Evolution of SO2 Emissions from Nyiragongo Volcano as Recorded at Rusayo DOAS Station from 22nd May, 2021 to 20th May, 2023

Nyiragongo and Nyamulagira are two still active volcanoes in the Virunga volcanic chain.However, Nyiragongo remains the most threatening given the human population and goods in its proximity.Given the disappearance of the gas plume and the lava lake in the crater, some residents of the City of Goma and its surroundings were tempted to believe that Nyiragongo was extinct or got dormant after its eruption on 22nd May, 2021.Others have thought that there was an eruptive cycle for Nyiragongo and which should guide estimates regarding the occurrence of a next eruption.This study was conceived to understand, thanks to mini DOAS, the evolution of SO2 emissions as an indicator of the activity of Nyiragongo on a scale of two years after its eruption of 22nd May, 2021.The absorption spectrometry, performed using the Differential Optical Absorption Spectrometer, DOAS, an ultraviolet based instrument settled in Rusayo helped to collect the sulfur dioxide emitted from Nyiragongo during the study period.Results revealed that the longer disappearance period of the SO2 emissions from Nyiragongo (n=98) was recorded from 22nd May to 29th August 2021 directly after the eruption, about three months.At each reappearance of the volcanic SO2 emission during the study period, the average amount recorded where not very different with the amounts observed during other volcanic normal activities.While the lowest average was 297.28 tons/day recorded on 3rd September 2022, the highest average reached 7845.24t/d on 16th January 2022; fortunately, it raised to that extent just the only one day and the trend line for the period remained between 1500 t/d and 700t/d.The longer disappearance could last no more than three months before its reappearance.These observations indicated clearly that Nyiragongo volcano remained active even after the eruption of 22nd May 2021.The volcanic SO2 monitoring should be reinforced and maintained properly to avoid all false considerations about the volcanic activity of Nyiragongo.All signs of volcanic activity should be popularized among all stakeholders of the volcanic risk prevention around Nyiragongo, especially those living in Goma, Gisenyi and the surrounding villages.