The paleolake of Cancosa is a

former lake A former is an object, such as a template, Gauge block, gauge or cutting Die (manufacturing), die, which is used to form something such as a boat's Hull (watercraft), hull. Typically, a former gives shape to a structure that may have complex curv ...

Cancosa Cancosa is a Chilean commune. It is a highland in Aymara town in the Tarapacá Region. Cancosa is slightly on the slopes of the Sillajhuay volcano, near the border by Bolivia. According to the Chile National Archive the town was founded by the M ...

, Chile. The existence of the lake was inferred on the basis of limnic sediments in the area, which lies in the Tarapacá Region of Chile. Presently, the area is occupied by a basin at about altitude within the Western Cordillera and surrounded by high mountains, such as Cerro Porquesa and

Sillajhuay Sillajhuay (also known as Sillajguay or Alto Toroni) is a volcano on the border between Bolivia and Chile. It is part of a volcanic chain that stretches across the border between Bolivia and Chile and forms a mountain massif that is in part cover ...

. The area is arid (precipitation less than ) owing to the

rain shadow A rain shadow is an area of significantly reduced rainfall behind a mountainous region, on the side facing away from prevailing winds, known as its leeward side. Evaporated moisture from water bodies (such as oceans and large lakes) is carrie ...

of the Andes and the influence of the

South Pacific High The South Pacific High is a semi-permanent subtropical anticyclone located in the southeast Pacific Ocean. The area of high atmospheric pressure and the presence of the Humboldt Current in the underlying ocean make the west coast of Peru and no ...

; most precipitation falls during summer. The lake has been reconstructed on the basis of data obtained by analyzing its sediments and the biological traits of diatoms found therein. Water levels varied through its history, with the lake occasionally becoming

bog A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg; a ...

-like. Most of the time, the lake reached depths of only a few meters, and it was a calm water body.

Radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was dev ...

shows that shallowing occurred in the middle Holocene between 4,700 - 3,700 BP, coinciding with the mid-Holocene lowstand of Lake Titicaca. Afterwards lake levels increased until 3,000 BP; subsequently a lake level drop becomes noticeable by 1,000 BP and about 700 years before present the lake finally drained to the

Salar de Coipasa __NOTOC__ Lago Coipasa or Salar de Coipasa is a lake in Sabaya Province, Oruro Department, Bolivia. At an elevation of 3657 m, its surface area is 806 km². It is on the western part of Altiplano, 20 km north of Salar de Uyuni and south ...

, for reasons unknown although it is possible that the Rio Cancosa at that point breached the lake basin. Presently, a few

salt lake A salt lake or saline lake is a landlocked body of water that has a concentration of salts (typically sodium chloride) and other dissolved minerals significantly higher than most lakes (often defined as at least three grams of salt per litre). ...

s occur in the Cancosa basin. The Cancosa River, which forms at the confluence of the Saccaya River and Ocacucho River, drains the basin today. These rivers cut into the lake sediments and are the only perennial rivers today in the area. The Cancosa River ultimately drains into the

. The lake featured a diverse

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

flora, with over 98 taxa represented. Among the most common taxa found in lake deposits are ''

Achnanthes lanceolata ''Achnanthes'' is a genus of diatoms belonging to the family Achnanthaceae. The genus was described in 1822 by Jean Baptiste Bory de Saint-Vincent. The genus has cosmopolitan distribution In biogeography, cosmopolitan distribution is the ...

'', '' Fragilaria capucina'' and '' Naviculadicta chilensis''. Most diatoms identified are periphytic and there are no planktonic species. The lake was sometimes eutrophic and sometimes not, which may reflect volcanic influence on its waters.

References

Bibliography

* * {{Altiplano lakes and paleolakes Former lakes of South America Lakes of Tarapacá Region Geology of Tarapacá Region Holocene South America