The Usoi Dam is a natural

landslide dam A landslide dam or barrier lake is the natural damming of a river by some kind of landslide, such as a debris flow, rock avalanche or volcanic eruption. If the damming landslide is caused by an earthquake, it may also be called a quake lake. Some ...

along the Murghab River in

Tajikistan Tajikistan, officially the Republic of Tajikistan, is a landlocked country in Central Asia. Dushanbe is the capital city, capital and most populous city. Tajikistan borders Afghanistan to the Afghanistan–Tajikistan border, south, Uzbekistan to ...

. At high, it is the tallest dam in the world, either natural or man-made. The dam was created on 18 February 1911, when the 7.4- M_s Sarez earthquake caused a massive

landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...

that blocked the flow of the river. The dam is formed of approximately of rock dislodged from the steeply sloped river valley of the Murghab, which cuts from east to west through the high and rough

Pamir Mountains The Pamir Mountains are a Mountain range, range of mountains between Central Asia and South Asia. They are located at a junction with other notable mountains, namely the Tian Shan, Karakoram, Kunlun Mountains, Kunlun, Hindu Kush and the Himalaya ...

. It is named after the village of Usoi, which was completely buried by the 1911 landslide. The dam rises to a height of from the original valley floor. The basin formed by Usoi Dam now holds

Sarez Lake Sarez Lake ( ) is a lake in Rushon District of Gorno-Badakhshan province, Tajikistan. Its length is about , its depth about a few hundred meters, its water surface elevation about above sea level, and volume of water over . The mountains around ...

, a -long lake holding of water. Water does not flow over the top of the dam, which would quickly cause it to erode away; instead, water seeps out of the base of the dam at a rate which approximately matches the rate of inflow, maintaining the lake at a relatively constant level. The level thus only rises an average of 20 cm per year. The flow averages about 45 cubic meters per second, with an annual variation of 35-80 cubic meters per second and dissipates about 250 megawatts. Geologists are concerned that the Usoi Dam may become unstable during future large-magnitude earthquakes, which are relatively common in the seismically active Pamirs, and might collapse due to

liquefaction In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of t ...

or subsequent landslides during such an event. Collapse of the dam would unleash a locally catastrophic flood. The Murghab's river valley tends to be relatively narrow and steep. This would focus and maintain any flood's destructive power as it swept through the valley of the

Murghob District Murghob District () is a district in Tajikistan, occupying the eastern two-thirds of the Gorno-Badakhshan Autonomous Region (GBAO). The area of Murghob District is 37,300 km2, covering 26 percent of Tajikistan's soil, but only 0.17% of its popula ...

. The dam wall survived a localised 7.2 magnitude earthquake, the 2015 Tajikistan earthquake, on 7 December 2015, with no visible signs of deterioration.

References

External links

Map of the Usoi Dam – Sarez Lake, Scale 1:110'000Map of Gorno-Badakhshan region of Tajikistan
{{Webarchive, url=https://web.archive.org/web/20081219170307/http://www.pamirs.org/images/maps/gbaorm.gif , date=2008-12-19

Dams in Tajikistan Lakes of Tajikistan Gorno-Badakhshan Autonomous Region Landslides in Asia Natural disasters in Tajikistan Landslide-dammed lakes 1910s landslides 1911 natural disasters