Since December 28 2002 the Stromboli Volcano has been particularly active, causing more than once lava flows along its South Eastern slope called the ‘Sciara del Fuoco’ (the volcano is at its peak 3000 m high and approximately 2000 m of its surface is underwater).
The above mentioned slope is covered by loose material of motley dimensions (also made of metric blocks scattered in the sandy bottom matrix). The extreme inclination of the Sciara del Fuoco slope is the result of a major land slide event that occurred about 5000 years ago, following which the side of the volcanic cone was destroyed, leaving a significantly steep slope characterized by a critical incline particularly vulnerable to conditions of gravitational instability by the loose material it is made of. Therefore the triggering of land slides or land movement ranges from daily small slips of sandy material to the rolling of metric blocks up to potentially catastrophic events of major entity.
Conditions for the triggering of land slide phenomena are linked to the presence and scale of volcanic activity and in particular to the swelling of the volcanic edifice which may cause a sudden increase of the slope’s inclination level along the Sciara del Fuoco (i.e. consequent landslide phenomena), which can occur as quickly as in ten minutes particularly following powerful explosions or even slowly but progressively ( during charging phases of the deep magmatic system). Furthermore the critical stability conditions of the slope may degenerate as a result of an ongoing lava flow, which significantly increases the slope’s inclination and load.
In fact on December 30 2002, due to the critical volcanic activity of those days and the associated ongoing lava flow, a part of the Sciara del Fuoco collapsed causing a landslide of 18 million cubic meters of material. From the seismic wave recordings the detachment of the wall occurred in two separate close phases, in fact the landslide was first triggered in the submerged part of the Sciara and then spread to the surface part.
The underwater landslide generated a sequence of tsunami waves that in a very short time interested the whole island of Stromboli, the Northern part of the Island of Panarea and eventually spread to the other Islands of the Eolian Archipelago, along the Messina and Calabria coasts.
The maximum height reached by the tsunami wave on the coast, reported during the monitoring phase, reached peaks above 10m in many parts of the Island of Stromboli.