Mauritania (Arabic: موريتانيا Mūrītāniyā), officially the Islamic Republic of Mauritania, is a country in northwest Africa. It is bordered by the Atlantic Ocean on the west, by Senegal on the southwest, by Mali on the east and southeast, by Algeria on the northeast, and by the Morocco-controlled Western Sahara on the northwest. It is named after the ancient Berber kingdom of Mauretania. The capital and largest city is Nouakchott, located on the Atlantic coast. The civilian government of Mauritania was overthrown on August 6, 2008, in a military coup d'état. At 397,929 square miles (1,030,700 km²)[15], Mauritania is the world's 29th-largest country (after Bolivia). It is comparable in size to Egypt. Mauritania is generally flat, its 1,030,700 square kilometers (397,850 sq mi) forming vast, arid plains broken by occasional ridges and clifflike outcroppings. A series of scarps face southwest, longitudinally bisecting these plains in the center of the country. The scarps also separate a series of sandstone plateaus, the highest of which is the Adrar Plateau, reaching an elevation of 500 meters (1,640 ft). Spring-fed oases lie at the foot of some of the scarps. Isolated peaks, often rich in minerals, rise above the plateaus; the smaller peaks are called guelbs and the larger ones kedias. The concentric Guelb er Richat (also known as the Richat Structure) is a prominent feature of the north-central region. Kediet Ijill, near the city of Zouîrât, has an elevation of 1,000 meters (3,280 ft) and is the highest peak. Approximately three quarters of Mauritania is desert or semidesert. As a result of extended, severe drought, the desert has been expanding since the mid-1960s. To the west, between the ocean and the plateaus, are alternating areas of clayey plains (regs) and sand dunes (ergs), some of which shift from place to place, gradually moved by high winds. The dunes generally increase in size and mobility toward the north.