The caravans move at dawn, before the heat becomes an assault: long files of camels and donkeys stepping out across a plain so white it hurts to look at. At Lake Asale, in the far north of Ethiopia, Afar workers crack the crust with poles and axes, lever up slabs of salt and trim them into standard blocks by hand, as their ancestors did for centuries when the bars — called amole — circulated as money in the Ethiopian highlands. Each camel is loaded with slabs and turned towards the mountains, on a trek of days to the trading town of Berhale and the markets of the Tigray highlands beyond. The men do this work in one of the lowest, hottest places on the planet: the Danakil Depression.
The Danakil, part of the wider Afar Triangle spanning north-eastern Ethiopia, Eritrea and Djibouti, lies well below sea level — its lowest reaches are roughly 125 metres down. It is routinely called the hottest inhabited place on Earth, and the claim rests on a specific record: at the settlement of Dallol, measurements taken in the 1960s produced an average annual temperature of about 34.5°C. Not a heatwave peak — the average, day and night, winter and summer. Daytime highs run well into the forties for much of the year, and rainfall rarely amounts to more than 100 to 200 millimetres. There is no cool season to wait for. The salt itself records the region's drowned past: the Red Sea has broken into this basin and evaporated away repeatedly, and each flooding left another layer, building beds of salt hundreds of metres thick beneath the plain.
Where three plates tear apart
The Depression exists because the ground beneath it is being unmade. The Afar Triangle sits at a triple junction where the Nubian, Somali and Arabian tectonic plates are all pulling away from one another; the crust here is stretched, thinned and sinking. The Red Sea and the Gulf of Aden are the older, flooded arms of the same rifting, and geologists expect that the sea will eventually break in and drown the Danakil too — it has flooded before, which is why such deep beds of salt are there to mine. In the meantime the thin crust leaks heat everywhere. Erta Ale, a shield volcano in the depression whose name is often translated as smoking mountain — and which guides cheerfully bill as the gateway to hell — holds one of the world's very few persistent lava lakes. And at Dallol itself, hot brine forced up through the salt erupts into a hydrothermal field of springs and terraces in colours that look faked: acid greens, sulphur yellows, rust oranges, with pools that are near-boiling, salt-saturated and in places about as acidic as battery acid.
People live and work here anyway, and have for a very long time. The Afar have herded, traded and mined this landscape for centuries, and the salt trade endures, though lorries now take a growing share of the load the camels once carried. It is one of the great commutes on Earth: the caravan track drops some two and a half kilometres of altitude between the highland market towns and the salt flats, and the trade swells in the cooler months, when the plain fills with camel trains. Outsiders have fared less well. In the early twentieth century an Italian company mined potash at Dallol, hauling it to the Eritrean coast on a purpose-built railway; the venture was abandoned within decades, leaving Dallol a ghost settlement of salt-block ruins, regularly described as one of the remotest inhabited places anywhere.
The cradle next door
The same rifting that makes the Afar hellish also made it one of palaeoanthropology's great treasure chests: the sinking basin buries bones quickly in sediment, and later faulting slices the layers open for anyone walking the gullies. In 1974, at Hadar in the Afar region, Donald Johanson's team found the 3.2-million-year-old partial skeleton of Australopithecus afarensis known as Lucy — named, famously, after the Beatles song Lucy in the Sky with Diamonds, which was playing in camp on the night of the discovery. More recently, astrobiologists have taken an interest in Dallol as an analogue for early Mars, and some studies have argued that a few of its hottest, most acidic pools may be genuinely sterile — among the rare places on the Earth's surface where even microbes cannot make a living.
That is the Danakil's strange double role: a nursery of humanity on the edge of habitability, where our ancestors got their start — and where, in a few luminous brine pools, life itself finally gives up.
Quiz nuggets
- The Danakil Depression lies roughly 125 metres below sea level in the Afar Triangle.
- Dallol recorded an average annual temperature of about 34.5°C in the 1960s — the usual basis for calling it the hottest inhabited place on Earth.
- The Afar Triangle is a triple junction where the Nubian, Somali and Arabian plates pull apart.
- Erta Ale volcano holds one of the world's few persistent lava lakes.
- Lucy, the 3.2-million-year-old Australopithecus afarensis skeleton, was found at Hadar in the Afar region in 1974.