31 January 2003. Additional information and photos of 29 and 30 December 2002.
In the meantime, some interesting photos kindly submitted by Josef Fuchs, who was on Stromboli until 1 hour before the landslide, have become available to decadevolcano.net:

29 Dec., ca. 14h30 from the E rim of the Sciara del Fuoco at ca. 300 m elevation. Rockfalls and small landslides produce dense ashclouds that are similar to small pyroclastic flows.

29 December, ca. 21h00-21h30, from the path along the E rim of the Sciara del Fuoco at ca. 3-400 (?) m elevation. Two active lava flows are shown.

30 December, ca.12h15. View of the Sciara 1 hour before the landslide. Dust trails of small rockfalls and the cooled lava flows from 28 Dec. are visible.

Above photos copyright: Josef Fuchs.
Before using these photos elsewhere, please contact T. Pfeiffer or J. Fuchs.

16 January 2003: Photos of the ash cloud and the tsunami by an eyewitness on Stromboli

Philippe Guillemin (Montmorency, France) kindly provided the following extraordinary photographs. On Dec. 30, he was on the beach promenade close to the mole, waiting for the boat, when he and other observers were surprised by the tsunami waves that flooded the road. Just before, the ash-plume from behind the Sciara del Fuoco had appeared.

13h14. The huge ash-cloud that formed after the first landslide. Photo taken from the road at the beach close to San Vincenzo village (in middle ground).

13h15. The arrival of the first tsunami wave (ca. 2 m high at this location). Location is the same road, ca.400 m NE of mole at Scari.

13h16. The second wave of the first tsunami is retrieving, carrying floating debris and leaving a partially bathed person. Note the onset of a rain of scoria lapilli. 

Left: Although a bright sunny day, ash and mud create a surreal atmosphere. Taken from the square of St. Vincenzo at around 14h00.

Above photos copyright: Philippe Guillemin (2, Av. D. Leclerc, F-95160 Montmorency, France).
Before using these photos elsewhere, please contact T. Pfeiffer or P.Guillemin

16 January: The events from 28-30 December

Lava flow on Sciara del Fuoco (28 December 2002)
After a violent summit eruption on the evening of 28 December, a lava flow appeared from a fissure at the base of Stromboli's NE crater. The flow soon formed several tongues that traveled down the Sciara del Fuoco reaching the sea after ca. 30 minutes. It is yet  unclear how long lava emission did last. Early reports indicate that the effusive eruption was over after only 2 hrs already. No active flows were observed on a survey flight by INGV on 29 December. However, bad weather didn't allow good observations of the upper area and personal accounts from locals who climbed the mountain that day suggest that a small lava flow was still issuing from the crater on 29 Dec.

New flow and landslides (30 December 2002)
A new, smaller lava flow appeared following a possibly powerful eruption from the SE crater on the morning of 30 December. The vent of the new lava flow was located at ca. 550m a.s.l. and is still active by 16 January, emitting two small lava flows that reach the sea intermittently.

Landslides and tsunamis (30 Dec. 2002)
At 13:15 and 13:22 two major landslides formed on the Sciara del Fuoco. Their subaerial volumes have been estimated 600,000 m³ and ca. 5,000,000 m³, respectively.
Meanwhile, a recent bathymetric survey has confirmed that the landslides (at least the larger one) have affected a significant part of the submarine part of the Sciara del Fuoco as well. According to preliminary information, the affected area stretches until ca. 800 m b.s.l. This implies that the total volume of the slide be significantly larger, probably around 10 million cubic meters.
The landslides caused two tsunami waves that reached maximum heights of 5-10 m on the most exposed parts of Stromboli's coastline. A number of low-lying houses, other structures and boats were severely damaged (see photo gallery). 3 people were slightly injured, but as it seems only one as a direct hit by the wave, the other two because of panic.
Even in Milazzo, ca. 70 km away, the wave was clearly felt and strong enough to damage a moored oil tanker. 

Mud-rain
The landslides produced huge ash clouds that rain turned into mud. This mud formed a layer of purple-grey ash about 1 mm thick when observed dry on 31 Dec. It contained abundant accretionary lapilli and minor coarse fragments of black scoria, witnessing of the probably highly explosive onset of the lava emission the day before.

Lava flow on the Sciara del Fuoco on 31 Dec. 2002.

Images above: A newly formed delta as on 31 Dec. 2002. More photos available in the photo section.

Geologic significance of the 30 December landslide
It should be remembered, that the 30 December landslide is still 'small' - in geologic terms. Much larger ones have (and will) occur on Stromboli and many other places on the world. Landslides of various sizes are a common feature in all environments where extensive natural steep slopes occur. This is so much more the case where significant parts of the steep slope consist of unconsolidated material as in the case of the Sciara del Fuoco on Stromboli. The Sciara itself is merely the very recent (in geologic terms) filling of a depression left by a giant landslide (about 100-200 times bigger than the one on 30 Dec.) about 5000 years ago. Fortunately, the more catastrophic such a geologic event is, the more rare it is. As to the present situation on Stromboli, there is no indication that we might expect a really BIG landslide, i.e. failure of a whole island sector, in the near future.

An event like the one on 30 December does certainly not mean that Stromboli has suddenly become a more dangerous place. The risk for a landslide of the size experienced just recently had already been there before, but it was not in the public awareness and for some time, no such similar event has occurred. For the media, anything like this needs to be a catastrophic event. But the truth is, that the recent events on Stromboli were actually far from a natural desaster. It could have been much worse, if it had occurred in the summer season. But geologically spoken, this was nothing extremely exceptional. Probably in the time span of decades, such 'catastrophic' events (landslides, tsunamis, larger eruptions etc.) can actually be expected. It should have become clear, hence, that the risk from landslides and tsunamis has severely been underestimated and that this is a much more common hazard than believed. Finally, this is not only true for Stromboli, but any place with similar geologic backgrounds, especially volcanic islands.

Sources of primary information:
- Istituto Nazionale di Geofisica e Vulcanologia (I.N.G.V.) The official site of the volcanological research institute in Catania (in Italian) with frequent updates
- La Sicilia: The largest newspaper in Sicily (in Italian) usually reporting special events at their volcanoes...