Machu Picchu – The Geological Landscape

Machu Picchu is located in the central Peruvian Andes at an elevation of about 8,000 feet. Huayna Picchu, the closest peak to the ruins, is a favorite hiking area for many visitors amongst whom machu picchu tours are also popular for their spectacular views of this wondrous location.

Much has been written about Machu Picchu since its rediscovery in 1911 by Hiram Bingham and his expedition crew. And although I was truly amazed at the ruins of Machu Picchu when I hiked around it a few months ago, I was mesmerized by the area geology as soon as I got off the train at Aguas Calientes – the town at the base of Machu Picchu. Consequently, it’s the geology of Machu Picchu that I’ll talk about in this blog rather than the ruins. But – for those who would still like to read more background information on Machu Picchu, the Library of Congress has a good online bibliography site for a starting point- Machu Picchu: A Brief Bibliography.

The geographic setting of Machu Picchu –

Map location of Machu Picchu (from Machu Picchu - the lost city).

Map location of Machu Picchu (from Machu Picchu – the lost city).

Machu Picchu lies in the south-central Cordillera of the Peruvian Andes, known as the Cordillera de Vilcambamba. Cusco, the nearest major city, lies about 50 miles southeast of Machu Picchu. Most sojourners like myself access Machu Picchu via the Sacred Valley either by train or by walking the Inca Trail, and stay in Aguas Calientes during their time exploring Machu Picchu.

The geologic setting of Machu Picchu –

Remnant exfoliation sheets on Piticusi Mountain which sits east of Machu Picchu, by Aguas Calientes.

Remnant exfoliation sheets are developed in the granitoid rocks of Piticusi Mountain. Piticusi lies about 0.75 miles east of Machu Picchu and about 0.6 miles southwest of Aguas Calientes.

As soon as I got off the train at Aguas Calientes, I could see that it was a granitic dominated geology. Large remnant exfoliation sheets, typical features of granitic landscapes, cling to the mountainsides in every direction that I looked. Canitu and others (2009, p.250) describe the geology of the the Machu Picchu site as:

“The bedrock of the Inca citadel of Machu Picchu is
mainly composed by granite and subordinately granodiorite.
This is mainly located in the lower part of
the slopes (magmatic layering at the top). Locally,
dikes of serpentine and peridotite are outcropping in
two main levels; the former is located along the Inca
trail, near Cerro Machu Picchu (vertically dipping),
the latter is located along the path toward ‘‘Templo de
la Luna’’ in Huayna Picchu relief.”

Bedrock geology and mass movement areas of Machu Picchu (from Canitu and others, 2009).

Bedrock geology, mass movement areas, and anthropic fill/andenes (agricultural terraces) of Machu Picchu (from Canitu and others, 2009).

The granitoid pluton of Machu Picchu is part of the larger “Quillabamba granite”, which is a magmatic complex now exposed in the eastern Cordillera of central Peru. The Machu Picchu pluton, along with numerous other areal plutons of this magmatic complex, were intruded into an axial zone of a Permo-early Jurassic rift system. Isotopic age data that more tightly constrain this magmatic activity include a (U–Pb) age of 257 +3 My for the Quillabamba granite and a biotite Rb-Sr age of 246 + 10 My for the Machu Picchu pluton (from Lancelot and others, 1978: U/Pb radiochronology of two granitic plutons from the eastern Cordillera (Peru) — Extent of Permian magmatic activity and consequences. Int. Journal of Earth Sciences, 67(1), 236–243). The current exposure of the Machu Picchu pluton at such a high elevation is due to a tectonic inversion of the rift system’s axial zone. The inversion is a result of Andean convergent deformation that occurred largely during the Eocene (Sempere and others (2002) cited in: Mazzoli and others, 2009).

The Macchu Picchu citadel ruins sits within a graben (base image from Google Earth, extracted 6/13/2016).

The Machu Picchu citadel ruins sit within a graben (base image from Google Earth, extracted 6/13/2016).

The site-specific geologic structural setting of Machu Picchu is that the citadel ruins lie within a northeast-trending graben. The graben is delineated by two normal faults with the upthrown side on the northwest including Huayna Picchu and the upthrown side on the southeast being the block that contains Machu Picchu Cerro. As an aside, there are great 1-3 hour hikes that can be done, both to Huayna Picchu and to Machu Picchu Cerro. I did the hike to

The hike up Huayna Picchu is well worth the effort - especially if it's done with a group from the University of Montana.

The hike up Huayna Picchu is well worth the effort – especially if it’s done with a group of people from the University of Montana.

Huayna Picchu with a great group of people, so it was a fun hike made even better by spectacular views from the top of Huayna Picchu.

Building stone of Machu Picchu –

Machu Picchu stone-work construction also incorporated in-place granitoid rock.

Lastly, because the ashlar method of stone block construction (a method where stone blocks are dry fit together so well that it is impossible to slide a piece of paper between the blocks) used in Inca architecture is so fascinating, I’ll include a few words about the stone used in this method at Machu Picchu.

The Temple of Three Windows well illustrates the ashlar building technique used by Inca builders - precisely cut stone blocks (in this case granitoid blocks) that fit so well with adjoining blocks that no mortar is needed.

The Temple of Three Windows well illustrates the ashlar building technique used by Inca builders – precisely cut stone blocks (in this case granitoid blocks) that fit so well with adjoining blocks that no mortar is needed.

The building stone of the Machu Picchu citadel ruins was quarried from the area granitoid rocks. Canuti and others (2009, p. 256) in their study of Machu Picchu slope instability note that:

“As historical consideration, the data collected
suggest the possibility that the site of Machu Picchu
could have been selected by Incas also because of
the availability of two large block deposits, useful
for constructions: one on the so called ‘‘cantera’’
and the second in the paleo-landslide recently
discovered.”

The on-site rock quarry used during the building of Machu Picchu lies near the Sacred Plaza. It is probably often overlooked by visitors because it looks more like just a rocky, chaotic space rather than a worked quarry.

The “cantera” mentioned above is the quarry that was used during the original construction of Machu Picchu. It is located between the Sacred Plaza and the Temple of the Sun at Machu Picchu. It looks like just a chaotic pile of rocks, so is probably not a point of interest for most visitors. The paleo-landslide also mentioned above as a potential source for granitic building material is an area located on the northeast flank of the Machu Picchu citadel ruins. Canuti and others (2009) suggest that it is probably some tens of meters thick and luckily their deformation monitoring did not detect mass movement.

And so ends my 5-part blog series on my adventures in Peru. All I can say is – go there if you get a chance. It is an amazing place!

Peru’s Sacred Valley- Andean Culture With Some Geologic Context

The town of Urubamba is nestled in the Sacred Valley, about 33 miles northwest of Cusco.

The town of Urubamba is nestled in the Sacred Valley, about 33 miles northwest of Cusco.

Most people traverse Peru’s Sacred Valley quickly on their way from Cusco to Machu Picchu. But this stretch of countryside is an area well worth staying around in for awhile, both for getting to know Andean culture and understanding some of its history.

Farming methods in the Sacred Valley are still non-mechanized.

Farming methods in the Sacred Valley are still non-mechanized. Eight varieties of corn are grown in the Sacred Valley, several of which are shown above, on the drying tarps.

The Sacred Valley is considered the heartland of the Inca Empire (1438 to 1533 CE), linking Cusco, the once capital of the Inca Empire, to the world renowned ruins of Machu Picchu. The rich history of this area is evidenced by numerous archaeological sites and a multitude of agricultural terraces that date back to the Inca era. But the region is also a place where contemporary culture mixes with tradition. Quechua-speaking people still farm using non-mechanized techniques and Quecha is often overheard at the numerous markets in the valley’s villages. Yet it is not unusual to see a market vendor using a cell phone or hear someone talking about cable TV.

Hats are a good seller at the Pisac market.

Hats are a good seller at the Pisac market.

Sacred Valley Markets and the Chinchero Weaving Co-op

– Pisac

Village markets in the Sacred Valley are really a treat. One of the largest markets is in downtown Pisac. It is a daily market, with the busier days typically being Tuesdays, Thursdays, and Sundays. The market vendors sell all kinds of items ranging from handmade goods to traditional Peruvian foods.

My guides, Teddy and Ayul, and even I couldn’t pass up buying a hat at the Pisac market!

Textile colors at the Pisac market are amazing.

Textile colors at the Pisac market are amazing.

Chinchero Market and Textile Center

The Chinchero market, with a vendor selling produce and flowers.

The Chinchero market, with a vendor selling produce and flowers.

The market at Chinchero is smaller that the Pisac market, but it is still worth a visit. Although it is typically a daily market, the busiest day is Sunday. But by far the most interesting place to visit in Chinchero is the Textile Center where traditional weaving demonstrations are on-going throughout the day. The weavers use alpaca and sheep wool in their textiles. The demonstrations include much of the textile-making process from wool dyeing to the actual weaving.

Several natural ingredients are used for dyeing wools at the Chincheros weaving co-op.

Several local, natural ingredients are used for dyeing wools at the Chincheros weaving co-op.

The preservation of traditional weaving using alpaca and sheep wool is the focus of the Chinchero weaving co-op.

The preservation of traditional weaving using alpaca and sheep wool is the focus of the Chinchero weaving co-op.

Ruins and Their Geologic Context

The archaeological sites in the Sacred Valley are so numerous (and many are so well known) that I’ll just highlight a few that have some interesting geologic context.

The Maras salt pans have been used for salt production since at least the Inca era.

The Maras salt pans have been used for salt production since at least the Inca era.

— Maras Salt Pans

The Maras salt pans are located less than a mile west of the town of Maras (Maras itself is about 25 miles north of Cusco). The salt pans have been used for salt production since at least Inca times. Maturrano and others (2006) note:

“Maras salterns are located over the Maras Formation in the Cusco Department (13°18′10″S, 72°09′21″W) in southern Peru at an altitude of 3,380 m in the Andes, and they are 1,000 km from the coast. These salterns have been used for salt production since the time of the Incas. Salt is produced mostly during the dry season from May to November. The salterns consist of more than 3,000 small shallow ponds which are not interconnected, so there is no spatial salinity gradient as there is in multipond marine solar salterns. Each pond is filled with hypersaline water from a spring feeding the saltern and empties after salt precipitation, so the ponds act directly as crystallizers. …The origin could be related to the presence in the Maras Formation of underground halite deposits dating to 110 million years ago.”

maras-salt-pack

The salt pans are available to anyone from the community to use for salt production. Once salt is collected, it is physically packed up-slope several hundred feet where it then is distributed to market.

 — Moray

Moray is comprised of concentric agricultural terraces that are built in a carbonate sink hole (doline).

Moray is comprised of concentric agricultural terraces that are built in a carbonate sink hole (doline).

The concentric terraces at the Moray archaeological site are of Inca construction. The terraces are thought to have been built as an agricultural experiment site with each level corresponding to a different microclimate. The hottest microclimate occurs in the deepest part of the terrace construction and temperatures on the terraces decrease upwards. Interestingly, the agricultural terraces are built in a sink hole  (doline) that developed in the area’s carbonate rocks.  Satukunas and others (2002)  say:

“…where the rings of Inca and pre-Inca terraces (the Incas agricultural experiment) are constructed in a karstic doline of some 150 m depth. Active landslide destroyed rings of the 7th-8th terraces and these are currently under reconstruction. The site demonstrates excellent Inca knowledge of management of dolines. ” 

— Ollantaytambo

Terraces and stairways that climb the ruins of Ollantaytambo.

Terraces and stairways that climb the ruins of Ollantaytambo.

Ollantaytambo (located about 37 miles northwest of Cusco) is both an archaeological ruins site and a town. The area was a royal estate of Inca Pachacuti and is also a ceremonial site where Incas resisted Spanish conquest. Of interest to me is that Ollantaytambo contains stone from multiple quarries (Protzen, 1985; Hunt, 1990; Tipcevich, N and Vaughn, K.J., eds., 2012, Mining and Quarrying in the Ancient Andes). It appears that the various successions of builders had their own stone preference ranging from biotite andesite, to granitoid rocks, to the youngest construction phase by Inca Pachacuti of arkose from the nearby Ollantaytambo Formation.

In summary, the Sacred Valley is an area not to be skipped through quickly on the way to Machu Picchu!