Geology & Geophysics News

Ancient Tsunami Tied to Volcanic Flank Collapse in Italy

Stromboli’s volcanic cone may have suffered multiple flank collapses between the 14th and 16th centuries, triggering tsunamis that led to the abandonment of the island.

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The Italian island of Stromboli has long attracted residents and visitors thanks to its mild climate, fertile soils, and picturesque views. But there’s a sinister side to Stromboli—the steep flanks of its active volcano periodically slough off, creating landslides that tumble into the sea and trigger tsunamis. Now, geoscientists and archaeologists have shown that one of these events in the 14th century was likely responsible for the rapid abandonment of the island. An enormous, deadly marine storm reported in Naples in 1343 was also probably due to the same tsunami waves, the researchers proposed. These findings suggest that southern Italy is at a higher risk of tsunamis than previously known.

Something Completely Different

Mauro Rosi, a volcanologist at the University of Pisa in Italy, and his colleagues excavated three trenches in the northeastern part of Stromboli to look for signs of ancient tsunamis. Working between 170 and 250 meters from the present-day shoreline, the researchers didn’t have to dig long before their machinery revealed something other than normal soil. “Below 1 meter, we immediately found something that was completely different,” said Rosi. Three clearly defined layers of pebbles and black sand emerged, “closely resembling what you see when you go to the beach,” said Rosi. This material, the researchers surmised, had been swept inland by tsunami waves.

To calculate approximately when these tsunamis occurred, the researchers used carbon-14 dating to age date charcoal fragments buried directly below the tsunami deposits. Rosi and his colleagues estimated that the three tsunamis inundated Stromboli between the 14th and 16th centuries. Focusing on the oldest and largest tsunami, the team found that no large, contemporaneous earthquakes were noted in historical records. The lack of a seismic event, paired with lava records showing a collapse of the volcano’s Sciara del Fuoco (Stream of Fire) lava feature around 1350, pointed to the tsunami waves being triggered by the collapse of the flanks of the volcano, the researchers concluded.

Graves in the Rubble

Rosi and colleagues also used archaeological evidence to show that the tile roof of a medieval church in northeastern Stromboli had collapsed right around the same time. The scientists also found three graves hastily dug in the collapsed tiles that contained human remains. Landslide-induced shaking might have irreparably damaged the church and killed people, the team proposed.

Further evidence of this tsunami might also be in literature. In November 1343, the writer Francesco Petrarca recorded a sea storm that pummeled the harbor of Naples, destroyed boats, and killed hundreds of people. It’s entirely conceivable that a tsunami originating on Stromboli could have swept 200 kilometers north and rolled up the shoreline of the Italian mainland, Rosi and his collaborators concluded. Communities in southern Italy may be “exposed to a much higher tsunami hazard than previously thought,” the researchers wrote last month in Scientific Reports.

This research “sheds new light on the persisting hazard of landslide-generated tsunamis in the Tyrrhenian Sea,” said Max Engel, a geomorphologist at the University of Cologne in Germany not involved in the research.

Rosi has a long history with Stromboli—his doctoral thesis in the 1970s focused on the island—and he is looking forward to continuing fieldwork there. In the future, he plans to dig deeper in search of even older tsunami deposits to study how often large waves have struck Stromboli. Extracting history from layers of sediments is hard, however, Rosi admits. “The identification of past tsunami is not an easy task.”

—Katherine Kornei ([email protected]; @katherinekornei), Freelance Science Journalist

Citation: Kornei, K. (2019), Ancient tsunami tied to volcanic flank collapse in Italy, Eos, 100, https://doi.org/10.1029/2019EO116083. Published on 11 February 2019.
Text © 2019. The authors. CC BY-NC-ND 3.0
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