Insular shelves as a tool for reconstructing the evolution of volcanic islands

Abstract

The erosion by waves, accomplished at different elevations due to glacio-eustatic sea-level fluctuations and islands’ vertical movements, carves the flanks of volcanic islands resulting in the formation of insular shelves, features long known in literature since the early paper of Menard (1983). However, a systematic study of their morphometric parameters and evolution has seldom been carried out. This Ph.D project, based on high-resolution multibeam bathymetric data and seismic reflection profiles collected in the last decades by the University of Bologna, University of Rome “La Sapienza”, CNR-IGAG Rome and by the Hydrographic Institute of the Portuguese Navy, explores the geomorphologic and structural features of the shelves surrounding the volcanic islands of Salina, Lipari and Vulcano in the Central Aeolian Archipelago and Santa Maria in the Azores Archipelago, respectively. The main aim is to increment our knowledge regarding the processes that influence the formation and the evolution of insular shelves and how these features might help us to better constraint the volcanic history of such islands. The study of insular shelves helps to improve the evolutionary models of the studied volcanic islands, which were previously developed only from the knowledge of the onshore geology. The information derived from the measured morphometric parameters (mainly the shelf width and the erosive edge depth) were integrated with field studies, allowing to infer, in some cases, the possible location of their earlier evolutionary stages, as well as to improve the overall geological evolution of studied volcanic islands.In the Central Aeolian sector, we thus document the occurrence of presently submerged and largely dismantled volcanic edifices predating the oldest complexes located onshore. At Santa Maria we adopted the same integrated approach to relate the morphologic characteristics of the shelf with the geology onshore.