SUPPLEMENTARY INFORMATION to: Longevity, evolution and eruption potential of the Campi Flegrei caldera Giordano et al. 2026, Geology

The longevity of volcanic activity at calderas provides first order information on the potential for eruptions of different magnitudes to occur. Yet this parameter is commonly severely underestimated for the limited access to the oldest volcanic sequence, collapsed within caldera depressions and/or buried by younger deposits. In this paper we reassess the longevity at Campi Flegrei, arguably the caldera most at risk on Earth, by determining the age and composition of accessory lithics and xenocrystals. We show that magmatic activity started at least 796 ± 100 ka, extending previous knowledge by more than 500 kyrs. Ages distribution and magma compositions indicate that the Campi Flegrei plumbing system evolved over time reaching thermal maturation for a caldera system in the last 100-150 ka, at an average eruption rate of 9.14 x 10-4 km3/yr and maintaining its potential for future VEI7 caldera-forming eruptions.