The vast area covered by the Arab World encompasses wide and diverse geographical features ranging from deserts and shrublands to Mediterranean forests and snow-capped mountain ranges. Deserts reign in most of northern Africa where the Sahara exists, the world's hottest desert where some of the sand dunes can reach 180 metres (590 ft) in height. The Arabian Peninsula is mainly covered by a range of deserts: the Nefud in the north, which is a stony desert; the Rub' Al-Khali or Great Arabian Desert in the south, and between them, the Dahna desert. In contrast, the Arab World boasts some of the highest mountain ranges in both Africa and Asia. The Atlas Mountains rise from the northern Sahara to peak of 4,167 m before cascading east towards the Mediterranean and west towards the Atlantic Ocean. The Hijaz mountains rise parallel to the Red Sea on the western edge of the Arabian Peninsula, separating the coastline from the inland deserts. Mountains like the Mount Lebanon and the Taurus Mountains mark the edges of the Levant, providing heavy rainfall and snowfall, thus nurturing the areas' forest landscapes.