At the heart of the formation of the African Rift
40 million years ago, immense quantities of lava spread through the Earth's crust, not in the form of eruptions but in a continuous flow lasting several million years. This resulted in the formation of a layer 2 to 4 km thick over a surface area of 700,000 km2. A second geological era began with the weakening of this layer, leading to the formation of fractures which, in turn, caused subsidence, of which the great African Rift Valley stretching from Ethiopia to Mozambique through Tanzania and Kenya is symptomatic. At the same time, the pressure generated by this massive collapse causes considerable volcanic masses to rise along these faults. In Ethiopia, these folds give rise to two mountain systems on either side of this north-east/south-west fissure, ranging from an average altitude of 2,000 m in the lowlands to over 4,000 m at the summits. Extensive volcanic activity, fuelled by these tectonic upheavals, and erosion caused by intense runoff and the formation of a network of watercourses, have shaped this characteristic landscape of high plateaus separated by incised valleys. This rugged topography, isolating one region from another, partly explains the high proportion of endemic species in Ethiopia's flora and fauna.
The mountainous highlands, an Ethiopian constant
They cover 58% of the country's surface area and occupy the regions of Wolo, Godjam and Gondar in the north, dominated by the Simien massif and its peak, Ras Dashen, culminating at 4,550 m. The result of intense volcanic activity some 40 million years ago, this chaos has been shaped by erosion over the centuries into an improbably steep relief of peaks, narrow valleys and tabular plateaus overlooking vertiginous gorges plunging 1,500 m.
In the center, the immense Choa plateau is home to the continent's highest capital, Addis Ababa. It is bordered to the south by the Arsi highlands and cut off from the Bale massif by the course of the Wabe Shebelle river. Located 400 km south-west of Addis Ababa, the Bale Mountains National Park covers an area of 2,470 km2, and boasts Ethiopia's second-highest peak: Mount Batu, at 4,307 m.
The mighty Blue Nile
One of the two sources of the Nile, the world's second largest river, is Lake Tana in the Ethiopian highlands. The Nile is called "blue" because its color is darker than that of the White Nile, which comes from Lake Victoria. Be sure to visit the Blue Nile Falls near Bahar Dar, especially after the rainy season when the water is abundant. The Ethiopian highlands, Africa's true water tower, provide 60% of the Nile's water, and up to 75% during the rainy season. From the time of the Pharaohs to the present day, the waters of the Blue Nile have always played a vital role in Egypt, which is why the planned construction of the Renaissance Dam in Ethiopia is opposed by both Sudan and Egypt downstream from the river. Nevertheless, as both countries have benefited greatly from the river in the past, a long-term solution is possible after tough negotiations. Ethiopia's basaltic plateaus are cut by the long river valleys and deep gorges of the major rivers they drain. In addition to the Blue Nile and its tributaries, these include the Tekele to the north, the Awash to the east and the Baro, Gojeb and Omo rivers to the west and south.
Lake Tana and the crater lakes
Lake Tana is a veritable inland sea, the largest body of water in Ethiopia, covering 3,500 km and including 37 islands, some of which are home to 14th-century churches and monasteries. Also irrigated by a string of seven large high-altitude lakes along the Rift Valley south of Addis Ababa and by crater lakes, the highlands concentrate most of the arable land between 1,000 and 2,500 m, on which the country's sedentary populations live. These are the main lakes where Addis Ababa's city-dwellers come to relax with their families and enjoy weekend water sports and animal watching. Lake Ziway is just 160 km from Addis Ababa and Lake Langano 215 km. It borders the Abijata and Shalla Lakes National Park, home to impressive flamingo and pelican populations. Thanks to the excellent quality of the road, it is even possible to reach Lake Awasa (273 km), whose shores are a veritable haven of peace.
The lowlands, desert zones
To the west, where the high plateaus gradually decline, a more humid climate allows agricultural activity along the Sudanese border, notably in the marshy Gambela region. The Omo valley in the south-west is one such area, and you can feel the heat immediately as you arrive at these low altitudes. The current drought, which has been raging for almost five years in the valley, is very worrying for the pastoral tribes who live there.
The east of the country is covered by the immense desert plains of Somali and Ogaden, and by the Danakil desert in the north-east. These desolate regions are home to nomadic Afar tribes who raise livestock or mine salt from the sweltering plains of the Dallol Depression, one of the planet's most spectacular geological curiosities for its Martian landscapes and hostile desert environment. This hotspot lies 136.8 m below sea level, on the border with Eritrea, on a mineral plateau created by a volcanic hotspot, considered to be the hottest on the planet. A palette of multicolored minerals creates the landscape. Small natural fountains of sulfuric acid escape from rock formations secreted by the soil. They resemble works of art saturated with colors: white, yellow, emerald green, red, brown... due to the presence of sulfides, salts, irons and numerous oxidized minerals.
