Seafloor doming driven by degassing processes unveils sprouting volcanism in coastal areas.

Salvatore Passaro,Marco Sacchi,Franco Tassi,Giovanni Chiodini,Guido Ventura,Luciano Giannini,Orlando Vaselli,Stella Tamburrino,Mattia Vallefuoco,Stefano Caliro,Andrea Luca Rizzo

doi:10.1038/srep22448

Abstract

We report evidences of active seabed doming and gas discharge few kilometers offshore from the Naples harbor (Italy). Pockmarks, mounds, and craters characterize the seabed. These morphologies represent the top of shallow crustal structures including pagodas, faults and folds affecting the present-day seabed. They record upraise, pressurization, and release of He and CO2 from mantle melts and decarbonation reactions of crustal rocks. These gases are likely similar to those that feed the hydrothermal systems of the Ischia, Campi Flegrei and Somma-Vesuvius active volcanoes, suggesting the occurrence of a mantle source variously mixed to crustal fluids beneath the Gulf of Naples. The seafloor swelling and breaching by gas upraising and pressurization processes require overpressures in the order of 2–3 MPa. Seabed doming, faulting, and gas discharge are manifestations of non-volcanic unrests potentially preluding submarine eruptions and/or hydrothermal explosions.

Highlights

The Gulf of Naples forms the western margin of the Plio-Quaternary, NW-SE elongated Campanian Plain structural depression[13,14,15]
The Digital Terrain Model (DTM) shows that the seafloor south of the harbor of Naples is characterized by a southward facing, gently dipping surface interrupted by a 5.0 × 5.3 km dome-like structure, locally known as Banco della Montagna (BdM) (Fig. 1a,b)
The spatial density of the cones and pockmarks evidences major NE-SW alignments delimiting the northeastern and southwestern boundary of the BdM dome (Fig. 4a,b); less extended NW-SE alignments are in the BdM central sector

Summary

Introduction

The Gulf of Naples forms the western margin of the Plio-Quaternary, NW-SE elongated Campanian Plain structural depression[13,14,15]. The gulf is confined to the north by the E-W arranged, active volcanoes of Ischia Island (from about 150 ka to 1302 AD), Campi Flegrei caldera (from about 300 ka to 1538 AD), and Somma-Vesuvius www.nature.com/scientificreports/. Campi Flegrei and Somma-Vesuvius are characterized by hydrothermal manifestations, ground deformation, and shallow seismicity[16,17,18] (e.g., the 1982–1984 unrest episode of Campi Flegrei with an uplift of 1.8 m and thousands of earthquakes). The volcanic activity in the last 36 ka at Campi Flegrei and 18 ka at Somma Vesuvius, and the sea level oscillations have controlled the depositional system in the Gulf of Naples[21]. Submarine gas emissions have been recognized around Ischia Island and offshore near the coast of Campi Flegrei and Somma-Vesuvius (Fig. 1b)

Methods

Results

Conclusion