mountains contain numerous glaciers, the largest of which, Fedchenko Glacier, covers more than and is the largest glacier in the world outside the polar regions. Because Tajikistan lies in an active seismic belt, severe earthquakes are common. Fergana Valley The Fergana Valley, the most densely populated region in Central Asia irrigated by the Syr Darya in its upper course, spreads across the north-eastern arm of Uzbekistan and Northern Tajikistan. This long valley, which lies between two mountain ranges — the Kuramin Range in the north and the Turkestan Range in the south, reaches its lowest elevation of at Khujand on the Syr Darya. Rivers bring rich soil deposits into the Fergana Valley from the surrounding mountains, creating a series of fertile oases that have long been prized for agriculture. Drainage In Tajikistan's dense river network, the largest rivers are the Syr Darya and the Amu Darya; the largest tributaries are the Vakhsh and the Kofarnihon, which form valleys from northeast to southwest across western Tajikistan. The Amu Darya carries more water than any other river in Central Asia. The upper course of the Amu Darya, called the Panj River, is long. The river's name changes at the confluence of the Panj, the Vakhsh, and the Kofarnihon rivers in far southwestern Tajikistan. The Vakhsh, called the Kyzyl-Suu ("red water" in Turkic languages) upstream in Kyrgyzstan and the Surkhob in its middle course in north-central Tajikistan, is the second largest river in southern Tajikistan after the Amu-Panj system. In the Soviet era, the Vakhsh was dammed at several points for irrigation and electric power generation, most notably at Norak (Nurek), east of Dushanbe, where one of the world's highest dams forms the Nurek Reservoir. Numerous factories also were built along the Vakhsh to draw upon its waters and potential for electric power generation. Due to the uneven distribution of water throughout Central Asia, the Soviets created a system in which Kyrgyzstan and Tajikistan provided water to Kazakhstan, Turkmenistan, and Uzbekistan in summer, and these three countries provided oil and gas to Kyrgyzstan and Tajikistan during winter. After the collapse of the USSR in 1991, this system fell apart and a new resource-sharing plan has yet to be put in place. According to research conducted by the International Crisis Group, this is due to corruption and lack of political will; failure to solve this issue could lead to irreversible regional destabilization. The two