Identifying changes on volcano unrest condition and tracking the evolution of eruptive activity are fundamental for volcanic surveillance and monitoring. Under this perspective, magmatic gases play a key role; therefore, monitoring changes in volcanic plume composition is essential.

Between and during each eruption large systematic variations in the volcanic plume composition can be observed on Mt. Etna. Specifically, gas emissions implicitly contain critical information on the state of the volcano in terms of magma dynamics in the plumbing system.

New technologies have improved the ability to identify gas emissions through remote sensing. Since March 2000, the remote sensing group of INGV-OE Catania has regularly measured the volcanic gas in the plume emitted from Mt. Etna by solar occultation FTIR on average 2-3 acquisitions per week. These measurements allow to quantify the column amounts of SO2, HCl and HF in the path between the instrument and the Sun, and obtain SO2/HCl, HCl/HF and SO2/HF ratios

Extracting meaningful information and gaining new insights from 23 years data collection is a challenging task. Here, we perform a data driven investigation exploiting the relationships between volcanic activity and volcanic gas emissions from 2000 to 2023 period. A general decrease in SO2/HCl ratio, due to an increase in the halogens emission rate (HCl and HF), is observed during eruptions that results closely connected with the central conduit of Etna (e.g. 2004 and 2008).This evidence suggests that magma residence time is required to sustain an efficient halogen degassing via summit craters and the lava flow draining gradually led to a break in the magma convective overturn within a shallow reservoir. Whereas, eruptions not connected with the central conduit of Etna (e.g. 2002-03) are preceded by several weeks of elevated SO2/HCl ratio, produced by a relative reduction in HCl emission consistent with inefficient magma circulation that partially inhibits ascent of magma thought the central conduit of Etna enhances the probability of lateral eruptions.