Evidence of thermal-driven processes triggering the 2005–2014 unrest at Campi Flegrei caldera

Abstract

An accelerating process of ground deformation that began 10 years ago is currently affecting the Campi Flegrei caldera. The deformation pattern is here explained with the overlapping of two processes: short time pulses that are caused by injection of magmatic fluids into the hydrothermal system; and a long time process of heating of the rock. The short pulses are highlighted by comparison of the residuals of ground deformation (fitted with an accelerating polynomial function) with the fumarolic CO2/CH4 and He/CH4 ratios (which are good geochemical indicators of the arrival of magmatic gases). The two independent datasets show the same sequence of five peaks, with a delay of ∼200 days of the geochemical signal with respect to the geodetic signal. The heating of the hydrothermal system, which parallels the long-period accelerating curve, is inferred by temperature–pressure gas geoindicators. Referring to a recent interpretation that relates variations in the fumarolic inert gas species to open system magma degassing, we infer that the heating is caused by enrichment in water of the magmatic fluids and by an increment in their flux. Heating of the rock caused by magmatic fluids can be a central factor in triggering unrest at calderas.