Abstract

Lascar volcano, located in the Central Andes Volcanic Zone, is one of the most active volcanoes in Northern Chile, characterized by recurrent minor explosive events. We have analyzed the volcanic degassing process at Lascar between August 2017 and August 2021 (Continental Chile: Alternates between UTC-4 (winter time) and UTC-3 (summer time)). using a multiparametric approach that integrates seismicity, visual observations, satellite thermal data, and ground-based SO2 flux measurements, which were deseasonalized to remove meteorological artifacts. This correction revealed intrinsic volcanic variations that allowed us to identify three distinct patterns: i) Pattern I-Overpressure and System Sealing (August 2017-January 2018), characterized by low deseasonalized SO2, emission rates despite frequent valid measurements, minimal thermal activity, and increasing long-period seismicity, indicating progressive sealing of the shallow system and internal pressurization, ii) Pattern II Pressurization, Fracturing, and Partial Unsealing (February 2018-November 2018), involves pressurization and mechanical failure of the conduit, marked by the appearance of tornillo and volcano-tectonic seismicity, followed by partial unsealing and increased gas release, iii) Pattern III-Explosion, Decompression, and Cycle Reset (November 2018-February 2020), correspond to explosive decompression, starting in the 22 November 2018 with ash emission event, followed by peak SO2 fluxes and transient thermal anomalies. Post-eruptive observations show that this event did not establish a stable equilibrium but reset the volcanic cycle, with the repetition of sealing and pressurization phases between 2020 and 2021. These results indicate that conduit sealing and rupture are recurrent processes that control Lascar's recent activity and highlight the importance of integrated gas, seismic, and thermal monitoring for identifying pressurization phases preceding minor explosive events.