Activating and reactivating pairs of nested collapses during caldera-forming eruptions: Campi Flegrei (Italy)

A structural model for Campi Flegrei Caldera (CFC; Italy), one of Earth’s most hazardous calderas, is provided. Data from the north (outer) rim show that this formed by downsag soon after the Neapolitan Yellow Tuff emplacement (~15 ka). Campanian Ignimbrite's (CFC’s other major eruption; ~39 ka) displacement at depth suggests the activity of a buried caldera fault. During the Campanian Ignimbrite eruption the north rim was activated as caldera-bounding fault and during the Neapolitan Yellow Tuff eruption as downsag. Previously published data reveal an inner collapsed structure, formed during the Campanian Ignimbrite eruption and reactivated during the Neapolitan Yellow Tuff eruption. So, CFC consists of 2 nested depressions, both active during the Campanian Ignimbrite and Neapolitan Yellow Tuff eruptions, but with different amounts of collapse. CFC is a major example of how 2 nested calderas may: (1) form during the same collapse episode; (2) be reactivated together during caldera-forming eruptions.