Italy's Volcanoes: The Cradle of Volcanology

Etna Decade Volcano, Italy
Eruption update:
20-31 July 2003
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ETNA IS NOT ERUPTING BUT RESTLESS

Fuming 2002 crater, Northeast Rift, July 2003
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

NOTE: The restrictions to excursions to Etna's summit area have been significantly modified. Free access is now allowed to up to 2500 m elevation (south flank) and 2600 m (north flank), four-wheel-drive tours go up to 2900 m on the southern flank (to the place where there was once the Torre del Filosofo mountain hut, and close to the newly formed craters) and to about 2500 m on the northern flank (Piano Provenzana area and entire fissure of the 2002-2003 eruption). Guided excursions for groups of up to 10 persons may visit any spot on the mountain. Read more on the Etna Excursions page

The latest update is below this line

31 July 2003 update. There has been further seismicity in the eastern sector of Mount Etna in the past ten days, which culminated in a burst of four small earthquakes (magnitudes up to 2.6) on 30 July 2003 that affected an area between the villages of Milo and Zafferana on the eastern flank of the volcano. Earthquakes of similar magnitudes (basically ranging in magnitude from 2 to about 2.5) had occurred at a rate of about one every one or two days previously, but they were scattered over a broad area in the eastern sector of Etna. At the summit craters, vigorous degassing continues at the Northeast Crater, and some less intense degassing is occurring at the Bocca Nuova. There are no indications of true eruptive activity, but the volcano remains restless.

20 July 2003 update. Mount Etna does not seem all that much of an active volcano in these days, except for the (sometimes impressing) gas plume that is being emanated from the summit craters, among these mostly from the Northeast Crater. Yet the volcano continues to provide more or less gentle reminders that the current quiet period is only temporary, that magma is again accumulating below the mountain, and that new eruptive activity is probably only a few weeks to months away.
There are four craters at the summit of Etna, two of which have one single vent (the Northeast and Southeast Craters), while the Bocca Nuova and the Voragine have two vents, respectively. Of this total of six vents, three are currently obstructed, while the other three are showing more or less intense degassing. The presence of obstructed vents within the summit craters is not really a happy thing, because one day, the one or the other of them will reopen, and this process might be explosive to some degree. There are indications that the southeastern pit of the Bocca Nuova, obstructed since many months, is gradually reopening. Minor emissions of brownish ash from this pit were most recently noted on 18 July. No other eruptive activity has been observed at the volcano ever since the latest flank eruption ended on 28 January 2003.
But the volcano is restless indeed, and it is very likely that it is already preparing its next eruption. Seismic activity has never really ceased since late January 2003, and seems to have picked up somewhat in the past three to four weeks, culminating in an earthquake on the Pernicana Fault System on 17 July, which was perceived by many people on the northeastern flank of Etna. The magnitude of that earthquake was probably around 3 and its focal depth quite shallow, as is common at the Pernicana Fault System. A rapid field investigation carried out a few hours after the event revealed that there was no evident ground fracturing in the areas affected by significant ground fracturing and deformation during previous earthquakes in the same area. However, repeated surveys of the Pernicana Fault System in many locations between about 1800 m elevation (Northeast Rift) and the Ionian coast (to the north of Giarre) through mid-July show that displacement along this fault system has never ceased since the dramatic slip of Etna's eastern flank at the beginning of the 2002-2003 eruption (a publication dealing with this subject, written by Neri, Acocella and Behncke, will likely appear in the Bulletin of Volcanology later this year). The Pernicana Fault System is nothing else but the northern boundary of a large portion of Etna's flank that is slowly sliding towards the Ionian Sea, a process that seems to be common at basaltic volcanoes and is also observed, even on a larger scale, at Kilauea volcano (Hawaii). Slippage of the unstable eastern flank of Etna is often associated with flank eruptions, which was dramatically manifested in October-November 2002. The fact that movement of the unstable flank is continuing is not reassuring.
So this is why we return to the good old question "when will there be the next eruption of Etna?" And the answer is, as always, that no one really knows. There is a lot of betting among geologists working on Etna in these times, and most bets are in favor of a new eruption before the end of 2003. Besides that, it is quite logical to assume that the volcano is recharging at more or less the same rate as it has done after the 2001 eruption, because there is simply no reason to believe that much has changed in the magma supply rate with the latest eruption. True enough, the 2002-2003 eruption produced about twice as much of magma as the 2001 eruption, but this does not necessarily hold any clue regarding the length of the ensuing repose period. It is more likely that the volume of a flank eruption depends on a very subtle interplay between the quantity of available magma and the degree of instability of the volcanic edifice. And currently, the edifice is more unstable than at any time during the past decade.
A quite sensible question concerns the character of the next eruption. Will it be as explosive as the previous one, will it once more produce enormous quantities of ash and thus render life, traffic and business in the densely populated Etna region difficult? This will be in part determined by the "new" magma source below the southern flank of the volcano, which yielded most of the eruptive products in both the 2001 and 2002-2003 eruptions. If this source continues to produce magma, the next eruption will probably be quite explosive, although explosivity is also strongly related to phreatomagmatism, i.e. interaction of magma with subsurface or surface water. In fact, much of the ash-producing activity in 2001 and 2002-2003 was phreatomagmatic. Phreatomagmatism can be expected if the vents of a future eruption once more open in the area once called "Piano del Lago", the Plain of the Lake, located between 2500 and 2900 m on the southern flank. The name is no longer justified, for the area is now dotted with three large pyroclastic cones that grew during the 2001 and 2002-2003 eruptions, and if another explosive eruption occurs there it will become a true mountain range.
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

Piano Provenzana - a requiem



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