Mauritania is generally flat, its 1,030,700 square kilometers 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. 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 is a prominent feature of the north-central region. Kediet Ijill, near the city of Zouīrāt, has an elevation of 1,000 meters and is the highest peak.
Approximately three-fourths of Mauritania is desert or semidesert. As a result of extended, severe drought, the desert has been expanding since the mid-1960s. The plateaus gradually descend toward the northeast to the barren El Djouf, or "Empty Quarter," a vast region of large sand dunes that merges into the Sahara Desert. 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.
The climate is characterized by extremes in temperature and by meager and irregular rainfall. Annual temperature variations are small, although diurnal variations can be extreme. The harmattan, a hot dry wind, blows from the Sahara throughout most of the year and is the prevailing wind, except along the narrow coastal strip, which is influenced by oceanic trade winds. During the short rainy season (hivernage), from July to September, average annual precipitation varies from 500 to 600 millimeters in the far south to 0 to 100 millimeters in the northern two-thirds of the country. Belts of natural vegetation, corresponding to the rainfall pattern, extend from east to west and range from traces of tropical forest along the Senegal River to brush and savanna in the southeast. Only sandy desert is found in the center and north of the country.
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