Pastos Grandes

Pastos Grandes has erupted a number of ignimbrites through its history, some of which exceeded a volume of 1,000 cubic kilometres (240 cu mi).

After the ignimbrite phase, the lava domes of the Cerro Chascon-Runtu Jarita complex were erupted close to the caldera and along faults.

[3] The specific area of Pastos Grandes is remote and poorly accessible,[4] the existence of the caldera was first established by satellite imagery.

[5] The region has been heavily affected by volcanism, including large ignimbrites and stratovolcanoes extending into Chile.

Volcanic rocks include andesite, dacite and rhyodacite with the former dominating in the Chilean stratovolcanoes and the latter in the ignimbrites.

[9] Pastos Grandes is a nested caldera which underwent repeated collapse in the past,[10] most likely along defined sectors of its rim.

[2] Cerro Pastos Grandes is 5,802 metres (19,035 ft) high and shows traces of a sector collapse.

[17] Plutonic rocks linked to Pastos Grandes were erupted from the Chascon-Runtu Jarita vents 94,000 - 85,000 years ago.

This mud freezes during the winter months to a certain depth and cryoturbation has formed polygonal structures as well as large cracks in the crust on its surface.

[3] Surfaces of open water are concentrated on the eastern edge of the salt pan, in its very centre and isolated areas on the western side, these all form an intricated network[33] of interconnected ponds especially in the western half of the salt pan.

[42] It is unclear what drives its formation as the climate at Pastos Grandes is similar to that of other salt lakes without such platforms[31] but it may be a consequence of carbon dioxide degassing under the salar.

[45] All these cave formations encountered at Pastos Grandes are caused by the precipitation of calcite from oversaturated waters at the surface.

[47] Animal species found within the lakes include amphipods, elmids and leeches in freshwater and by Cricotopus in saltwater.

[48] Additional animals are Euplanaria dorotocephala, Chironomidae, Corixidae, Cyclopoida, Ephydridae, Harpacticoida, Orchestidae, Ostracoda and Tipulidae species.

[49][50] Similar but different animal species have been found in other local lakes, indicating that they are largely separate systems.

[51] The animal flora of such Altiplano lakes is not very diverse, probably due to their relative youth and the harsh and often highly variable climates of the past in the region.