Salar de Gorbea

Salar de Gorbea is a salt flat just south of the border between the Antofagasta and Atacama regions, within Chile but close to the border with Argentina.

The salt flat
Salar de Gorbea lies at the margin of the Puna and the Atacama Desert. It covers a surface area of 32 km2 and lies at an elevation of 3944 m, in an area where access is difficult. The salt flat has an irregular shape, a square-shaped southern basin with an irregularly shaped bay to the northeast. Salar de Gorbea features both salty sediments, a salt crust and water-filled ponds. The crust is about a metre thick, contains liquid brine and is largely covered by gypsum crystals. A gypsum deposit has formed at the northeastern margin of Salar de Gorbea. Despite the name, the salt crusts are not flat, but have a topography of about 2 m formed by e.g. wind-formed dunes.

At some points, saltwater crops out in depressions, forming seven lakes up to a metre deep with various colours, which contain gypsum crystals The ponds may have formed through the dissolution of salt and through wind-driven erosion. Their water is, unusual for the region, acidic, probably due to the high availability of sulfur which yields sulfuric acid and the exhaustion of the buffer capacity of the rock. The total water surface is about 0.5 km2. There are diffuse springs at the margins of Salar de Gorbea. Water reaches Salar de Gorbea mostly from the east in the form of small creeks. A 15 km long tributary joins Salar de Gorbea from the south.

Chemistry
Salar de Gorbea contains gypsum as the main salt, crystals are up to 30 cm long. Thenardite occurs at its southern reaches and there is amorphous silica, clay, epsomite and limonite. Other rare salt types form efflorescences at the margins of the salar. There is evidence that the salts in Salar de Gorbea are presently dissolving. The Salar de Gorbea environment has been described as a potential Mars analogue.

Biology
The bacterial population of the salar has been investigated to determine their taxonomy, research has yielded new species and genera. The ponds often contain microbial mats. There are also diatoms and green algae, which sometimes get encased in the gypsum crystals. Its flora is poorly studied and probably consists entirely of halophyte plants at its margins. There are not many animals in the region, and none have been reported from the salar waters.

Catchment
The salt flat is nourished by a small watershed with an area of 336 km2. It is delimited to the east by the Cordon del Azufre, Cerro Bayo Complex and Cerro Atalaya, by Cerro los Patitos to the south and the Sierra de Gorbea to the west; other basins in the area are Salar de Pajonales, Salar de la Azufrera to the west and Salar Ignorado to the south. The rocks in the basin are entirely volcanic, mostly of Pleistocene age, many volcanoes are eroded and there is no evidence of recent activity except for a steam eruption at Cerro Bayo in 2007. Some of the volcanoes feature raw sulfur deposits.

Climate
Salar de Gorbea has an extreme climate characterized by dry air, high aridity, strong winds, high insolation and extreme temperature fluctuations between day and night and between seasons. Annual precipitation only reaches 140 mm and the annual mean temperature is about -1 C; winter temperatures can drop to -30 C. During the late Pleistocene, the climate of the Altiplano was wetter but there is no evidence of former shorelines although the gypsum crust was partially eroded during Holocene wet periods. Strong winds blow in the area, forming large dust devils on the salar that can reportedly transport gravel. Snow accumulates on the mountains at Salar de Gorbea and their meltwater is a major water source for the salar.