A Volcano Still Moving Beneath the Sea

300 volcano-tectonic earthquakes, 139 long-period earthquakes, and 2 very long-period earthquakes have been recorded in the “Horseshoe” area, off the coast of Petite-Terre, according to the latest bulletin from the Mayotte Volcanological and Seismological Monitoring Network (REVOSIMA), published in March 2026.

These figures confirm ongoing seismic activity in the subsurface, between 20 and 50 km deep. This activity is concentrated east of Petite-Terre, in an area located between 5 and 15 km from the coast. Volcano-tectonic earthquakes reflect rock fractures caused by magma pressure. Long-period earthquakes are associated with the movement of fluids such as gases or magma. Very long-period earthquakes, which are rarer, indicate slower and deeper movements of the system.

From March 1st to 31st, 2026, the observatory recorded an average of four detectable earthquakes per day. This level is considered stable, with no significant change compared to previous months.

To supplement this data, REVOSIMA scientists used a glider, an underwater robot, to explore known gas emission zones. Measurements show that degassing remains generally stable and close to levels observed for several years.

The analyses primarily indicate the presence of carbon dioxide, a gas originating from deep within the Earth. This confirms ongoing volcanic activity beneath the ocean floor. Some unusual signals were detected between certain areas, but they do not indicate the emergence of a new major site.

According to REVOSIMA, current data do not show any major changes in the situation. The Fani Maoré volcano has likely been inactive since 2021, but its future remains uncertain.

Scientists are considering several possible scenarios: a complete shutdown, a resumption of activity, or even a new eruption elsewhere in the area. For now, the situation remains stable, but monitoring continues to track any changes in the volcanic system.