Danakil Depression Posted November 26, 2014

The Danakil Depression is a desert area in the Afar region of northeastern Ethiopia, north of the Great Rift Valley that is widely known locally as the Dallol depression.

This is both the hottest region on earth averaged year round and one of the most geologically active.

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 toAustralopithecus afarensis hominids dating back more than three million years ago.

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.

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.

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.

 

Spectacular colours at Dallol

 

Erta Ale

 

Acid pools and deposits of salt, sulphur and other minerals at Dallol

This is a vast expanse of blisteringly hot desert with lava flows and salt plains and lakes that lie below sea level. Active and extinct volcanoes lie along a south–north axis with the extremely salty Lake Afrera, at 120m below sea level, kept alive by the many thermal springs feeding it.

Dallol offers an opportunity to see the first signs of a new ocean basin forming. The Dallol volcano, the only volcanic crater below sea level on land, has remained dormant since 1926, as the seabed it will one day occupy gradually widens. South of Dallol, rectangular salt slabs are cut and transported up into the highlands in a near endless procession of camel caravans. The salt canyons south of Dallol Mountain are some of the most impressive geological features in the area. It looks like another planet because there are lots of colourful rocks in each metre of terrain. It looks like something out of a science fiction novel.

Dallol is at the northern-most extension of the Great Rift valley – the largest geographical feature in Africa (if you discount the erg and reg of the Sahara) and the only such feature easily discernible from the Moon by the first Americans to walk there. Because it’s below sea level it seems to trap all the heat. The most recent of its craters, Dallol, was formed during an eruption in 1926. Colourful hot brine springs and fumarole deposits are found in the Dallol area with some areas that are more than 116m (328ft) below sea level. There are hot yellow sulphur fields among the sparkling white salt beds. Heat isn’t the only thing people feel in the Dallol Depression. Alarming earth tremors are frequently felt. There are also several active volcanoes.

Erta Ale, an active shield volcano, is another impressive natural phenomenon. It is the most active volcano in Ethiopia. Erta Ale is 613m tall, with a lava lake, one of only five in the world, at the summit. It is the longest existing lava lake, present since 1906. Erta Ale, in whose crater lies the world’s only below sea level land volcano, has techni-colored landscapes, incredible mineral deposits. Sulphur lakes and bubbling sulphur springs are fascinating sights not to be missed.

The ghost town of Dallol, built from salt blocks and which almost straddles the Eritrean border to the east of the Tigrayan highlands, is officially listed as the hottest place on Earth, with an average annual temperature of 35 degrees Celsius and hottest daily temperatures topping 40°C year round. Much of this vast and practically unpopulated region lies below the driest and most tectonically active areas on the planet. The Danakil is an area of singular geological fascination. A strange lunar landscape studded with active volcanoes malodorous sulphur-caked hot springs. Solidified black lava flows. And vast salt encrusted basins. It is some measure of the Danakil’s geological activity that more than 30 active or dormant volcanoes roughly one quarter of the total as listed by the Smithsonian instituted global volcanism program. These volcanoes are all geological infants having formed over the past million years and with a great many taking their present shape within the last 10,000 years