Machu Picchu, the ancient Incan sanctuary is considered one of humanity’s greatest architectural achievements. Its site is famous for its perfect integration with the remarkable landscape as it is built in a remote Andean setting over a narrow ridge high above a precipitous river canyon. The sanctuary’s extremely remote location has long puzzled scientists. What prompted the Incas to build their masterpiece in such an inaccessible site? Research now suggests that the answer may be related to the geological faults that lie underneath the site.
This Monday, Rualdo Menegat, a geologist at Brazil’s Federal University of Rio Grande do Sul, at the GSA Annual Meeting in Phoenix, showcased the results of a detailed geoarchaeological analysis that submits that the Incas intentionally built Machu Picchu along with some of their cities in deliberate locations where tectonic faults meet.
Menegat says, “Machu Pichu’s location is not a coincidence. It would be impossible to build such a site in the high mountains if the substrate was not fractured.”
Working with a combination of satellite imagery and field measurements, Menegat mapped a condensed web of intersecting fractures and tectonic faults underneath the UNESCO World Heritage Site. His analysis shows that these features vary widely in scale, ranging from tiny fractures visible in individual stones to major, 175-kilometer-long lineaments that truly control the orientation of some of the region’s river valleys.
Menegat discovered that these faults and fractures occur in numerous sets, some of which match with the major fault zones accountable for uplifting the Central Andes Mountains through the past eight million years. As some of these faults are oriented northeast-southwest while others trend northwest-southeast, they jointly create an “X” shape where they seemingly intersect beneath Machu Picchu.
Menegat’s mapping proposes that the sanctuary’s urban sectors and the adjacent agricultural fields along with individual buildings and stairs are all oriented laterally to the trends of these major faults.
Menegat says, “The layout clearly reflects the fracture matrix underlying the site”.
According to him, other ancient Incan cities like Ollantaytambo, Pisac, and Cusco, are also located at the intersection of faults.
He adds, “Each is precisely the expression of the main directions of the site’s geological faults.”
Menegat’s findings indicate that the underground fault-and-fracture network is as vital to Machu Picchu’s construction as its legendary stonework.
Their mortar-free masonry involves stones so perfectly fitted together that it’s impossible to even slide a credit card between them. Menegat says Incas were master stoneworkers who took advantage of the abundant building materials in the fault zone.
He elaborates, “The intense fracturing there predisposed the rocks to breaking along these same planes of weakness, which greatly reduced the energy needed to carve them.”
According to Menegat, in addition to helping shape individual stones, the underlying fault network at Machu Picchu likely offered the Incas other advantages like there was a ready source of water.
He says, “The area’s tectonic faults channeled meltwater and rainwater straight to the site”.
Menegat explains that construction of the sanctuary in such a high perch also provided the benefit of isolating the site from avalanches and landslides, common hazards in this alpine environment.
The faults and fractures below Machu Picchu also facilitated drain the site during the intense rainstorms prevalent in the region.
Menegat says, “About two-thirds of the effort to build the sanctuary involved constructing subsurface drainages. The preexisting fractures aided this process and help account for its remarkable preservation. Machu Picchu clearly shows us that the Incan civilization was an empire of fractured rocks.”