Transition from spot to long-lived eruptive activity in continental rifting tracked by monitoring soil degassing

Mechanisms responsible for either spot or long-lived eruptive activity at frequently erupting volcanoes remain poorly deciphered in continental rifting. It is the case in the Virunga Volcanic Province (VVP), belonging to the East African Rift System (EARS), where the dynamics of the eruptive activity at the neighboring Nyiragongo and Nyamulagira volcanoes are complex and highly variable. Following the latest lava-lake drainage event at Nyiragongo on May 22, 2021, the eruptive activity in the VVP alternated between the two volcanoes and punctuated by periods of quiescence. Unprecedented monitoring of soil CO 2 and Rn degassing was carried out during this peculiar period to evaluate the ability of this technique to decipher the complex magmatic and tectonic processes inherent to magmatic activity in continental rifting. A main soil degassing anomaly was identified during the first semester of 2024, preceding the renewal of continuous and intense eruptive activity at both volcanoes, as evidenced by massive SO 2 emissions and thermal anomalies in the crater areas. Comparison with local seismic activity reveals a close relationship between soil degassing and volcanic seismic signals able to be used to track deep magma replenishment and pressurization followed by magma transfer toward shallower levels. Our results provide insights into potential triggers of the eruptive activity in continental rifts. • Soil degassing monitoring is efficient to track deep magma transfer in continental rifting. • Major magma batch may trigger lava lake renewal.