One of the most magnificent geologic features in the world is the Ausangate Mountain of the Peruvian Andes. The mountain is striped with colors ranging from turquoise to lavender to maroon and gold. However, this “painted mountain” is notoriously difficult to find and get to, requiring several days of hiking to reach its peak deep within the Andes by way of Cusco.
The painted Ausangate mountain is also considered to be holy and believed to be the deity of Cusco by local Peruvians. It is a site of daily worship and offerings by local citizens. Every year thousands of Quechua pilgrims visit the Ausangate Mountain for the Star Snow festival which takes place a week before the Corpus Christi feast.
The mountain sits at an elevation of 6,384 meters and is located approximately 100 km southeast of the major city Cusco. The local area is rich in geology, from uplifted granitic cliffs to glaciers which have eroded large valleys and the cretaceous limestone “forest” nearby.
The Andes are an incredibly complex mountain chain that extends along the western edge of the South American continent. The subduction of the Nazca plate underneath the South American plate initiated mountain building and uplift of the mountain range. This produced significant volcanism and the introduction of rare and varied mineralogy to the Andes Mountains.
The reason we see the rainbow coloration in the stratigraphic layers of the Ausangate mountain is largely due to weathering and mineralogy. Red coloration of sedimentary layers often indicates iron oxide rust as a trace mineral. Similar to how a nail will rust and turn red when oxidized, sediments that are iron rich will change when exposed to oxygen and water. This, in combination with uplift and tectonically driven crustal shortening has tilted the sedimentary layers on their side exposing stripped stratigraphic intervals.
The different coloration is due to different environmental conditions and mineralogy when the sediment was originally deposited and subsequently diagenetically altered. Introduction of goethite or oxidized limonite will introduce a brownish coloration to sandstones. The bright yellow coloration could be due to iron sulphide as trace minerals within the pore cement. In addition, chlorite will often color sediments varying shades of green dependent on diagenetic history and concentration.
As your eye scans the many layers of the Peruvian Painted Mountain you’re seeing millions of years of history and all the complexities that are associated therein. Understanding the environmental and geologic conditions that formed the rock units we see today is one of the key building blocks of geology and allow us to better understand our world long before humans walked this green Earth.