In the east heights of more than 900 metres (3,000 ft) are attained in the Ennedi and Ouaddaï plateaus. The greatest elevations are reached in the Tibesti Mountains in the north, with a maximum height of 3,415 metres (11,204 ft) at Emi Koussi. The northern half of the republic lies in the Sahara. The Bodélé Depression is a low region in the southern Sahara that is surrounded by basalt mountain ridges. Winds flow through this region and lift dust. The dust from this region supplies over half of the dust to Amazon rainforests.