Ethiopian Highlands

The Ethiopian Highlands, often called the Abyssinian Highlands, are a rugged mountain mass stretching across Ethiopia and into Eritrea in Northeast Africa. This region is the largest continuous area of its elevation on the continent, with almost no land below 1,500 meters and peaks reaching up to 4,550 meters. Its height and expanse have earned it the nickname "Roof of Africa," and Ethiopia is the only country in the area with such a high-altitude landscape.

Geology

The highlands are split diagonally by the Great East African Rift System, which runs from Syria to Mozambique through the East African Great Lakes. Most of the highlands lie in central and northern Ethiopia, with the Eritrean Highlands forming the northernmost part. The Ethiopia-Yemen Continental Flood Basalts are a geological feature shared between the Horn of Africa and the highlands of Upper Yemen, reflecting the cultural, historical, and genetic connections between these regions on opposite sides of the Red Sea.

History

In the southern highlands once stood the Kingdom of Kaffa, a medieval and early modern state. From this mountainous, forested land, the coffee plant was exported to the Arabian Peninsula.

The soil here is very fertile, capable of producing three harvests a year, and the word "coffee" traces back to the name Kaffa. To the north, in the Amhara region, genetic adaptations to the high-altitude conditions of low oxygen and low atmospheric pressure have been found among the Amhara people. These include variations in genes linked to hemoglobin function (rs10803083), circadian rhythm and hypoxia response (BHLHE41), and oxygen homeostasis (EGNL1), adaptations that may have developed within the last 5,000 years.

Physical geography

The Main Ethiopian Rift divides the highlands into northwestern and southeastern sections. The northwestern part, known as the Abyssinian Massif, includes the Semien Mountains, home to Simien Mountains National Park. Its highest point, Ras Dashen at 4,550 meters, is Ethiopia’s tallest peak. Lake Tana, the source of the Blue Nile, is also in this northwestern region.

The southeastern section is called the Harar Massif, bounded by the Rift Valley fault line to the west, the Ogaden Lowlands to the east, and the Elkerie and Borena Lowlands to the south. Its highest peaks are in the Bale Zone of Oromia Region, where the Bale Mountains—also a national park—are nearly as tall as the Semien range. This area is the main source of the Wabishebelle and Genalle (Juba) rivers, with peaks over 4,000 meters, including Mount Tullu Demtu (4,337 meters), Ethiopia’s second-highest independent mountain, and Mount Batu (4,307 meters). Most of Ethiopia’s major cities, including the capital Addis Ababa and historic capitals like Gondar and Axum, sit at elevations between 2,000 and 2,500 meters.

Geologically, the Ethiopian Highlands began rising 75 million years ago as magma from the Earth’s mantle uplifted a broad dome of ancient rocks from the Arabian-Nubian Shield. The opening of the Great Rift Valley later split this dome into three parts; the mountains of the southern Arabian Peninsula are geologically part of the original highlands, separated by the rifting that created the Red Sea and Gulf of Aden and divided Africa from Arabia. Around 30 million years ago, a flood basalt plateau formed, piling up layers of voluminous fissure-fed basaltic lava flows. Most flows were tholeiitic, with a thin layer of alkali basalts and minor amounts of felsic volcanic rocks like rhyolite.

In the later stages, large explosive caldera-forming eruptions occurred. The highlands were eventually bisected by the Great Rift Valley as the African continental crust pulled apart, giving rise to large alkaline basalt shield volcanoes starting about 30–31 million years ago. The northern highlands contain four discernible planation surfaces, the oldest dating back to the Ordovician Period and the youngest formed in the Cenozoic, partly covered by the Ethiopia-Yemen Continental Flood Basalts. Unlike much of Africa, these surfaces in northern Ethiopia are not considered pediplains or etchplains.

Climate

Climate in Ethiopia is shaped mainly by altitude and latitude. Though the country lies within the tropics, where every location has overhead sun twice a year, the highlands’ elevation gives them non-tropical temperatures. The predominant climate here is alpine, while tropical conditions are found in the lowlands at the country’s edges.

Because the highlands lift Ethiopia close to the equator, the country enjoys an unexpectedly temperate climate. These mountains also catch the monsoon rains from the Indian Ocean, creating a rainy season from June to mid-September. These heavy rains cause the Nile to flood in summer, a phenomenon that puzzled ancient Greeks, who were used to dry summers in the Mediterranean.

The Ethiopian Highlands share a similar flora and fauna with other mountainous regions of Africa.