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18-481: The Mascarene Plateau is a submarine plateau in the Indian Ocean , north and east of Madagascar . The plateau extends approximately 2,000 km (1,200 mi), from Seychelles in the north to Réunion in the south. The plateau covers an area of over 115,000 km (44,000 sq mi) of shallow water, with depths ranging from 8–150 m (30–490 ft), plunging to 4,000 m (13,000 ft) to

36-537: A better record of large-scale volcanic eruptions throughout Earth's history. This "docking" also means that oceanic plateaus are important contributors to the growth of continental crust. Their formations often had a dramatic impact on global climate, such as the most recent plateaus formed, the three, large, Cretaceous oceanic plateaus in the Pacific and Indian Ocean: Ontong Java, Kerguelen, and Caribbean. Geologists believe that igneous oceanic plateaus may well represent

54-415: A ratio intermediate between continental and oceanic crust, although they are more mafic than felsic. However, when a plate carrying oceanic crust subducts under a plate carrying an igneous oceanic plateau, the volcanism which erupts on the plateau as the oceanic crust heats up on its descent into the mantle erupts material which is more felsic than the material which makes up the plateau. This represents

72-456: A stage in the development of continental crust as they are generally less dense than oceanic crust while still being denser than normal continental crust. Density differences in crustal material largely arise from different ratios of various elements, especially silicon . Continental crust has the highest amount of silicon (such rock is called felsic ). Oceanic crust has a smaller amount of silicon ( mafic rock). Igneous oceanic plateaus have

90-544: A step toward creating crust which is increasingly continental in character, being less dense and more buoyant. If an igneous oceanic plateau is subducted underneath another one, or under existing continental crust, the eruptions produced thereby produce material that is yet more felsic, and so on through geologic time. Volcanic island Geologically, a volcanic island is an island of volcanic origin. The term high island can be used to distinguish such islands from low islands , which are formed from sedimentation or

108-471: Is one of the most active volcanoes in the world. Oceanic plateau 3°03′S 160°23′E  /  3.050°S 160.383°E  / -3.050; 160.383 An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. There are 184 oceanic plateaus in the world, covering an area of 18,486,600 km (7,137,700 sq mi) or about 5.11% of

126-921: The Falkland Plateau , Lord Howe Rise , and parts of Kerguelen , Seychelles , and Arctic ridges. Plateaus formed by large igneous provinces were formed by the equivalent of continental flood basalts such as the Deccan Traps in India and the Snake River Plain in the United States. In contrast to continental flood basalts, most igneous oceanic plateaus erupt through young and thin (6–7 km (3.7–4.3 mi)) mafic or ultra-mafic crust and are therefore uncontaminated by felsic crust and representative for their mantle sources. These plateaus often rise 2–3 km (1.2–1.9 mi) above

144-925: The abyssal plain at its edges. It is the second-largest oceanic plateau in the Indian Ocean after the Kerguelen Plateau . The northern part of the Mascarene Plateau includes the Agaléga Islands and the Seychelles Islands . The southern part of the Mascarene Plateau includes Hawkins Bank , the Mascarene Islands , Nazareth Bank , the Saya de Malha Bank , and the Soudan Banks . The Mascarene Islands are

162-564: The islands of the South Pacific Ocean , where low islands are found on the fringing reefs that surround most volcanic islands. Volcanic islands normally rise above a hotspot or subduction zone . Volcanic islands usually range in size between 1 and 104 square kilometres (0.4 and 40 sq mi). Islands above a certain size usually have fresh groundwater , while low islands often do not, so volcanic islands are more likely to be habitable. Many volcanic islands emerge from

180-465: The uplifting of coral reefs (which have often formed on sunken volcanos). There are a number of volcanic islands that rise no more than 1 metre (3 ft 3 in) above sea level , often classified as islets or rocks, while some low islands, such as Banaba , Henderson Island , Makatea , Nauru , and Niue , rise over 50 metres (160 ft) above sea level. The two types of islands are often found in proximity to each other, especially among

198-548: The Cargados Carajos shoals formed later. Limestone banks found on the plateau are the remnants of coral reefs , indicating that the plateau was once 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 up to 130 meters lower during the most recent ice age . Mauritius formed 8–10 million years ago, and Rodrigues and Réunion formed around two million years ago. Piton de la Fournaise volcano on Réunion

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216-574: The ancient supercontinent of Gondwana . The granite is topped with deposits of limestone and basalt . The basalt deposits in the Seychelles are from the Deccan Traps eruption, which occurred in the central part of the Indian subcontinent 66 million years ago , at the end of the Cretaceous period. The southern part of the Mascarene Plateau, also known as Southern Mascarene Plateau (SMP),

234-443: The deep abyss of the ocean, and feature rough or mountainous landscapes in their interiors and a diverse array of summit elevations. Researchers have observed that the island will often be covered by dense tropical forest. These limit settlement on the interior of many islands, forcing communities to develop along the coast. Larger islands may have rivers, resulting in flood hazards. Rivers deliver sediment downstream, which can dominate

252-480: The mountainous islands of the Cargados Carajos Shoals , Mauritius , Réunion , and Rodrigues . The Indian subcontinent was at one time next to the east coast of Seychelles, but seafloor spreading has moved the landmass to its current position, where it has collided and fused with the continent of Asia . The northern part of the Mascarene Plateau is formed of granite , and is a fragment of

270-581: The oceans. The South Pacific region around Australia and New Zealand contains the greatest number of oceanic plateaus (see map). Oceanic plateaus produced by large igneous provinces are often associated with hotspots , mantle plumes , and volcanic islands — such as Iceland, Hawaii, Cape Verde, and Kerguelen. The three largest plateaus, the Caribbean , Ontong Java , and Mid-Pacific Mountains , are located on thermal swells . Other oceanic plateaus, however, are made of rifted continental crust, for example

288-473: The shape of the coast and contribute to erosion. Tall volcanic islands are often surrounded by protective fringing or barrier reefs, creating lagoons. The unique geological and geographical characteristics of volcanic islands make them prone to many natural hazards, which are expected to worsen due to climate change . These include volcanic eruptions, earthquakes, tsunamis, landslides, and severe weather events like hurricanes or typhoons. Studies have highlighted

306-414: The surrounding ocean floor and are more buoyant than oceanic crust. They therefore tend to withstand subduction, more-so when thick and when reaching subduction zones shortly after their formations. As a consequence, they tend to "dock" to continental margins and be preserved as accreted terranes . Such terranes are often better preserved than the exposed parts of continental flood basalts and are therefore

324-649: Was formed by the Réunion volcanic hotspot along with the Chagos–Laccadive Ridge . The banks and shoals of the southern part of the Mascarene plateau 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

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