night the flow direction shifted to the south-southeastern flank) and weak activity at Bocca Nuova. Since the activity is continuing in a relatively stable manner, updates to this page will only be provided once there are significant changes in the activity or after visits to the summit craters. About once per week there will be a summary of the recent activity provided the activity continues in a similar manner.
3 March 1998
Bocca Nuova and SE Crater continue to erupt, although the activity of the former appears to have decreased. At SE Crater, two lava flows were active last night on the southwestern and southeastern flanks, the latter being the more vigorous of these flows. The situation continues to be relatively stable. Weather conditions are variable today, but the forecasts for the next few days are relatively good.