Lake Tauca is a former lake in the Altiplano of Bolivia. It is also known as Lake Pocoyu for its constituent lakes: Lake Poopó, Salar de Coipasa and Salar de Uyuni. At high water levels, the lake spread across the southern Altiplano between the Eastern and Western Cordilleras, flooding the basins that now hold Lake Poopó and the Uyuni and Coipasa salars. Published area estimates range from about 48,000 to 80,000 square kilometres (19,000 to 31,000 sq mi). Water levels varied, possibly reaching about 3,800 metres (12,500 ft) above sea level. It was a saline lake. The lake received water from Lake Titicaca, although estimates of Titicaca's contribution vary widely. In any case, Tauca was large enough to influence local climate and to depress the underlying terrain under its own weight. Diatoms, plants and animals lived in the lake, sometimes forming reef-like carbonate knolls. The duration of Lake Tauca's existence is uncertain. Research published in 2011 suggested that lake levels began rising around 18,500 BP and reached their main highstand around 16,000–14,500 years ago. Around 14,200 years ago, lake levels fell, then rose again and persisted until about 11,500 years ago. Some researchers suggest that the final phase may have continued until about 8,500 BP. When the lake dried—possibly during the Bølling–Allerød oscillation—it left the salt deposits of Salar de Uyuni. Lake Tauca is one of several ancient lakes which formed in the Altiplano. Lake Tauca was one of several named Altiplano palaeolakes (including Escara, Ouki, Salinas, Minchin, Inca Huasi and Sajsi), alongside repeated highstands of Lake Titicaca. How these named lake phases relate to one another is debated. Sajsi is often treated as part of the Tauca system, and Tauca itself is frequently divided into an earlier Ticaña phase and a later Coipasa phase. Lake Tauca formed when the Altiplano became colder and wetter, likely because shifts in the Intertropical Convergence Zone (ITCZ) strengthened easterly moisture transport. Early explanations emphasised glacial meltwater, but melt alone would not have provided enough water to fill the lake. Glaciers advanced alongside the lake, leaving clear evidence at Cerro Azanaques and Tunupa. Elsewhere in South America, water levels and glaciers also expanded during the Lake Tauca phase.
Description
Overview Lake Tauca formed on the Altiplano, a 1,000 by 200 kilometres (620 mi × 120 mi) wide high plateau in the central Andes, the world's longest mountain chain. It lies about 3,800 to 4,000 metres (12,500 to 13,100 ft) metres above sea level between Bolivia's Eastern and Western Cordilleras. The Altiplano is underlain by a Paleozoic basement, which is covered by Cretaceous to Pleistocene sediments, which form its surface. Uplift of the Altiplano began in the Miocene, and it became a closed basin during the late Pliocene-early Pleistocene. The Andean Central Volcanic Zone and the Altiplano–Puna volcanic complex are in the Cordillera Occidental. The Cordillera Real is glaciated, while the southern Altiplano peaks are ice-free owing to the dry climate. As of 2018, temperatures at 3,800 metres (12,500 ft) altitude range between 6.3–8.5 °C (43.3–47.3 °F). Climate varies strongly from north to south: mean temperatures and precipitation drop from 15 °C (59 °F) and 700 millimetres (28 in) in the north to about 7 °C (45 °F) and 100 millimetres (3.9 in) in the southern Lípez area, reflecting the direction of prevailing winds and the topography. The climate is arid, evaporation rates throughout the Altiplano exceed 1,500 millimetres per year (59 in/year). A larger daily than seasonal temperature range, strong winds and high insolation are other aspects of the Altiplano climate. Much of the water balance in the present-day Altiplano-Atacama area is maintained by groundwater flow. Most precipitation is recorded between October and April, when easterly winds associated with the South American Summer Monsoon transport humidity from the Amazon. They are the principal source of precipitation in the Altiplano, and responsible for its increase in a south-north direction. The climate of the Altiplano is usually dry when westerly winds prevail, but frontal systems can bring snowfall, mainly in winter but sometimes in summer. Its location at the edge of the monsoon belt makes the Altiplano climate sensitive to climate oscillations, such as the El Niño-Southern Oscillation. Lake Titicaca is a large lake in the northern Altiplano and covers a surface area of 8,560 square kilometres (3,310 sq mi); it usually drains through the Rio Desaguadero to Lake Poopó. The Salar de Uyuni, at an altitude of 3,653 metres (11,985 ft) with an area of 10,000 square kilometres (3,900 sq mi), and the Salar de Coipasa, covering 2,500 square kilometres (970 sq mi) at an altitude of 3,656 metres (11,995 ft), are large salt pans. Lake Titicaca and the southern salt flats are two separate water basins; a sill at 3,703 metres (12,149 ft) altitude separates Poopó from Coipasa. Another sill, only a few metres high, at 3,672 metres (12,047 ft) altitude separates Coipasa from Uyuni. Channels, for example the Rio Laca Jahuira between Poopó and Coipasa, indicate the past connections between lakes; water levels exceeding 3,700 metres (12,100 ft) result in the formation of a waterbody spanning Poopó, Coipasa and Uyuni. Sometimes during wet years, like 1986, the salt flats fill with water and become partially connected.
Geography
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