Mascarene Islands - Nature - Geology

Geology

The Islands are volcanic in origin; Saya de Malha (35 mya) was the first of the Mascarene islands to rise out of the Indian Ocean due to the Réunion hotspot, followed by Nazareth Bank (some 2,000 yrs later), Soudan Bank and Cargados Carajos. The youngest islands to form were Mauritius (7–10 mya), the oldest of the existing islands, created along with the undersea Rodrigues ridge. The islands of Rodrigues and Réunion were created in the last two million years. Réunion is the largest of the islands (2,500 km²), followed by Mauritius (1,900 km²) and Rodrigues (110 km²). Eventually Saya de Malha, Nazareth and Soudan were completely submerged, Cargados Carajos remaining as a coral atoll. The Réunion hotspot was beginning to cool and Rodrigues came out as a tiny island. Had erosion not taken place, Cargados Carajos would have been a large volcanic island, and the Mascarenes would have been an archipelago of seven or more (counting Saya De Malha, Nazareth and Soudan) large, populated islands, rather than the three (Mauritius, Reunion, Rodrigues) that remain today.

Réunion is home to the highest peaks in the Mascarenes, the shield volcanoes Piton des Neiges (3,069 m) and Piton de la Fournaise (2,525 m). Piton de la Fournaise, on the southeastern corner of Réunion, is one of the most active volcanoes in the world, erupting last on 2 January 2010. Piton de la Petite Rivière Noire (828 m) is the highest peak on Mauritius, and the gentle hills of Rodrigues rise to only 390 m.

The Mascarene Plateau is an undersea plateau that extends approximately 2000 km, from the Seychelles to Réunion. The plateau covers an area of over 115,000 km² of shallow water, with depths ranging from 8 to 150 meters, plunging to 4000 m to the abyssal plain at its edges. The southern part of the plateau, including the Saya de Malha Bank, Nazareth Bank, Soudan Banks and Cargados Carajos Shoals (Saint Brandon) (then one large island), was formed by the Réunion hotspot. These were once volcanic islands, much like Mauritius and Réunion, which have now sunk or eroded to below sea level or, in the case of the Cargados Carajos, to low coral islands. The Saya de Malha Bank formed 35 million years ago, and the Nazareth Bank and the Cargados Carajos shoals after that. Limestone banks found on the plateau are the remnants of coral reefs, indicating that the plateau was a succession of islands. Some of the banks may have been islands as recently as 18,000–6,000 years ago, when sea levels were as much as 130 meters lower during the most recent ice age.