Abstract

The identification of the mechanisms responsible for the deformation of calderas is of primary importance for our understanding of the dynamics of magmatic systems and the evaluation of volcanic hazards. We analyze twenty years (1997–2018) of geodetic measurements on Ischia Island (Italy), which include the Mt. Epomeo resurgent block, and is affected by hydrothermal manifestations and shallow seismicity. The data from the GPS Network and the leveling route show a constant subsidence with values up to −15 ± 2.0 mm/yr and a centripetal displacement rate with the largest deformations on the southern flank of Mt. Epomeo. The joint inversion of GPS and levelling data is consistent with a 4 km deep source deflating by degassing and magma cooling below the southern flank of Mt. Epomeo. The depth of the source is supported by independent geophysical data. The Ischia deformation field is not related to the instability of the resurgent block or extensive gravity or tectonic processes. The seismicity reflects the dynamics of the shallow hydrothermal system being neither temporally nor spatially related to the deflation.

Highlights

  • The deformation of calderas may be associated with different processes, including the magma accumulation, lateral migration or withdrawal, increase or decrease of gas pressure of hydrothermal systems, and variations in the degassing rate of magma chambers [1]

  • While uplift phases are indicative of resurgence and may be precursors of volcanic eruptions, testifying to a pressurization of the magmatic system due to magma/gas accumulation or upward magma/fluid migration, subsidence episodes are more difficult to interpret because they may be related to different causes, such as magma cooling and degassing [2], lateral magma migration in sills [3], depressurization of hydrothermal reservoirs [4], regional extension related to tectonics, and gravity instability processes [5]

  • To better understand the Ischia velocity field, we focused on the island, showing the horizontal velocity field with respect to the island centroid

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Summary

Introduction

The deformation of calderas may be associated with different processes, including the magma accumulation, lateral migration or withdrawal, increase or decrease of gas pressure of hydrothermal systems, and variations in the degassing rate of magma chambers [1]. While uplift phases are indicative of resurgence and may be precursors of volcanic eruptions, testifying to a pressurization of the magmatic system due to magma/gas accumulation or upward magma/fluid migration, subsidence episodes are more difficult to interpret because they may be related to different causes, such as magma cooling and degassing [2], lateral magma migration in sills [3], depressurization of hydrothermal reservoirs [4], regional extension related to tectonics, and gravity instability processes [5] This is difficult when the subsidence is associated with seismicity. Aiming to recognize the different causes of the recorded subsidence of Ischia’s (Italy) resurgent caldera (Figure 1), we analyze

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