The parallel mountain ranges of the Tell or Maritime Atlas, comprising coastal massifs and northern inland ranges, and the Saharan Atlas divide Algeria into three basic longitudinal zones running generally east–west: the Mediterranean zone or Tell; the High Plateaus, including the regions of Great and Small Kabilia; and the Sahara Desert, accounting for at least 80% of Algeria's total land area. About half of Algeria is 900 m (3,000 ft) or more above sea level, and about 70% of the area is from 760 to 1,680 m (2,500 to 5,500 ft) in elevation. The highest point is Mount Tahat (3,003 m/9,852 ft), in the Ahaggar Range of the Sahara.
Only the main rivers of the Tell have water all year round, and even then the summer flow is small. None of the rivers are navigable. The mountainous areas of the High Plateaus are poorly watered; most of the rivers and streams (oueds) flow irregularly, since they depend for water upon an erratic rainfall. In the High Plateaus are many salt marshes and dry or shallow salt lakes (sebkhas or shotts). Farther south, the land becomes increasingly arid, merging into the completely dry desert.
Algeria lies on the African Tectonic Plate. Northwestern Algeria is a seismologically active area. Earthquakes on 10 October 1980 in a rural area southwest of Algiers left over 2,500 persons dead and almost 100,000 homeless.