Caldera’s Breathing: Poroelastic Ground Deformation at Campi Flegrei (Italy)

Micol Todesco

doi:10.3389/feart.2021.702665

Abstract

Ground deformation at Campi Flegrei has fuelled a long-term scientific debate about its driving mechanism and its significance in hazard assessment. In an active volcanic system hosting a wide hydrothermal circulation, both magmatic and hydrothermal fluids could be responsible, to variable degrees, for the observed ground displacement. Fast and large uplifts are commonly interpreted in terms of pressure or volume changes associated with magma intrusion, while minor, slower displacement can be related to shallower sources. This work focuses on the deformation history of the last 35 years and shows that ground deformation measured at Campi Flegrei since 1985 is consistent with a poroelastic response of a shallow hydrothermal system to changes in pore pressure and fluid content. The extensive literature available for Campi Flegrei allows constraining system geometry, properties, and conditions. Changes in pore pressure and fluid content necessary to cause the observed deformation can then be calculated based on the linear theory of poroelasticity. The predicted pore pressure evolution and fluid fluxes are plausible and consistent with available measurements and independent estimates.

Highlights

Caldera deformation stirs scientific debates about the actual source driving ground displacement and the crucial implications for hazard assessment
The post-1985 ground displacement observed at Campi Flegrei include a 20-years-long subsidence phase followed by a 15-yearslong uplift
The results presented here do not exclude the possible involvement of magma in driving the recent deformation at Campi Flegrei

Summary

Introduction

Caldera deformation stirs scientific debates about the actual source driving ground displacement and the crucial implications for hazard assessment. The Campi Flegrei caldera is a unique case history, with an impressive data set that describes ground deformation over a century, including three significant uplift phases starting in 1950, 1969, and 1982 (Del Gaudio et al, 2010). Each uplift episode lasted a couple of years or less and together totaled more than 3.5 m of ground displacement (Figure 1A). Uplift resumed after 2005 (De Martino et al, 2014) initially at a slow rate, which increased in 2012 (Figure 1B), causing a shift in alert level from green to yellow (Attention). This uplift phase is still going on, uninterrupted, at the time of writing (2021).

Methods

Results

Discussion

Conclusion