The whole Afar Depression is a plate tectonic triple junction where the spreading submarine ridges that formed the Red Sea and the Gulf of Aden emerge on land and meet the East African Rift. The Afar Depression is one of two places on Earth where a mid-ocean ridge can be studied on land, the other being Iceland. At present, the Afar is slowly being pulled apart at a rate of 1-2cm per year. The floor of the Afar Depression is composed mostly of basaltic lava. The Afar Depression and Triple Junction also mark the location of a mantle plume, a great uprising of the earth’s mantle that melts to yield basalt.
Near the southern end of the Red Sea an immense, more or less triangular, depression descends far below sea level – some points near the ghost town of Dallol are nearly 120m below sea level). Known as the Danakil/Dallol Depression, the northern part is extremely hot and dry and an extension of the Great Rift Valley. In this seemingly inhospitable area live the nomadic Afar people who number about 3 million and largely disregard the notional borders between Ethiopia, Eritrea, Djibouti and Somaliland.
This is the land of “Ardi” (Ardipithecus ramidus) and “Lucy” (Australopithecus afarensis) – hominids which have been proposed as among our first putative ancestors. In June 2010, the oldest direct evidence of stone tool manufacture was found in this region and attributed to Australopithecus afarensis hominids dating back more than three million years ago.
This place, which used to be part of the Red Sea, has kilometres of salt deposits. In some places the salt deposits are about 5km (3 mi) thick. Below many salt lakes are substantial sources of volcanic heat which causes hot water to rise through layers of salt and deposit anhydrites. Minerals also get dissolved and are deposited near the springs, and form shapes very much reminiscent (but smaller than) hornitos on basaltic lava flows. Sulphur, other minerals and possibly Thermopylae bacteria cause spectacular colours.