Saya de Malha Bank

The Saya de Malha Bank lies northeast of Madagascar, southeast of Seychelles, and north of Nazareth Bank, the Cargados Carajos Shoals, and the island of Mauritius, and currently falls mostly under international waters. The closest land is tiny Agaléga (one of the Outer Islands of Mauritius), some 300 km (190 mi) further west, followed by the southern Seychellois island of Coëtivy, some 400 km (250 mi) northwest. Mauritius administers the whole Saya de Malha Bank as a portion of it lies within its exclusive economic zone.

The bank covers an area of 40,808 km² (15,756 sq mi),[1] and is composed of two separate structures, the smaller North Bank (also called Ritchie Bank), and the huge South Bank. If the South Bank were recognized as a submerged atoll structure, it would be the largest of the world, almost three times the size of the Great Chagos Bank, commonly considered the largest atoll structure of the world. Even smaller North Bank would be one of the largest atolls worldwide. The North Bank and the South Bank appear to have different origins, since they are separated by a fault. The South Bank and the Great Chagos Bank were one single feature until about 64 to 69 million years ago, when an ocean ridge opened between them and started pushing them apart.[2]

The Saya de Malha Bank consists of a series of narrow shoals, with depths from 17 to 29 m (56 to 95 ft) on the rim. They are arranged in a semicircular manner, around a space, the former lagoon, about 73 m (240 ft) deep, which slopes on the Southeast. Some areas of the bank are shallow, less than 10 m (33 ft) below the surface. The shallowest sites known are Poydenot Rock, at a depth of 8 m (26 ft), and an unnamed site 145 km (90 mi) further northwest, with a depth of 7 m (23 ft). The banks are covered with sea grass interspersed with small coral reefs. Due to its remote location, the bank is among the least-studied shallow marine ecoregions on the planet. The banks are a breeding ground for humpback whales and blue whales.

The bank was formed 35 million years ago by the Réunion hotspot, and is composed of basaltic basal rock overlain with limestone. The limestone banks found on the plateau are the remnants of coral reefs. Millions of years ago, the bank was one or more mountainous volcanic islands, like present-day Mauritius and Réunion, which subsequently sank below the waves. Some of the banks may have been low islands as recently as 18,000-6,000 years ago, when sea levels were up to 130 m (430 ft) lower during the most recent ice age.

The bank was named by Portuguese explorers 500 years ago, who encountered the bank on the voyage between the Cape of Good Hope and India. After traversing miles of deep blue Indian Ocean, they found themselves sailing above a shallow area of the bank, covered with swaying green seagrass.

The first scientific survey of the bank was undertaken by Captain Robert Moresby of the Royal Navy in 1838. Moresby previously surveyed the Laccadives, the Red Sea, the Maldives and the Chagos Banks. Due to Moresby's ill health, the Saya de Malha bank was his last survey in a long and brilliant career exploring and charting the archipelagos and reefs of the Indian Ocean.[3]

• Hawkins Bank
• Nazareth Bank
• Robert Moresby
• Soudan Banks

• Saya de Malha Bank (Lighthouse Foundation)