Réunion

Réunion is a French overseas department in the Indian Ocean, approximately 700 kilometres east of Madagascar, and one of the world's most volcanically active islands. The island is built entirely on the Réunion hotspot — the same mantle plume responsible for the Deccan Traps flood basalts and the Chagos-Laccadive Ridge. The hotspot is currently active beneath the southeastern part of the island, where the Piton de la Fournaise shield volcano erupts an average of once or twice per year. The northwestern part of the island is dominated by the older, extinct Piton des Neiges massif, which reaches 3,069 metres — the highest point in the Indian Ocean.

Seismicity at Réunion is dominated by volcano-tectonic activity beneath Piton de la Fournaise. Each eruptive episode is preceded and accompanied by hundreds to thousands of small [[seismic-wave]] events as magma forces its way through the volcanic edifice. These volcanic earthquakes are shallow — typically less than 5 kilometres deep — and rarely exceed [[magnitude]] 3.5 at the surface. Tectonic seismicity is minor; the island sits on the relatively stable interior of the Indo-Australian Plate, and no active tectonic faults are mapped beneath it.

The primary hazard beyond volcanic earthquakes is [[tsunami]]. Réunion's coastlines are vulnerable to locally generated waves if a large volcanic flank collapse occurred on Piton de la Fournaise — a concern supported by massive ancient underwater landslide deposits on the eastern submarine slope. The 2004 Indian Ocean [[tsunami]] reached Réunion but caused only minor wave heights due to offshore bathymetric geometry. The REVOSIMA and IPGP observatories operate comprehensive [[seismograph]] networks for continuous monitoring of volcanic and tectonic signals.