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(also Eastern Cordillera of the Andes), mountain ranges which form the eastern fringes of the Andes mountain system.
In the Central Andean countries the term “Cordillera Oriental” has been applied to several mountain ranges, resulting in different readings on maps and in literature; it has been most firmly established as the name of mountains in the Andes of Colombia and Ecuador. Orographically the Cordillera Oriental is not a single mountain range, but structurally, along with the Cordillera Central, it does form a unified system of anticlinoria with Hercynian cores.
The Cordillera Oriental of Colombia extends from 1° 30’ to 9° N latitude as a large mountain range reaching an altitude of 5,493 m (Ritacuva). It declines sharply in the east to the level of the plains of the Orinoco River and the western edge of the Guiana Highlands and in the west to the basin of the Magdalena River. Extensive intermontane plains and hollows at altitudes of 2,500 to 3,500 m are characteristic of the central section (which is the broadest, with widths extending to 270 km). The range abruptly narrows and descends in the north (where it is called the Sierra de Perijá) and the south, where it becomes part of the Cordillera Central. It continues into Ecuador, where it is called the Cordillera Oriental or the Cordillera Real. In separate spurs and massifs the Cordillera Oriental of Ecuador descends in the east to the Amazon Basin; in front of the western slopes lie the high intermontane “basins,” or depressions. Extinct and active volcanoes that have formed peaks as high as 5,897 m (the Cotopaxi volcano) are built up along the fracture lines. In the south, between 4° and 6° S latitude, the Cordillera Oriental is not orographically expressed. Its structures continue further into the Cordillera Central of northern Peru, the Cordilleras of southeastern Peru, and the Cordillera Real of Bolivia.
In northern Peru the term Cordillera Oriental is also applied to the Sub-Andean Cordilleras, folded mountain ranges of moderate altitude that frame the western Amazon Basin (5°-10° S latitude) and the eastern chains of Bolivia, which border upon the plains of Beni-Mamore (15°-19° S latitude) at an elevation to 4,051 m.
Throughout their entire length the eastern slopes of the Cordillera Oriental face the wind (with precipitation ranging from 4,000 to 5,000 mm annually) and are deeply dissected by rivers and covered by evergreen forests (mountain tropical) with precisely delineated altitude zones. Only on the more arid northern and southern extremities and the western slopes are there mixed deciduous and evergreen forests and thin-forest areas. The snow line is located at an altitude of 4,400 to 5,000 m.
E. N. LUKASHOVA