Relationship between Gas Ratios and Eruption Styles: Real-Time Monitoring at Stromboli Volcano

We present our findings on the correlation between the CO₂/SO₂ molar ratio of volcanic gas in the plume and the hourly frequency of Strombolian explosions recorded at Stromboli from April to December 2024. Throughout this period, the two time series exhibited alternating weeks-long phases of synchronous variations and periods of decoupling, where one signal would increase while the other remained constant. In general, periods of high CO₂/SO₂ ratios were associated with an increased frequency of explosions. In the period preceding the paroxysm that occurred on 11 July 2024, the CO₂/SO₂ ratios experienced a sharp decline, coinciding with a rise in explosion frequency until June 28, when a lava overflow occurred, after which the frequency decreased rapidly. Following the paroxysm, we observed a gradual increase in the CO₂/SO₂ ratio through the end of December, along with a moderate increase in explosion frequency, albeit with similar fluctuations. It is known that the volcanic gases causing the explosions originate from deeper magmatic sources that exhibit a higher CO₂ content. The observed relationship between the variation in gas composition and the frequency of explosion suggests a potential causal relationship; nevertheless, the exact mechanisms underlying this association have yet to be comprehensively delineated. Long-term time series data and additional research are essential for a more comprehensive understanding of the relationship between the CO₂/SO₂ ratio and explosion frequency, as well as their links to volcanic processes and eruption forecasting. These findings enhance our understanding of Stromboli's degassing dynamics, the interplay between gas compositions and eruption frequency, and the styles of volcanic activity. They also underscore the importance of real-time monitoring of plume gas emissions to improve our understanding of magmatic dynamics at Stromboli and other basaltic volcanic systems.