The Afar Triangle is an uninhabited, arid depression at the southern end of the Red Sea. This area comprises parts of Eritrea, Ethiopia as well as Djibouti and is approximately four times the size of Switzerland. In the west, it borders on the Ethiopian Plateau and in the south on the Somali Plateau.
Big parts of the Afar Triangle lie more than 100 metres below sea level. Earthquakes repeatedly rip the surface open, volcanoes erupt and hot springs bubble in the fissures.
The cause of the turbulence below the surface: magma, burning-hot molten rock, is injected from the Earth’s mantle upwards and spreads under the Earth crust like a gigantic mushroom cap. Geologists call it a mantle plume. It is usually several hundred kilometres in diameter. This ‘hot mushroom’ presses so strongly against the Earth crust that the latter stretches, ruptures and caves in.
It is a unique spot on our planet – the climate is very hot and the landscape is bizarre, as if from another planet.
Lac Assal is situated more or less in the centre of the Afar Triangle. It is a salt lake and with 35% salinity, it is one of the saltiest stretches of water on Earth. Its water is ten times saltier than that of the Earth’s oceans and that of the Dead Sea. The Afar people inhabiting parts of Ethiopia and Djibouti preoccupy themselves with extracting salt on the lakeshores and transporting it to the remote towns and settlements.
The water level of Lake Assal lies 152 metres below sea level. This saline lake stretches along a fault zone in the Earth’s crust, where hot lava presses out of the fissures and cools off to form a blanket of rough black rock.
In the Ghoubbet al Kharab, a gulf near the capital of Djibouti, turquoise-coloured seawater washes round the dark lava fields and volcano craters.
There are plenty of such small volcanic cones to be found in the Afar Triangle. They lie mainly along rifts. Next to them, there are also big volcanoes, which look completely different ……
… for instance, Dalla Filla with its steep slopes. Clouds of gas billowing from the edge of its crater show that the volcano is still active and merely lies dormant – it is far from extinct.
Contrary to that, the nameless volcano has been extinct for a long time. Weathering and erosion have ablated it. After a rare rainfall in this desert region, water has collected in its crater and the scraggy shrubs on its slopes sport new leaves.
The most spectacular and best-known volcano in the Afar Triangle is Erta Ale with a lake of molten lava in its crater.
The level of the lava lake fluctuates – it falls and rises all the time. Sometimes the molten rock overflows the edge of the crater, solidifies and creates a new layer on the caldera floor. In December 2003, when this photo was taken, the magma level was about 80 metres below the volcanic vent.
A thin black layer formed on top of the scorching lava like a skin on hot milk. The molten rock below bubbled and moved like the waves of a surging sea. Repeatedly, the dark layer lacerated and burning lava fountains shot 10 or 20 metres up in the air. The hot air soaring through the crater was burning hot.
(More info and photos on the topic in the blog story Lava Lake Watching)
About 80 kilometres north of Erta Ale volcano, near the border to Eritrea, lies the geothermal area of Dallol. Water, which once came down as rain over the Ethiopian Highlands, trickled away and flowed as ground water into the Afar Depression hundreds of kilometres away, where it oozes out of the ground, hot and laden with minerals. It creates one of the most bizarre landscapes the world.
As soon as the water cools down at the surface and comes into contact with the air, the minerals, which it flushed out from the underground water source, dissolve. A thick white crust of salt hems the pools of hot, clear, light green shimmering water. Presumably iron and sulfur compounds colour the crust in patches of orange, yellow and brown.
In some places, water bubbling from the ground builds up salt towers. As soon as it dries out, the salt towers become brown and start crumbling.
Additionally to salt lakes, volcanoes, hot springs areas and lacerated volcanic deserts, there are also areas such as Sac Allol in the Afar Triangle. Geologists refer to it as landscape with strike slip faults. These monumental steps are also signs of the enormous pressure coming from the great depths below, which causes the stretching of the Earth’s surface.
What is the future of the Afar Triangle? Geologists are of the opinion that the lowland plains could cave in, the Red Sea could stretch into the Afar Triangle and a new ocean could emerge.
Should the pressure subside gradually, the deep ground in the Afar Triangle would calm down and Africa would stay as it is today.