In September 2026, seismic and volcanic activity continues to be present near Mayotte, an island in the Indian Ocean. Hundreds of earthquakes have been recorded, and gas emissions remain active in the underwater area of Fer à Cheval. Between 1 and 30 September 2026, teams from REVOSIMA, a research organization, detected 265 volcanic-tectonic earthquakes, 84 long-period earthquakes, and one very long-period earthquake between Mayotte and the underwater volcano Fani Maoré. The activity was mainly concentrated to the east of Petite-Terre, at depths between 20 and 50 kilometers. While the situation is less intense than during the initial crisis in 2018, scientists continue to closely monitor the area. In September, 114 earthquakes could be precisely located manually: 89 volcanic-tectonic earthquakes and 25 long-period earthquakes. Among the volcanic-tectonic earthquakes, 11 had magnitudes between 2 and 3, and two exceeded magnitude 3. However, the majority of events remain of low magnitude. The decrease in activity does not mean the phenomenon is over. REVOSIMA reminds that a reduction in seismic energy does not confirm that magma is no longer circulating at depth. Monitoring efforts have also been strengthened in recent years. Since the end of 2024, the seismic network has been expanded, and detection methods have been improved through the use of a network capable of recognizing seismic waves. These advancements allow the detection of increasingly weaker earthquakes. Underwater monitoring is also crucial, particularly in the Fer à Cheval area, an underwater volcanic structure located in the seismic swarm near Mayotte. Scientists have observed emissions there for several years, accompanied by clouds that can rise more than 1,200 meters above the seabed and be detected up to a hundred meters below the surface. In total, 23 emission sites have been identified in this area. During the 2025 campaign, 17 of them were still productive. Analysis of the fluids provides information on what is happening at depth. They are composed almost entirely of carbon dioxide at 99%, as well as methane and small amounts of hydrogen. This activity is not limited to the seabed. Since 2021, an increase in gas flow, particularly carbon dioxide, has also been observed in Lake Dziani Dzaha, a crater lake on Mayotte. Scientists note that gases rising from the Earth's depths are becoming increasingly present. Since 2023, their composition shows an evolution similar to that observed at the beginning of the volcanic activity in 2018. The underwater volcano Fani Maoré remains a central focus of research, despite the latest observations not showing a new lava flow. The last direct evidence of activity dates from 22 October 2020. According to available data, the eruption likely ended on 4 December 2020, but this hypothesis is not certain. Scientists do not completely exclude a resumption of the eruption. Three possibilities remain: the eruption could have definitively ended, it could resume at the same site, or new activity could appear elsewhere. However, the persistence of seismicity and CO2 emissions in the area prevents a clear determination of what is happening under the seabed. Since the end of 2020, the signals have become too weak to allow a comparable interpretation. In September 2026, the autonomous robot SeaExplorer also participated in the monitoring. For more than 290 hours, it traveled approximately 345 kilometers between 800 and 1,250 meters in depth and sampled several areas where fluid emissions were occurring. The results correspond to previous observations, and no major new emission area has been clearly identified in the explored sectors. For scientists, the case remains far from closed. Seismicity has significantly decreased since the beginning of the crisis, but it continues, fluid emissions remain active, and the available data do not yet allow knowing how the phenomenon will evolve.