The contribution of palaeomagnetism, tephrochronology and radiocarbon dating to refine the last 1100 years of eruptive activity at Vulcano (Italy)

Abstract

During the past millennia, several eruptions have occurred within the La Fossa caldera on the island of Vulcano (Aeolian Islands, Italy), some being also described in historical documents dating back to Republican Roman times (first to second century BC). The absolute and relative timing of such activity, however, has remained poorly defined and controversial, due to contrasting ages provided by radiometric and unconventional palaeomagnetic methods. Here, we present a detailed recon- struction of the eruptive history focused on the ninth to fifteenth century AD period that occurred at both La Fossa cone and Vulcanello. This integrated approach involves tephrostratigraphy, standard palaeomagnetic methodology and radiocarbon dating. The new dataset confirms that the lavas exposed above sea level at Vulcanello were erupted between the tenth and eleventh century AD, and not between the first and second century BC as previously suggested. In this same time interval, La Fossa cone was characterized by long-lasting, shoshonitic, explosive activity followed by a discrete, sustained, rhyolitic explosive eruption. Between AD 1050 and 1300, activity was focused only on La Fossa cone, with alternating explosive and effusive eruptions that emplaced four rhyolitic and trachytic lava flows, resulting in significant growth of the cone. After the violent, phreatic event of the Breccia di Commenda (thirteenth century), the eruption continued with a substantial, long- lasting emission of fine ash until activity ceased. Magmatic explosive activity resumed at La Fossa cone at the beginning of the fifteenth century marking the onset of the Gran Cratere cycle. This phase lasted until the mid-sixteenth century and produced at least seven explosive eruptions of intermediate magma composition and a couple of lateral explosions (Forgia Vecchia I and II). During this time interval, a third cinder cone was emplaced at Vulcanello, and the activity produced the lava flows of Punta del Roveto and Valle dei Mostri. From the seventeenth to twentieth centuries, volcanic activity was concentrated at La Fossa cone, where it ended in 1890. This work confirms that Vulcanello island formed in Medieval times between the tenth and eleventh centuries. Moreover, between the tenth and mid-sixteenth centuries, La Fossa caldera was the site of at least 19 eruptions with an average eruption rate of one event every 34 years. This rate makes volcanic hazard at Vulcano higher than that suggested to date.