Horn of Africa covered the Simien and Bale Mountains but melted at the beginning of the Holocene. The mountains descend in a huge escarpment to the Red Sea and more steadily to the Indian Ocean. Socotra is a small island in the Indian Ocean off the coast of Somalia. Its size is 3,600 km (1,390 sq mi) and it is a territory of Yemen. The lowlands of the Horn are generally arid in spite of their proximity to the equator. This is because the winds of the tropical monsoons that give seasonal rains to the Sahel and the Sudan blow from the west.
Horn of Africa single landmass around 18 million years ago, before the Gulf of Aden rifted and separated the Horn region from the Arabian Peninsula. The Somali Plate is bounded on the west by the East African Rift, which stretches south from the triple junction in the Afar Depression, and an undersea continuation of the rift extending southward offshore. The northern boundary is the Aden Ridge along the coast of Saudi Arabia. The eastern boundary is the Central Indian Ridge, the northern portion of which is also known as the Carlsberg Ridge. The southern boundary is the Southwest Indian Ridge. Extensive glaciers once