Friday, March 5, 2021

The Rainbow Mountain

The Ausangate Mountain of the Peruvian Andes also known as the rainbow mountain is one of the most breathtaking geological features in the world. The mountain is awash with colours from red to turquoise to green to gold and is even thought to be holy. To local citizens who bring offerings to the geological wonder it is a place of daily worship.

Located approximately 100 km outside of Cusco and with an elevation of 6,384 meters the Peruvian rainbow mountain truly is one of Earth’s most beautiful and remote treasures that only a few get to witness.

But just how did this mountain form?

The Andes, the range to which the rainbow mountain belongs, formed along the western edge of the South American continent due to subduction. The Nazca plate subducted under the South American plate resulting in mountain building and the uplift of the mountain range. This also initiated volcanism and the introduction of rare mineralogy to the Andes.

Uplift and tectonically driven crustal shortening has tilted the sedimentary layers on exposing colourfully stripped stratigraphic intervals. The reason these Peruvian mountains exhibit such varied colours is due to weathering and their unique mineralogy.

The different colouration is due to different environmental conditions and mineralogy when the sediment was originally deposited and subsequently diagenetically altered. Red colouration of sedimentary layers often indicates iron oxide rust as a trace mineral. Introduction of goethite or oxidized limonite will introduce brownish colouration to sandstones. The bright yellow colouration could be due to iron sulphide as trace minerals. The varying shades of green colour depend on chlorite in different diagenetic states and concentrations.

As you gaze at this breathtaking landscape you are looking at millions of years of Earth’s history encapsulated in technicoloured strata.

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