What is it about?

We focused our geological study on the understanding of the landscape evolution of the Machu Picchu area. This high-elevation region (> 4000 m) shows striking morphological features: Geological faults and rivers are abnormally curved for instance. Moreover, all around Machu Picchu, the visitor can easily notice impressive deep canyons. We sampled small volumes of granitic rocks along the Inca trail. We extracted apatite minerals in these rocks and used them as chronometers to identify the rock exhumation velocity. We noticed that the present-day landscape, exhibiting deep canyons, is the consequence of an incision pulse cutting through the granite (via the Urubamba river at the foot of Machu Picchu). This pulse of erosion started 4 million years ago and was probably triggered by wetter climate conditions, implying more rains. Additionally, we suspect fault activity, which probably uplifted the Machu Picchu region.

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Why is it important?

Numerous archeological studies addressed the role and function of Machu Picchu by investigating its architecture for example, but none of these studies focused on its proximal landscape evolution. The present-day landscape explains why the Incas chose this site to build the citadel. Studying the long-term landscape evolution (at geological timescale) of this region is a key to also understand the Incas choice. It shows how our environment influences human choices.

Perspectives

Writing this article was a great pleasure as it has co-authors with whom I have had long standing collaborations. I hope this geological approach will satisfy your curiosity.

Dr. Benjamin Gilles Gérard
Universite de Nantes

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This page is a summary of: Pliocene river capture and incision of the northern Altiplano: Machu Picchu, Peru, Journal of the Geological Society, October 2020, Geological Society, DOI: 10.1144/jgs2020-100.
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