Calderas and magmatic feeding systems: examples from Campi Flegrei (Southern Italy)

High magnitude, caldera-forming eruptions worldwide are mostly fed by high-silica, often alkaline magmas such as rhyolites, trachytes and phonolites. Before erupting, these silicic magmas stagnate within large intra-crustal reservoirs, which are commonly thought to be withdrawn in short times during caldera collapses and related eruptions. Many combined volcanological and geochemical investigations have been carried out in the past tens of years on large calderas and related silicic products from worldwide, in order to understand how the magmatic feeding systems of calderas work. The Campi Flegrei caldera is one of the best studied examples. Many investigations have been carried out on Campi Flegrei and on other large calderas with the aim of explaining: i. mechanisms and times of formation, growth and withdrawal, of large magma reservoirs feeding caldera-forming eruptions; ii. triggering mechanisms of large caldera-forming eruptions; iii. relationships between regional tectonic and volcanic structures on which calderas establish; iv. role of magma chemistry in the dynamics of large eruptions, particularly during caldera collapse episodes; v. relationships between volcanic activity of calderas and their magmatic feeding systems. The results of these studies have highlighted the complex behavior of the Campi Flegrei caldera magmatic feeding system through time, with periods of time characterized by open system behavior marked by replenishment of geochemically and isotopically distinct magma, alternated with periods of time characterized by closed system behavior. Furthermore, the data for the largest magnitude Campanian Ignimbrite and Neapolitan Yellow Tuff eruptions, as well as for small magnitude eruptions, such as Agnano-Monte Spina, cast evidence for close relationships among eruption dynamics, activation of local and regional structures, large- and small-scale collapse events, composition of magmas and magma evolution processes, both closed- and open-system. Understanding all these characteristics is fundamental in volcanic hazard assessment and risk mitigation, and particularly in constructing hazard maps.