Hydrology, Alveoli, And SALT DECAY!

The Salar de Uyuni is considered a closed draining basin. This means, unlike the hydrology examples we took a look at in class, the water that falls here, stays here. Water can only escape by evaporation and minor infiltration. This low drainage density (of practically zero) causes the salt flats to fill up with water when rainfall occurs. The salt on top dries and creates a hard concrete crust, sometimes many feet thick, yet underneath is undrained salt water, if one is able to break through the surface. 

This thin crust revels the salt water lurking underneath, since the water cannot drain in this closed basin!

This water will be here until it evaporates. 

When the surface of the Salar dries up it does so in hexagon shaped patterns. It may look a lot like clay desiccation cracking, but it is not the same.This phenomena is quite puzzling to me, but I know this unique pattern must be attributed to the high concentration of salt and the closed draining basin of the Salar. With further investigation, I believe this can be attributed to the crystallization of the salt and the heating and cooling that occurs as the salt flats transition from the rainy to hot season.

The salt flats of Bolivia experience salt weathering, which is a physical or mechanical decay process. In the nearby town of Colchani, residents use stones to hold down the roofs of houses because nails cannot stand the decay effects of the salt. 

On the Salar de Uyuni there are a series of 'islands', thought to be leftover remnants of ancient volcanos. The rock structures on the islands show great examples of salt decay, in the form of tiny holes, also known as alveoli and larger holes of tafoni. This YouTube video, gives a panoramic view of the island and showcases the alveoli and tafoni on the island:

 https://www.youtube.com/watch?v=8neLFQmjhYg 

Take a look! And see the effects of salt weathering on the island rocks. 

 The video also shows the stark contrast between the little vegetation growing on the island and the total lack of vegetation on the salt flats themselves. This is due to the infertility of the salt flats. The high salt content creates a very alkaline environment and this excess of salt, or salinization, makes plant growth nearly impossible. Salinization points to little precipitation and hotter temperatures, so it is very fitting that the only vegetation on the island is the hardy cacti and small desert shrubs.

Man standing on one of the islands, deep in thought about the surrounding tafoni.

Works Cited

• http://dialogo-americas.com/en_GB/articles/saii/features/entertainment/2012/10/24/feature-02
• http://www.reddit.com/r/askscience/comments/1zw794/why_do_desertsdried_up_lakes_form_polygon/
• http://www.jon.hk/2012/02/bolivia-salt-flats-of-uyuni/
• http://upload.wikimedia.org/wikipedia/commons/9/9b/Hexagons,_Salar_de_Uyuni,_Bolivia_(2086104060).jpg
• Redwood, Stewart. Salt of the Earth. South American Explorer. 

Images

• http://gqtrippin.com/wp-content/uploads/2013/03/DSC_0382.jpg
• http://www.jon.hk/2012/02/bolivia-salt-flats-of-uyuni/
• http://upload.wikimedia.org/wikipedia/commons/9/9b/Hexagons,_Salar_de_Uyuni,_Bolivia_(2086104060).jpg

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