The 2002 Stromboli tsunami was caused by a volcanic eruption in the Aeolian Islands of Sicily, located on the Tyrrhenian Sea. In May 2002, one of the island's two active volcanoes, Stromboli, entered a new phase of explosive activity, initially characterized by gas and ash emissions from the summit craters. On 30 December 2002, the seismic network recorded two large collapses of a huge portion of the Sciara del Fuoco, which resulted in tsunamis. The first landslide occurred at 13:15, and the second around 13:23; both lasted 5–7 minutes. The event caused damage on the eastern coast of Stromboli and Panarea. These tsunamis have been considered the most violent ones to have struck Stromboli in the past 100 years.
History
Significant phenomena affected Stromboli during its fifth life cycle between 13,000 and 4000 BP (Neostromboli). After the major eruptive phase ended about 7500–7000 years ago, the volcano was affected by massive collapses, until it reached its maximum expansion in the northern sector, a period which lasted 3000 years. These were the most recent landslides, which led to the formation of the Sciara del Fuoco, a steep slope formed by lava, lapillus, and incandescent waste, which descends from the crater of Stromboli ( above sea level) to the sea.
Starting in May 2002, Stromboli was characterized by explosive activity at 100m above the summit craters. In November, the level of the lava in the craters was very high, resulting in an overflow in the upper part of the Sciara del Fuoco, which increased Strombolian activity and caused several explosions in early December. The heights of ejecta were intense at Crater 1. Afterwards, it reached above Crater 1, and the explosions left magma close to the crater's rim. At local time 18.30 (UTC+1) on 28 December, an unusual activity characterized by a long eruptive break occurred, causing the break of the northern wall of Crater 1, displacing part of the Sciara del Fuoco wall. The lava flows were steep: two came out from the base, and one from the middle of the break. It covered a unstable surface. The first flow reached the sea, which was about away, in 30 minutes. Significant volcanic activity changes did not occur, but a volcanic tremor started to increase. 12 hours later, two new gaps opened at about high, causing the start of two lava flows.
In the morning of 29 December, the lava flows along the Sciara del Fuoco were no longer fueled and two horizontal cracks opened on the surface, which was evidence of the continuous failure. On 30 December, the two gaps at 500 m and 600 m were being fueled once more, so lava flows started again. These flows went along the 28 December cracks while cutting through them. There was only ash emission, but it was not provoked by explosive activity—it was caused by frictional sliding. This revealed the concept of their formation, which began at 500 m at the eastern wall of the Sciara del Fuoco and continued down the slope. 20 minutes later, new breaks opened on the west side at about 500 m, which defined the border of the upcoming landslides that formed a few hours later. The gaps were filled with a mass of rock, probably because of the differences in the rocks in the middle, which caused the two rock's part failure that provoked two different landslides. The first part crashed into the sea at 13:14:05 and the second one at 13:22:38. These caused two tsunamis that struck Panarea Island, which is away from Stromboli. They took 6–7 minutes to reach it, and it was visible for 10 seconds. That was the first time a tsunami had been recorded on the island. Many minor landslides and collapses occurred, resulting in 6–8 Hz frequency content.
Causes On 30 December 2002, a part of the Sciara del Fuoco collapsed, causing a land movement of 18 million cubic meters of material. The wall detachment occurred in two phases: first, the landslide occurred in the submerged part of the Sciara del Fuoco, and later it spread to the surface.
The north-west side of the island is the result of the filling by the products of volcanic activity; a depression created as a result of multiple collapses of the same side occurred, according to recent studies. The landslides that produced the waves resulted from a sequence of deep movements (up to 70 m) involving the northeast sector of the subaerial and submarine side of the Sciara after the beginning of the volcanic eruptions on 28 December. The complex evolution that led to the destructive landslides of 30 December 2002 was reconstructed by group of researchers from the Sapienza University of Rome, the University of Bologna, the INGV-Section of Catania, and the Institute of Environmental Geology and Geoengineering of the CNR in a special study aimed at assessing the evolution of the stability conditions on behalf of the Civil Protection Department, following the strong changes in morphological conditions produced by the intense erosive and effusive activity of Stromboli. A decisive contribution to the analysis of the phenomena came from the work carried out by the research group members in the months before the events. They were involved in two projects of the National Volcanology Group, in which detailed surveys of the morphology of emerged and submerged slopes and studies on the stability of the slopes were carried out. These surveys were compared with those carried out in the days following the landslides of 30 December and integrated with the analysis of aerial photos following the landslide and with helicopter photos acquired during the sequence of the various phenomena of instability that followed the eruption. These data were used to analyse the backward stability of the slope that gave the first clues about the triggering mechanisms. Thus, it was possible to reconstruct the dynamics of the events. This reconstruction highlighted the fundamental role of the magma intrusion on the slope during the types of volcanic eruptions, which triggered the first deep movements of the north-east sector of the Sciara slope at least one day before the destructive landslide events, and of the instability of the submarine portion of the slope, from which the subsequent landslides propagated upstream.
Timing The seismograms recorded by the seismic stations installed in Stromboli and in Panarea provide time values that fit the scientific standards and are therefore of high reliability. Equally reliable is the time read in the sea level, recorded by the tide-gauge installed in the port of Panarea. From sources recorded by the seismic stations, it is evident that the two main landslides detached at 13:15 and at 13:22–13:23 local time and that the tsunamis hit north Panarea around 13:20 and 13:27, arriving at the Panarea harbor between 13:19 and 13:24.
Economic and cultural impact Stromboli is an active volcano whose persistent activity is considered mid-intensity explosive, occurring every 10 to 20 minutes. The presence of an active volcano in the Aeolian Islands attracts many people to visit the islands. Instead of discouraging tourists, the powerful activity of the volcano has attracted people to witness spectacular volcanic explosions and has increased the Island's economy. To manage and balance safety with the tourism-based economy, Stromboli has developed a safety guide for hiking trails and a handbook full of information related to the island, to behave in the best way during emergency situations. The greatest danger of the Stromboli eruptions is linked to the risk of tsunamis and the unpredictability of volcanic activity, which, although classified as "low-energy", is uninterrupted and can trigger devastating events.
Aftermath
Results On 30 December, two days after the start of the effusion phase, there was a partial collapse of one side of the volcano involved in the lava flow. The landslide event also affected submarine portions of the Sciara del Fuoco and caused a tidal wave whose maximum height was simulated around 10 m, the well-known tsunami of December 2002. The eruption lasted until the end of March, with small variations in the flow rate of lava and the positions of the eruptive mouths, with reduced or no explosive activity in the craters. Between the end of March and the beginning of April, the flow rate of the fluxes showed a significant decrease, and weak signals associated with small ash explosions observed in the crater area began to be recorded. On 5 April, at 8:12 AM (local time), a strong explosion occurred at the north-east crater. The explosion was followed by the expulsion of lava with the formation of a volcanic cloud characterized by a mushroom shape that reached a height of about 1150 m. The expelled products fell on the flanks of the volcano up to low altitude, causing fires in the vegetation. The effusive activity fed by the mouths, present in the lava field, set at an altitude of 600 m above sea level, continued accompanied by modest explosive activity at the craters, with sporadic explosive episodes of greater energy. Between June and the second half of July, there was a progressive decrease in the flow of lava and a gradual increase in explosive activity. On 21 July, the effusive activity was exhausted while the explosive activity started to involve all the craters in the summit area and had the typical characteristics of Strombolian activity with the launch of slag and lapilli. At the beginning of August, the magma was very superficial and the explosions were still low-energy. During the following months, the explosive activity resumed the typical characteristics of normal Strombolian volcanic activity. The first result which was caused by the volcano was an impressive scar which was 800 m deep, whereas on the coast the scar was over 40 m deep. Once the event occurred, the submarine morphology started to evolve quickly due to lava emission and rockfall from the subaerial slope. The development has been rapidly documented by a series of multibeam surveys. Firstly, an estimate of the rock volume involved in the submarine landslide shows that it might have been the origin of the tsunami. One of the reasons for the instability of Sciara del Fuoco is due to the submarine landslide.
Damages
On the island of Stromboli, the 2002 eruption caused two tsunamis: first, it caused the sea to recede and then provoked two anomalous waves of 20 meters that caused major damage in the Strombolian inhabited area called Ginostra, hitting the whole village. The event also forced the Civil Protection to close the island to tourists until an efficient alarm system against similar phenomena had been tested. No evacuation orders have ever been issued, although most residents preferred to spend the last night of 2002 in a safer environment on the island of Lipari.
The tsunami swept away boats, damaged houses along the coast, and injured six people, who were evacuated by helicopter and brought to two hospitals in Sicily. A tanker was seriously hit by the wave, causing an oil spill. Other minor effects of the giant wave were recorded in the confining Aeolian islands, especially in Panarea. The total damage to the infrastructures of Stromboli, Panarea, and Ginostra was worth €600,000.
Casualties and first aid
On 30 December 2002, a large amount of rock fell into the sea, causing an anomalous wave; because of it, three people were injured, and two people were transferred to hospitals in Messina. The first one resulted in a fractured leg, the second one a fractured foot, whereas the third injured person was a German citizen who had a slight head cut. Part of the island of Stromboli was evacuated: 100 people were transferred by Civil Protection helicopters to Messina and 40 to Lipari. Two helicopters from the Air Force took part in rescue operations after the event. Since the tsunami occurred in late December, the island was not filled with tourists, and reports of casualties indicate no deaths.
National emergency plan history