The Serracozzo cave, Etna Volcano, Italy: A peculiar cavity developed during the 1971 flank eruption within an eruptive fissure and an arterial lava flow

The Serracozzo cave is one of the most famous and fascinating lava tubes of Etna volcano. The cave formed in about one month during the final phase of the well-known 1971 flank eruption. It is a morphologically complex volcanic cavity because of its dual-nature: the upper section developed directly within the eruptive fissure, while the lower part formed within a ravine by sealing of an arterial ‘a‘ā lava flow, resulting in a distinctive lava tube. The features of the cavity formed within the eruptive fissure reveal a pulsating emplacement of the feeder dike, with alternation of magma pressure build-up and release. The dike emplaced a structural weakness along the Etna’s NE flank, which was frequently intruded by several other dikes during previous historical lateral eruptions. During its way to the surface the dike progressed by pulses, expanding laterally and then upwards. The same pulses occurred during its propagation down slope, where we observed wide chambers alternated to narrow passages. The effusive vents at the top of the fissure became skylights that acted as pressure release valves, forming short pāhoehoe overflows around the vents with upper level cavities partially merging with the main one during lava drain back. To characterize the volcanic features of the cave and reconstruct its spatiotemporal evolution, we conducted a traditional geological field survey integrated with old photos taken during the eruption, historical topographic maps and previous field surveys. Furthermore, high-resolution digital models of both the internal and external environments were generated using Terrestrial Laser Scanning (TLS) and Unoccupied Aerial Systems (UAS). This study realized with a multi-proxy approach is extremely valuable for hazard assessment because it allows us to constrain the timing necessary for the development and growth of the internal and external lava tube features and of how they evolved with time.