The San Biagio ‘Salinelle’ mud volcanoes (Belpasso, Sicily): a preliminary 3D subsoil model

The Etna area is affected not only by volcanic activity related to the Mount Etna volcano, but also by manifestations of secondary volcanism located at some distance from the main volcano conduit and known as ‘mud volcanoes’. In the lower border of the volcanic edifice occur some manifestations of mud volcanism. These phenomema are classed as pseudo-volcanic manifestations, originating from the presence of natural gases under pressure in the subsurface, but It is not fully clear if and how the activity of the mud fields would be connected with the volcanic activity of Mt. Etna.The activity of these mud volcano is characterized by a persistent emission of muddy water mixed with salts, which rises to the surface due to the gas pressure in the subsoil (Kopf 2002). These gases tend to rise through preferential migrating pathways due to the presence of permeable rocks and/or lithological discontinuities, carrying water, mud, rock fragments and hydrocarbons as they ascend. The San Biagio Salinelle are one of the three mud volcano fields located around the Paternò eruptive monogenic apparatus; this volcanic structure is one of the first sub-aerial volcanic manifestations that formed in the pre-etnean phase. Non-invasive geophysical surveys were carried out in the area of the active cone of the San Biagio Salinelle, in order to identify the shallow ascent path of the emitted products. In particular, environmental noise samplings (Nakamura Y, 1989) were taken at the nodes of a specially designed grid and subsequently the Vs values were acquired through an active seismic survey. Finally, a digital elevation model of the area (DEM), was obtained by a topographic survey, carried out with the GNSS technique (Global Navigation Satellite System), in RTK mode (Real Time Kinematic). The DEM and the topographic benchmark installed will represent the reference surface that will allow an accurate comparison with future surveys to measure all the deformations affecting the mud volcano. The data from the applied methods have been integrated and interpreted to obtain a 3D representation of the surface and a possible model showing the shallower feeding system of the investigated mud volcano. The adopted technique is fast and cost-saving, and its application to the other mud volcanoes in the area will enable their comparison and help shed some light on the factors controlling the mud volcanism in the area. Paroxystic mud eruptions can cause damage to buildings, roads, and inconvenience to the local people. The study of the San Biagio salinelle is a first step towards a more complete multidisciplinary characterization of this process with a view to mitigating risk.