Eruptive activity and tsunamigenic landslides at Stromboli volcano (Italy): clues from deposits and future perspectives

Abstract

Tsunami deposits are the main evidence of past tsunami wave inundations but are inherently difficult to identify in coastal sediment sequences. The complexity of the process and the multiple interactions with the ground generate a plethora of sedimentary features such as layers of sand and gravel that were typically interpreted in the past as marine transgression events or as storm surges of extraordinary magnitude. Only in the eighties, seminal works highlighted some specific features that allow identification of their origin. Among the variety of triggering mechanisms, landslides occurring on steeply sloped coastal areas, coastal volcanoes or volcanic islands, have been shown to produce devastating tsunamis. Surprisingly, there are only a few clear examples worldwide of the relationship between volcanic activity and landslides. Based on radiocarbon ages, on stratigraphic, volcanological and archaeological evidence, three well-preserved medieval tsunami deposits were recently discovered along the coast of Stromboli volcano (Aeolian Islands, southern Italy) as shown by Rosi et al. (2019), who suggested that the destructive power of one of these events is also possibly related to a huge marine storm that devastated the port of Naples in 1343 (200 km north of Stromboli). The sedimentological study of the deposits has allowed a detailed characterization of the tsunami sequences intercalated with volcaniclastic deposits and primary tephra and allowed reconstruction of the likely sequence of the volcanic events (Pistolesi et al., 2020). In one case, a violent explosion possibly preceded the tsunami, whereas in the youngest event, the lateral collapse of the volcano flank triggered a tsunami wave that was rapidly followed by sustained explosive magmatic activity and ensuing prolonged ash venting. The hypothesized tsunami-triggering dynamics suggests a close link between volcanic activity and flank collapse, further confirming that the persistent activity at Stromboli makes the volcano particularly susceptible to tsunami generation, confirming the hazard of these phenomena at a regional scale. New stratigraphic trenches carried out in late 2020 also revealed that deeper, older tsunami deposits may be present, suggesting that tsunami and tephra deposits have recorded interactions between past eruptive activity and landslides at Stromboli volcano even further back in the past.