Variations in CO2 emissions at a mud volcano at the southern base of Mt Etna: are they due to volcanic activity interference or a geyser-like mechanism?

Abstract

Mud volcanoes are often associated with large areas of CO2 and CH4 emission that are potentially dangerous due to sudden paroxysmal gas and mud eruptions. Despite the interest in understanding such natural environments, they have not yet been thoroughly investigated and a single interpretative framework remains to be elaborated. This lack of knowledge may be due to the difficulty in measuring in-plume CO2 as there is very little contrast with atmospheric CO2, coupled with the complex organizational strategies required for long-term monitoring. This work features three different methods that were used to evaluate the CO2 flux at the Salinelle mud volcano in the foothills of Mt Etna (Italy), carried out periodically from December 2013 to April 2018. We computed in-plume CO2 flux indirectly using a tunable laser and a portable MultiGAS and, directly, measuring the gas volumetric flux from bubbling pools. The morphological variations of the mud field were recorded using unmanned aerial vehicle (UAV) imagery, which provided information on the migration of vents in relation to the observed variations in measured gas output. Our analysis shows that the three methods gave comparable values, indicating the feasibility of this approach. Our findings suggest a pseudo-cyclical pattern in the bulk CO2 emitted at Salinelle, introducing a new interpretation of the processes involved in mud volcano dynamics. We theorize that the periodic variation of the gas emitted at the Salinelle may be attributed to a “geyser-like” mechanism that may be subject to interruption or changes in magnitude by volcanic or seismic events.