Other than the low, rolling hills of Turkish Thrace, the fertile river valleys that open to the Aegean Sea, the warm plains of Antalya and Adana on the Mediterranean, and the narrow littoral along the Black Sea, the country is wrinkled by rugged mountain ranges that surround and intersect the high, semiarid Anatolian plateau. Average elevations range from 600 m (2,000 ft) above sea level in the west to over 1,800 m (6,000 ft) amid the wild eastern highlands. The highest point is Mount Ararat (Büyük Agri Dagi, 5,166 m/16,949 ft), which rises just within Turkey at the intersection of the Turkish, Armenian, and Iranian frontiers. There are over 100 peaks with elevations of 3,000 m (10,000 ft) or more. Other than the Tigris and Euphrates, which have their sources in eastern Anatolia, rivers are relatively small. Because the watersheds of these streams are semibarren slopes, the seasonal variations in flow are very great. The largest lake is Lake Van (3,675 sq km/1,419 sq mi); the other major lake is Lake Tuz, whose water has a salinity level so high that it serves as a commercial source of salt. Turkey's 7,200 km (5,474 mi) of coastline provide few good natural harbors.
Most of Turkey lies within an earthquake zone, and recurrent tremors are recorded. On 29–30 March 1970, more than 1,000 earthquakes were felt in the Gediz region of western Turkey, killing 1,086 persons. The record destructive earthquake, however, was that of 29 December 1939—near Erzincan—which killed 30,000 persons.