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Ankarana Special Reserve in northern Madagascar was created in 1956. It is a small, partially vegetated plateau composed of 150-million-year-old middle Jurassic limestone. With an average annual rainfall of about ,〔 the underlying rocks are susceptible to erosion, thereby producing caves and underground rivers—a karst topography. The rugged relief and the dense vegetation have helped protect the region from human intrusion. The plateau slopes gently to the east, but on the west it ends abrubtly in the "Wall of Ankarana", a sheer cliff that extends north to south, and rises as high as . To the south, the limestone mass breaks up into separate spires known as ''tower karst''. In the center of the plateau, seismic activity and eons of rainfall have dissolved the limestone away in deep gorges, and sometimes redeposited it in ribbons of flowstone. In places where the calcific upper layers have been completely eroded, the harder base rock has been etched into channels and ridges known as ''tsingy''.〔 The largest sinkhole in the Ankarana karst region, Mangily sinkhole, measures up to 700 meters across and 140 meters deep with a volume of 25 million cubic meters. The area is sacred to the Antankarana people, who have historically taken refuge from encroaching enemy armies in its caves and other natural rock shelters. ==Exploration== Beginning in the 1960s, expatriate Frenchman Jean Duflos (who married locally and changed his name to Jean Radofilao) did a huge amount of exploration of the cave systems and subterranean rivers of the Massif, much of it on his own or with visiting speleologists. A total of about of cave passages within the massif have been mapped. One of the most accessible caves, La Grotte d'Andrafiabe, alone comprises at least of horizonatal passages. Indeed the Massif contains the longest cave systems in Madagascar, and probably in the whole of Africa.〔http://www-sop.inria.fr/agos/sis/DB/countries.html〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ankarana Reserve」の詳細全文を読む スポンサード リンク
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