Logo
  • Stampa

March 1981 - The eruption that narrowly missed the town of Randazzo

Randazzo_1998_09_30_730

Remains of the formerly stately land house "Casa Scala", one of the numerous buildings destroyed by the main lava flow of the March 1981 eruption near the town of Randazzo. Photo by Boris Behncke, INGV-CT

17 March 1981: in the past five weeks, about 4000 B-type seismic events of low magnitude were recorded by the seismic network in the summit area of Etna and the north flank of the volcano. An intense seismic crisis has started on 16 March with more than 50 events per hour, mainly characterized by shallow earthquakes, with the weakest and most superficial localized near what will soon become the theater of a new eruption. Early on 17 March, it is feared that this is the prelude for a new flank eruption in this sector of the volcano, less than 2 years after its latest lateral eruption that affected the eastern flank and caused damage near the village of Fornazzo. From a depth of several kilometers, magma is pushing its way toward the surface, cutting the flank of the mountain like a wedge, breaking rocks and thus generating hundreds of earthquakes.

Early in the afternoon on 17 March, at about 2625-2500 m elevation, the northern flank of Etna rips open, and thus initiates one of the most dramatic and destructive eruptions of Etna in the 20th century, an event of very short duration but with an extremely violent and rapid dynamic evolution. In only two days, lava flows inundate and devastate forests, cultivated land, wineyards, country and weekend houses; they interrupt roads, railroads, and cut power and telephone lines. The lava flows narrowly miss the scenic town of Randazzo and the nearby hamlet of Montelaguardia, failing to repeat the disaster of 1928, when the village of Mascali was nearly completely destroyed by a lava flow. Eruptions of this type represent one of the extreme scenarios for the Etna region also in the near future, especially if they were to occur in the most densely populated sectors of the volcano on the south and southeastern flanks.

 
The start of the eruption is observed directly by volcanologists flying over the volcano in a helicopter, having anticipated (and publicly forecast) the eruption. At 13:37 h on 17 March 1981, a system of eruptive fissures starts to open between 2625 and 2500 m altitude on the northern flank of etna. Accompanied by lava fountains and occasional phreatomagmatic explosions caused by interaction of the hot magma with a thick sheet of snow covering the volcano, several lava flows of minor volume are emitted. In the meantime, the eruptive fissure system continues to propagate toward NNW, into the direction of the town of Randazzo. On the evening of 17 March, a new fissure segment opens around 1800 m elevation, from which a voluminous and vigorously fed lava flow starts to advance at exceptional speed toward north, seriously threatening the little village of Montelaguardia, a few kilometers east of Randazzo.

The eruptive fissure system propagates further downslope during the early hours of 18 March, and on the late forenoon reaches 1400 m elevation. While the most voluminous lava flow (issuing fromt he fissure at about 1800 m) is following a path that passes between Randazzo and Montelaguardia, new flows emitted from the lowermost vents start advancing directly toward Randazzo. In a few hours, the main lava flow destroys dozens of country houses and weekend homes, and buries vast areas of cultivated land, then cuts the main lifelines connecting Randazzo to the Ionian coast (the Circumetnea and State railroads, the State Road 120, and several other roads). Finally slowing, the flow eventually reaches the bed of the Alcantara river, coming to a halt without touching the river itself, at a distance of 7.5 km from its source vents.

Meanwhile, the eruptive fissure system continues to propagate downslope, eventually terminating on the afternoon of 18 March with the opening of a group of small vents at 1250-1115 m elevation, from which only minor volumes of lava are emitted. The eruption finally starts to show signs of losing momentum, and the lava flow that has been directly threatening Randazzo starts to slow its advance. For a few more days, until 23 March, weak Strombolian activity continues at the lowermost vents, only feebly feeding the lava flow heading toward Randazzo, which eventually stops at 2 km distance from the first houses of the town.

The total volume of lava emitted in this eruption is estimated at 18-30 million m3; new studies indicate a volume of ~20 million m3. In spite of this relatively modest volume, the rates of lava effusion during the first two days of the eruption have reached exceptional peak values of about 300-600 m3 per second.

Etna_1981_01_400

Spectacular image of the eruptive theater of March 1981 on the Etnean slope above the town of Randazzo. The lava flows, which pass only 1 km to the east of the town to reach the bed of the Alcantara river, are seen in the center of the photograph. Photo taken from the book "Etna, storia di un vulcano" by Pietro Nicolosi (Tringale Editore, 1983)

Etna_1981_04_400

18 March 1981, the main lava flow interrupts the Circumetnea railroad immediately to the east of Randazzo. This lava flow cuts virtually all lifelines on the northern slope of Etna, including the State Railroad. Photo by John Guest, taken from the book "Mount Etna, the Anatomy of a Volcano" (Chapman & Hall, 1985)