QUIET DEGASSING AT THE SUMMIT CRATERS

This is the uppermost of the new craters formed on the Northeast Rift of Etna on 27 October 2002, at about 2500 m elevation. Steam is still issuing from this crater, indicating that the dike which fed the eruption is still hot. Fumarolic activity had been common in this area also before the eruption. Diameter of this crater is about 50 m. Photograph taken on 12 July 2003, view is to the south

The latest update is below this line

31 August 2003 update. No further eruptive activity has occurred at Mount Etna during the past three weeks, since its first reasonably serious attempt to return on the stage on 11 August. Quiet degassing has continued from the summit craters, among which the Northeast Crater is the most vigorous.
The fact that the 11 August activity was only an isolated, short-lived episode may have disillusioned hard-core volcano fans, but to people living around the volcano and to scientists it means a pleasant respite, following the frantic period of continuous summit eruptions (1995-2001) and the two destructive flank eruptions in 2001 and 2002-2003. And despite the current calm, the volcano may - it actually will - return to vigorous life all too soon.
Two further live-cams have been installed on the upper southern (Montagnola) and northern (Pizzi Deneri) flanks of Mount Etna by the staff of Etna Trekking, an organization of mountain guides based in the town of Linguaglossa. These webcams complement those of the Catania section of the Istituto Nazionale di Geofisica e Vulcanologia (INGV-CT), which look at Etna from Milo (eastern flank) and Catania (southern base of Etna). This is a fine initiative coming from a place that is still suffering the legacy of Etna's latest eruption, which virtually cancelled tourism business from this side of the volcano. Although jeep tours and other excursions are once more offered on the northern flank of Etna, there is hardly any reponse from tourists, tour operators and travel agencies, and at best a few dozen people per day come to take advantage of the existing opportunities. This is in stark contrast with the many thousand daily visitors on Etna's southern side where reconstruction work is in full swing, and even the cable car (severely damaged in 2001 and again in 2002-2003) is planned to be back in function in early 2004.

17 August 2003 update. The episode of explosive activity at the Northeast Crater of Mount Etna on 11 August 2003 seems to have been, for the moment, an isolated event of fairly small dimensions. A report sent to the Volcano Listserver by the Catania section of the Istituto Nazionale di Geofisica e Vulcanologia on 16 August 2003 gives further detail about the episode, which was accompanied by volcanic tremor and explosion quakes registered by the seismographs of the INGV monitoring network in the summit area; however, a visit to the summit on 14 August revealed no continuing explosive activity, and the seismicity had returned to background levels. Also on 14 August, Charles Rivière visited the Northeast Crater and noted a complete absence of explosive activity, and no products of recent magmatic activity were found on the crater rims.
Summit activity is often discontinuous and intermittent, and therefore it is likely that further eruptive activity will occur at Etna's summit in the near future.

12 August 2003 update. It seems like 11 August 2003 is a new date to remember in the history of Etna's eruptive activity. On the evening of that day, weak, fluctuating glows were observed at the base of the dense gas column which is issuing from the crater since many months. The observations were made from the town of Zafferana, on the southeastern side of the volcano, and kindly reported by Vittorio Zanon. Field observations will be made in the next few days to reveal if any fresh magmatic products have been ejected by the activity.
The Northeast Crater was observed on the previous day by Charles Rivière, who did not note any evident eruptive activity but strong degassing. However, Rivière reports audible detonations from the Northeast Crater on 5 and 6 August, but no visible eruptive activity is known to have occurred on those occasions. The date of the ascertained beginning of the new activity thus falls on 11 August, 195 days after the end of the latest flank eruption.
What does the resumption of summit activity mean?
Firstly, it means that magma has risen to the surface within the central conduit system of Etna (it is rather correct to speak of a "conduit system" because there are at least four conduits, corresponding to the number of summit craters). This is quite a normal process at what can be said to be the second most active volcano on Earth, which essentially is continuously active. Magma is drained from the central conduit system during lateral flank eruptions, but supply from an assumed upper mantle magma source is continuous, and thus the system begins to recharge immediately after the end of a flank eruption. The more magma has been lost during that eruption, the longer does the recharging process last. Following the very voluminous 1991-1993 flank eruption, this process lasted more than 2 years.
During the 2002-2003 eruption, a relatively small amount of magma (about ten million cubic meters ) was evacuated from the central conduit system. This was emitted on the northeastern flank of Etna during the first week of the eruption, and in spite of the great devastation caused by this lava, its volume amounts only to about 12 per cent of the total volume of the eruption. The remaining 88 per cent of the erupted magma did not come from the central conduit system, but from a separate (eccentric) reservoir, which is fed from the same magma source in the upper mantle but does not seem to be in any direct contact with the central conduit system.
The draining of magma from the central conduit system at the beginning of the 2002-2003 eruption ended on 5 November 2002, and it can be assumed that after that date the system immediately began recharging, even with the eccentric eruption on the southern flank continuing for another two-and-a-half months. The recharging has thus been under way for nine months. This is not all too dissimilar to the recharging period following the 2001 eruption, which lasted ten months.
Secondly, the new summit activity means that the newly rising magma has not bypassed the summit craters and produced a flank eruption, as had been feared by many, and the volcano is presumably unstable but not as unstable as to give way immediately to the rising magma and let it drain through its flanks. Yet there is absolutely no means to say, at this moment, when this will occur. It can only be hoped that the volcano will give more warning than the ridiculous two hours of seismicity prior to the beginning of the latest flank eruption. For the moment, there are two possibilities how the activity will develop in the next weeks to months: (a) it may continue at the summit and possibly involve also one or more of the other three summit craters (the Bocca Nuova seems the most likely candidate, for it has shown sympathetic activity with the Northeast Crater also at the end of the previous two repose periods, in 1995 and 2002). If the summit activity continues long enough, it might progressively increase and bring a return of beautiful lava fountains, which is surely the option wished by most people living and working on Etna; (b) flank instability may facilitate the draining of magma into the flanks (most likely in those areas already destabilized during the 2001 and 2002-2003 eruptions) and thus lead to a new lateral flank eruption in relatively short time.
It does not tell us anything about the state of the eccentric magma reservoir below the southern flank and its potential of producing more flank eruptions, whether it is recharging and if it is shifting - that reservoir does not depend directly on the processes within the central conduit system. However, the eccentric reservoir seems to have a strong influence on the stability of the Etnean volcanic edifice. Spreading and slippage of Etna's eastern flank is now suspected by many researchers to be largely facilitated by the accumulation of magma below the base of the volcanic edifice. And it was most probably a major slip of that flank which in turn facilitated the eruption of 2002-2003 - both lateral and eccentric.
Thirdly, the renewed summit activity simply means that Etna is back on the scene. It means that the period of calm is over, and it reminds everybody that the end of the 2002-2003 eruption was not the end of all things for Etna, but that it would give us only a temporary break.
If the July-September 2002 summit activity can be taken as a model of how the new activity will develop, then it is likely that it will go on with some fluctuations, sometimes being more vigorous and at other times absent. It will lead to a gradual filling of the great central pit of the Northeast Crater. In 2002 that pit was filled to within 50 m of its rim - see the nice photographic documentation of that activity by Charles Rivière (July-August 2002, and September-October 2002), the only existing on-line record of that brief eruptive period. The 2002 Northeast Crater activity lasted from late June until late September and ceased abruptly immediately after the first strong earthquake at the Pernicana Fault on 22 September, which marked the beginning of accelerated flank slip, and probably the first principal step leading to the flank eruption five weeks later.
If the summit activity extends also to the other craters, these might undergo a process of filling of their active pits as well. Presently, the only summit crater that has no inner pit is the Southeast Crater. If this crater resumes its activity, this may be violent and destroy the unstable summit of its cone, or gradual, with Strombolian bursts, and lava outflow possibly from one of its side vents that were established in 2000-2001.
To see how Etna looks like in these days, visit the new and growing photo gallery "Return to Etna, 2003". Many photographs taken during 14 years of visits to, and life near, Mount Etna are available in the Etna photo gallery.

A summary of the 2002-2003 eruption (revised early August 2003)

Piano Provenzana - a requiem

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