Mayotte

Mayotte is a French overseas department in the Comoros archipelago at the northern entrance to the Mozambique Channel, between Madagascar and the East African coast. The Comoros islands are entirely volcanic in origin, built by a hotspot track that propagated eastward over the past 10 to 20 million years across the East African passive margin. The island chain is not positioned on an active plate boundary in the classic sense, but from late 2018 onward Mayotte became the site of one of the most extraordinary seismic and volcanic events in recent history.

Beginning in May 2018, Mayotte experienced an unprecedented [[seismic-wave]] swarm: over 35,000 events were recorded in the first two years, including a magnitude 5.9 event on 15 May 2018 — the largest earthquake ever recorded in the Comoros region. A large proportion of the [[seismic-wave]] signals were very-long-period tremors traced to a massive submarine volcanic eruption approximately 50 kilometres east-southeast of Mayotte at 3,500 metres depth. The newly formed submarine volcano, informally named "Fani Maoré," erupted over 5 cubic kilometres of lava within 14 months — one of the largest submarine eruptions ever documented — causing Mayotte to subside approximately 13 centimetres and shift 10 centimetres eastward as the magmatic chamber deflated.

The 2018–2019 event transformed understanding of hazard at Mayotte. The island is exposed to continued magmatic [[seismic-wave]] swarms and conventional tectonic seismicity from the diffuse Africa-Somalia plate boundary to the west. Given the low elevation of much of Mayotte and the dense coastal population, both [[tsunami]] risk from submarine mass movements and ongoing volcanic-tectonic hazard remain active concerns. Monitoring has been significantly expanded through the REVOSIMA network using seismometers, ocean-bottom instruments, and GPS receivers.