The Semien Mountains are the highest parts of the Ethiopian Plateau (more than 2,000 meters; or 6,560 feet). They are surrounded by a steep, ragged escarpment (step), with dramatic vertical cliffs, pinnacles, and rock spires. Included in the range is the highest point in Ethiopia, Ras Dashen at 4,533 meters (14,926 feet). The plateau and surrounding areas are made up of basalt rock from massive, flood-like eruptions of lava; these flood basalts are probably more than 3,000 meters thick.
The lavas erupted quickly (in about one million years) 31 million years ago, as the tectonic plate carrying Ethiopia passed above what is known as the Afar hotspot, a localized spot of intense heat or magma production that is not at a tectonic plate boundary. As the tectonic plate passed over the hotspot, the general region of Ethiopia rose in elevation. The uplift encouraged the erosion that cut the highly dramatic canyons that ring the plateau.
Although the plateau lies in the latitude of the Sahara–Arabia deserts, its high altitude makes for a cool, wet climate. In fact, the Semien Mountains are one of the few places in Africa to regularly receive snow, and they receive plentiful rainfall (more than 1,280 millimeters, or 55 inches). The moderate climate is shown by light green vegetation on the mountains, compared with the brown canyons, which are hot and dry. The green tinge on the biggest escarpment (trending across the bottom third of the image) is also vegetation, showing that this part of the escarpment also receives more rain than other parts of the escarpment wall. A major canyon cuts the flatter plateau surface (image center), with several more surrounding the plateau. These canyons are hot because they reach low altitudes, more than 2,000 meters below the plateau surface.
The Semien Mountains National Park has been declared a World Heritage Site by the United Nations Educational, Scientific and Cultural Organization for its rugged beauty. In addition, several extremely rare species are found here, such as the Gelada baboon, which has a thick coat to protect against the cold; the critically endangered Walia ibex, which has long, heavy scimitar-like horns; and the Ethiopian wolf, also known as the Semien jackal, which is one of the rarest, and perhaps most endangered canid on Earth.
Astronaut photograph ISS016-E-10784 was acquired on November 16, 2007, with a Kodak 760C digital camera fitted with a 180 mm lens, and is provided by the ISS Crew Earth Observations experiment. The image was taken by the Expedition 16 crew, and it is provided by the Image Science & Analysis Laboratory, Johnson Space Center. The image in this article has been cropped and enhanced to improve contrast. Lens artifacts have been removed. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of the Earth. Caption by M. Caption by M. Justin Wilkinson, NASA-JSC.
