Question: Pedro Mascarenhas was the first to explore the island atoll that comprises what landform?

full_context: Document 1: António de Noli: Antonio de Noli (born 1415 or possibly 1419;) was a 15th-century Genoese nobleman and navigator, and the first governor of the earliest European overseas colony in Subsaharan Africa. He discovered some of the Cape Verde islands on behalf of Henry the Navigator and he was made first Governor of Cape Verde by King Afonso V. In most history or geographic books, including ancient chronics, or encyclopedia, he is referred as "Antonio de Noli", as well as in official information by the Government of Cape Verde or in Cape Verde history articles or references. In Italy, he is known also as "Antonio da Noli" (see Note 21, below) or sometimes referred as "Antoniotto Usodimare".
Document 2: Islam in Seychelles: Islam in the Indian Ocean was established by Muslim sea merchants well before the European discovery of Seychelles. However, unlike in other island states including the Comoros and Maldives, there were no permanent inhabitants in Seychelles until the French settlement in 1770. Today, the Muslim population of the islands is reported to be only 1.1%, roughly 900 people. Many of its island neighbors in the southern Indian Ocean, including Comoros, the Maldives and Zanzibar, have a much larger Muslim influence because of their colonization by Muslims, before European colonization. Mauritius also has a much higher Muslim population due to the importation of labour from British India on a scale not seen in Seychelles. The government of Seychelles allows 15 minutes of religious broadcasting every Friday for the Muslim community.
Document 3: Middle Island, Tristan da Cunha: Middle Island is a small, uninhabited island in the South Atlantic Ocean, part of the Nightingale Islands. They are governed as part of Tristan da Cunha, an archipelago that is part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha. The island is part of the Nightingale Islands group Important Bird Area (IBA), identified as such by BirdLife International as a breeding site for seabirds and endemic landbirds. It is also known as Alex Island.
Document 4: Mascarene Islands: The Mascarene Islands ( ) or Mascarenhas Archipelago is a group of islands in the Indian Ocean east of Madagascar consisting of Mauritius, Réunion and Rodrigues. The collective title is derived from the Portuguese navigator Pedro Mascarenhas, who first visited them in the early sixteenth century. The islands share a common geologic origin in the volcanism of the Réunion hotspot beneath the Mascarene Plateau and form a distinct ecoregion with a unique flora and fauna.
Document 5: Tristan da Cunha: Tristan da Cunha ( ), colloquially Tristan, is the name of both a remote group of volcanic islands in the south Atlantic Ocean and the main island of that group. It is the most remote inhabited archipelago in the world, lying 2000 km from the nearest inhabited land, Saint Helena, and 2400 km from the nearest continental land, South Africa. It is 3360 km from South America. The territory consists of the main island, named Tristan da Cunha, which has a north–south length of 11.27 km and an area of 98 km2 , along with the smaller, uninhabited Nightingale Islands and the wildlife reserves of Inaccessible and Gough islands. As of January 2017, the main island has 262 permanent inhabitants. The other islands are uninhabited, except for the personnel of a weather station on Gough Island.
Document 6: Ascension Island: Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around 1600 km from the coast of Africa and 2250 km from the coast of Brazil, which is roughly midway between the horn of South America and Africa. It lies 7°56' South of the Equator. It is governed as part of the British Overseas Territory of Saint Helena, Ascension and Tristan da Cunha, of which the main island, Saint Helena, is around 1300 km to the southeast. The territory also includes the sparsely populated Tristan da Cunha archipelago, some 3730 km to the south, about halfway to the Antarctic Circle.
Document 7: Diogo Rodrigues: D. Diogo Rodrigues, D. Diogo Roiz ( 1490-1496; Lagos, Portugal – 21 April 1577; Colvá, Gôa) was a Portuguese explorer of the Indian Ocean who sailed as an ordinary helmsman under the command of D. Pedro Mascarenhas around Goa. They sailed from the Cape of Good Hope eastward into little-known waters of the newly discovered route to Gôa. It was after him that the island of Rodrigues was\is named between 4 and 9 February 1528 after discovering it during his only return journey from Gôa via Cochin (left on 15 January 1528) to Portugal, following which he rose to the rank of a knight "(cavaleiro)". He then returned to Gôa and made a mark in the history of the Portuguese empire in the subcontinent around the mid 16th century.
Document 8: Saint Helena, Ascension and Tristan da Cunha: Saint Helena, Ascension and Tristan da Cunha is a British Overseas Territory located in the South Atlantic and consisting of the island of Saint Helena, Ascension Island and the archipelago of Tristan da Cunha.
Document 9: Geography of Seychelles: The Seychelles is a small island nation located in the Indian Ocean northeast of Madagascar and about 1600 km east of Kenya. Seychelles lies between approximately 4ºS and 10ºS and 46ºE and 54ºE. The nation is an archipelago of 155 tropical islands, some granite and some coral. the majority of which are small and uninhabited. The landmass is only 459 km, but the islands are spread over an Exclusive Economic Zone of 1,374,000 km. About 90 percent of the population of 90,000 live on Mahé, 9 percent on Praslin and La Digue. Around a third of the land area is the island of Mahé and a further third the atoll of Aldabra.
Document 10: Pedro Álvares Cabral: Pedro Álvares Cabral (] ] ; c. 1467 or 1468 – c. 1520) was a Portuguese nobleman, military commander, navigator and explorer regarded as the discoverer of Brazil. Cabral conducted the first substantial exploration of the northeast coast of South America and claimed it for Portugal. While details of Cabral's early life are unclear, it is known that he came from a minor noble family and received a good education. He was appointed to head an expedition to India in 1500, following Vasco da Gama's newly opened route around Africa. The object of the undertaking was to return with valuable spices and to establish trade relations in India—bypassing the monopoly on the spice trade then in the hands of Arab, Turkish and Italian merchants. Although the previous expedition of Vasco da Gama to India, on its sea route, recorded signs of land west of the southern Atlantic Ocean (in 1497), Cabral is regarded as the first captain who ever touched four continents, leading the first expedition that united Europe, Africa, America, and Asia.
Document 11: Abel Tasman: Abel Janszoon Tasman (] ; 1603 – 10 October 1659) was a Dutch seafarer, explorer, and merchant, best known for his voyages of 1642 and 1644 in the service of the Dutch East India Company (VOC). He was the first known European explorer to reach the islands of Van Diemen's Land (now Tasmania) and New Zealand, and to sight the Fiji islands.
Document 12: Réunion: Réunion (French: "La Réunion" , ] ; previously "Île Bourbon") is an island and region of France in the Indian Ocean, east of Madagascar and 175 km southwest of Mauritius. s of 2016 , it had a population of 850,996. It is the most prosperous island in the Indian Ocean, having the highest GDP per capita in the region.
Document 13: Pedro Mascarenhas: Dom Pedro Mascarenhas (1470 – 16 June 1555) was a Portuguese explorer and colonial administrator. He was the first European to discover the island of Diego Garcia in the Indian Ocean in 1512. He also encountered the Indian Ocean island of Mauritius in 1512, although he may not have been the first Portuguese explorer to do so; earlier expeditions by Diogo Dias and Afonso de Albuquerque along with Diogo Fernandes Pereira may have encountered the islands. In 1528 explorer Diogo Rodrigues (after whom the island of Rodrigues is named) named the islands of Réunion, Mauritius, and Rodrigues the Mascarene Islands, after Mascarenhas.
Document 14: Mauritius: Mauritius ( or ; French: "Maurice" ), officially the Republic of Mauritius (French: "République de Maurice" ), is an island nation in the Indian Ocean about 2000 km off the southeast coast of the African continent. The country includes the islands of Mauritius and Rodrigues, 560 km east of Mauritius, and the outer islands (Agaléga, St. Brandon and two disputed territories). The islands of Mauritius and Rodrigues form part of the Mascarene Islands, along with nearby Réunion, a French overseas department. The area of the country is 2,040 km2 . The capital and largest city is Port Louis.
Document 15: Diego Garcia: Diego Garcia is an atoll just south of the equator in the central Indian Ocean, and the largest of 60 small islands comprising the Chagos Archipelago. It was settled by the French in the 1790s and was transferred to British rule after the Napoleonic Wars. It was one of the "Dependencies" of the British Colony of Mauritius until it was detached for inclusion in the newly created British Indian Ocean Territory (BIOT) in 1965. Between 1968 and 1973, the population was forcibly removed by the United Kingdom and the United States (in order to establish an American base) through intimidation of locals and denying the return of any who left the island. Many were deported to Mauritius and Seychelles, following which the United States built a large naval and military base on Diego Garcia, which has been in continuous operation ever since. s of 2015 , Diego Garcia is the only inhabited island of the BIOT; the population is composed of military personnel and supporting contractors.
ground_truth: Chagos Archipelago