Ashgabat in 1948. The Krasnovodsk and Üstýurt plateaus are the prominent topographical features of northwestern Turkmenistan. A dominant feature of the republic's landscape is the Garagum Desert (also known as Karakum), which occupies about 350,000 square kilometers. Shifting winds create desert mountains that range from two to twenty meters in height and may be several kilometers in length. Chains of such structures are common, as are steep elevations and smooth, concrete-like clay deposits formed by the rapid evaporation of flood waters in the same area for a number of years. Large marshy salt flats, formed by capillary action in the soil, exist in many depressions, including the Garaşor, which occupies 1,500 square kilometers in the northwest. The Sandykly Desert west of the Amu Darya river is the southernmost extremity of the Qizilqum Desert, most of which lies in Uzbekistan to the northeast. Climate Turkmenistan has a cold desert climate that is severely continental. Summers are long (from May through September), hot, and dry, while winters generally are mild and dry, although occasionally cold and damp in the north. Most precipitation falls between January and May; precipitation is slight throughout the country, with annual averages ranging from in the Kopet Dag to in the northwest. The capital, Ashgabat, close to the Iranian border in south-central Turkmenistan, averages of rainfall annually. Average annual temperatures range from in Ashgabat to in Daşoguz, on the Uzbek border in north-central Turkmenistan. The almost constant winds are northerly, northeasterly, or westerly. On 28 July 1983, Repetek Biosphere State Reserve, south of Türkmenabat, recorded a temperature of , which is the highest temperature to have ever been recorded in Turkmenistan. Examples Hydrological conditions Almost 80% of the territory of Turkmenistan lacks a constant source of surface water flow. Its main rivers are located only in the southern and eastern peripheries; a few smaller rivers on the northern slopes of the Kopetdag are diverted entirely to irrigation. The most important river is the Amu Darya, which has a total length of 2,540 km from its farthest tributary, making it the longest river in Central Asia. The Amu Darya flows across northeastern Turkmenistan, thence eastward to form the southern borders of Uzbekistan and Tajikistan. Damming and irrigation uses of the Amu Darya have had severe environmental effects on the Aral Sea, into which the river flows. The river's average annual flow is 1,940 cubic meters per second. Other major