The Andes salt lake reflects the history of the Earth's climate and history

Covering the entire landscape is a thick salt shell on the surface, which accumulates over the millennia due to the dual impact of low rainfall and high humidity in the tropical environment in a very high area compared to the sea. These extended desert deserts are also called salt lakes. They formed under the arid climate of the Central Andes over several million years. There are hundreds of such deserts, spread across Bolivia, Chile and Argentina.

The chemical composition of this salt layer is very complex and varied, with many high value properties for industrial production. Salt and elements contained in this class include: Bo, KaCO¬¬3, Li, and NaCO3. Where does this chemical composition come from? To find the answer, an IRD geologist and his colleagues studied the history of formation and provided evidence of events leading to today's chemical composition.

They surveyed and analyzed 80 salt lakes, scattered over 1,000 kilometers of the Andes in the territory of Bolivia and northern Chile. Most of these lakes have not been studied scientifically and thoroughly.

Lake salt second generation

The data from hundreds of samples were used and analyzed to recreate the process of forming lakes today. It can be divided into two groups of salt and the main element based on their origin: the group formed from volcanic rock (Li, Bo) and the group from the ancient salt lakes (Cl, sulfate). During a time when volcanoes were active, ancient salt lakes were covered by volcanic material.Therefore, groundwater under salt lakes contains many chemical elements derived from rocky mountains decaying.

At the same time, ancient salt lakes were dissolved, forming groundwater blocks with characteristics from salty vapor to extreme salinity. Water seeps from volcanic rocks and from salt lakes merging together, forming new basins. And this is the precursor to today's salt lakes. Now, the ancient salt lakes buried under the ground have completely disappeared.

The Andes deserts are mined due to the abundance of salt in the chemical composition. (Photo: IRD / Denis Wirrmann)

Two origins with many possibilities

The team also tested the evaporation models and changes in the sand density of water in the slots and compared these test results with the current measured density. The above models do not take into account geochemical interactions with sediment layers and the decomposition of saline salts formed earlier. They are based only on the chemical composition of flows flowing into salt lakes. The scientists found that there was a difference between the results from the model and the measured value, especially in Bolivia.

These differences are caused by several factors such as the increase of groundwater, interaction with sediment layers, the dissolution of saline salts that have formed before, etc. . These differences prove too The past has been the phenomenon that researchers today do not know. For example, in Bolivia, the analysis of the results shows a big difference: some salt lakes, which should be high in NaCO3, are actually neutral or even slightly acidic with high sulfate content.This unexpected component is the result of corrosive sulfur ore, related to volcanic activity in the surrounding areas.

Salt lakes are an invaluable source of water for the Andes people as well as large-scale mining. Therefore, it is important to identify the characteristics and potential assessment of water resources to prepare the basis for examining the impact of industrial activities on this particular and sensitive ecosystem.

Besides the impact of water pollution, the mining industry also uses a large amount of fresh and brackish water . These activities take up a large volume as well as alter the chemical composition of the groundwater that nourishes the salt lakes. At the same time, they take away the source of drinking water of indigenous inhabitants. This is a big problem for the central Andes and the Pacific side.

Refer:
1. Risacher et al. Origin of Salts and Brine Evolution of Bolivian and Chilean Ho. Aquatic Geochemistry, 2009; 15 (1-2): 123 DOI: 10.1007 / s10498-008-9056-x
2. Risacher F., Alonso H., Salazar C. The origin of brines and Chilean salts: a hydrochemical review.Earth Science Reviews, 63 (3-4), 2003 DOI: 10.1016 / S0012-8252 (03) 00037-0