A Tectonic Collision Zone
The Rakhine Yoma mountain range is a direct and active consequence of plate tectonics. It exists because the Indian Plate is moving north and sliding under the Burma microplate. This process, called subduction, is the same geological engine that formed the Himalayas. The range is an accretionary prism, a massive pile of Cenozoic flysch sediments scraped off the top of the Indian Plate and folded upwards. The pile of rock and sediment, which began forming in the Eocene epoch (roughly 55 million years ago), now sits on a metamorphic basement.
The mountain arc extends for about 950 kilometers (600 miles) from north to south. Deep beneath the surface, the subducting Indian Plate dips eastward at an angle that steepens with depth, from about 18-25 degrees to as much as 45 degrees. The immense pressure and friction at this plate boundary periodically release, causing frequent earthquakes. The 2004 Indian Ocean earthquake, a magnitude 9.1 event, was caused by a massive slip along this subduction zone, vertically shifting the seafloor by up to 5 meters. The range itself is a continuation of the same geological structure that emerges from the sea to form the Andaman and Nicobar Islands.
A Barrier of Biodiversity
Stretching along Myanmar's western coast, the Rakhine Yoma creates a significant climatic barrier. The mountains intercept moisture-laden winds from the Bay of Bengal during the southwest monsoon, forcing the air to rise and cool. This orographic effect results in staggering amounts of rainfall on the western slopes, with some areas receiving over 4,000 mm annually. The eastern slopes lie in a rain shadow, contributing to the much drier conditions of central Myanmar's "Dry Zone".
This dramatic climatic gradient produces a variety of distinct ecosystems. The range is part of the Chin Hills-Arakan Yoma montane forests ecoregion, which covers about 29,700 square kilometers. Below 1,000 meters, forests are characterized by species of Bauhinia, Lagerstroemia, and Ficus. Above this elevation, oaks (Quercus) and chestnuts (Castanopsis) become dominant. The highest peak, Nat Ma Taung (formerly Mount Victoria), reaches 3,094 meters (10,151 feet). Its upper elevations support temperate flora, including various species of rhododendron, that are relics from the last Ice Age, forming an alpine "sky island".
The forests are habitat for a wide array of wildlife. They support one of Myanmar's important Asian elephant populations and host the world's largest population of the Western Hoolock gibbon. Other resident mammals include the clouded leopard, sun bear, and gaur. The range is also important for birdlife, with several endemic species like the white-browed nuthatch (Sitta victoriae). One of the most famous residents is the critically endangered Arakan forest turtle (Heosemys depressa), a species once thought to be extinct until it was rediscovered in 1994.