Ethiopia covers an area of 1,133,380 sq km (437,600 sq mi). The heart of the country is a high tableland, known as the Ethiopian Plateau, which covers more than half the total area of the country. The plateau is split diagonally in a northeastern to southwestern direction by the Great Rift Valley. Although the average elevation of the plateau is about 1,680 m (about 5,500 ft), it is cut by many rivers and deep valleys, some of which are 600 m (2,000 ft) below the level of the plateau. The area is capped by mountains, the highest of which is Ras Dashen (4,620 m/15,157 ft). These heights and indentations occur in northern Ethiopia, in the region surrounding Lake T’ana (the lake in which the Blue Nile rises).