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!

Lima, Peru’s Historic Centre – A UNESCO World Heritage Site and the Earth-Shattering Events That Helped Shape It

Lima, Peru is fast becoming a preeminent food hotspot with traditional Peruvian foods and various fusion cuisines that I found extremely delicious. And of course it is also internationally known for extraordinarily magnificent museums such as the Museo Larco with its collection of pre-Columbian art.

Lima, the capital city of Peru, has a population of almost 10 million people that is dispersed among its 43 districts. Known as the “City of Kings”, Lima was founded by the Spanish conqueror Francisco Pizarro in January 1535 when Pizarro confiscated land on the south bank of the Rimac River where the Inca curaca (local ruler), Taulichusco, had his palace. Lima then became the most important city and capital of the Spanish holdings in South America until the mid 1700’s. Lima’s supremacy later diminished as northern South America became a part of the Spanish Empire (known as the Viceroyalty of New Granada and established in 1717) and with the creation in 1777 of the Viceroyalty of La Plata, which encompassed the present-day territories of Argentina, Bolivia, Paraguay.

Historic Centre of Lima

The Historic Centre of Lima was declared a UNESCO World Heritage site in 1988. As noted in UNESCO’s  description of this site:

“The authenticity of the Historic Centre of Lima is intact as it largely preserves the original features of its urban foundation design, as a checkerboard, and the expansion area from the XVI to the XIX century, including old pre-Hispanic paths heading North (Chinchaysuyo) and East (Antisuyo).”

The Plaza de Armas in the Historic Centre of Lima. The bronze fountain, erected in 1650, sits in the Plaza's center. The Cathedral of Lima is seen here directly in back of the fountain.

The Plaza de Armas in the Historic Centre of Lima. The bronze fountain, erected in 1650, sits in the Plaza’s center. The Cathedral of Lima is seen here directly in back of the fountain.

The Plaza de Armas is near the center of the Historic District and thought of as the birthplace of the city. There is no original building remaining adjacent to the plaza, but the bronze fountain in the Plaza’s center was erected in 1650. Some of the more significant buildings now surrounding the Plaza include the Cathedral of Lima, the Government Palace, and the Archbishop’s Palace of Lima.

The construction for the first church on the Cathedral of Lima site was completed in 1538. The present cathedral is the result of many renovations and rebuildings and is largely based on the original plans of the Cathedral that was devastated in 1746.

The Government Palace houses the official residence of Peru’s President and executive branch. The palace’s original construction began in 1535 over the residence of Taulichusco, the then Inca curaca. Similar to the Lima Cathedral, the Government Palace has been extensively rebuilt over the years.

The Archbishop’s Palace is sited on land that Pizarro designated for the head priest of Lima’s residence shortly after the city’s foundation in 1535. The present Archbishop’s Palace was built in 1924 and is well known for its ornate Moorish-style balconies.

San Francisco Monastery in Lima's Historic Centre. The Monastery is well-known for its catacombs.

The San Francisco Monastery in Lima’s Historic Centre. The Monastery is well-known for its catacombs.

Two of the other places that I visited – and I think are well worth going to – in the Historic Centre are the San Francisco Monastery and the Plaza San Martin. The San Francisco Monastery (Convento de San Francisco) is one block northeast from the Plaza de Armas. The Monastery was consecrated in 1673 and completed in 1774, although it has been extensively repeatedly rebuilt. Of note are its famous catacombs where a series of underground burial vaults were used until the mid 1800’s.

Plaza San Martin was dedicated on July 27, 1921 to honor the 100th anniversary of Peru’s independence. The statue of Jose San Martin is central to the Plaza.

Plaza San Martin was dedicated on July 27, 1921 to honor the 100th anniversary of Peru’s independence. The statue of Jose de San Martin is central to the Plaza.

The Plaza San Martín is located about 5 blocks southwest of the Plaza de Armas. The Plaza was dedicated on July 27, 1921 to honor the 100th anniversary of Peru’s independence. An equestrian statue of José de San Martín is the Plaza’s central statue.

A video of Lima’s Historic Centre, done by UNESCO/NHK, gives a good overview of this area:

Lima Area Earthquakes  – the Forces Behind the Rebuilding of the City

As noted several times in the text above regarding Lima’s Historic Centre, no wholly original buildings exist today, and those that do stand today have usually been repeatedly rebuilt. The continued destruction to Lima’s architecture is due primarily to several strong earthquakes in the Lima region that have occurred periodically.

The U.S. Geological Survey (Earthquake Hazards Program, Historic Earthquakes) sets up the geological framework for Peruvian earthquake activity as:

“Peru is located on the western edge of the South American crustal plate, one of several map_south_america_plateslarge lithospheric plates that comprise the Earth’s crust and slowly move with respect to one another. The boundary between the South American plate and the Nazca plate to the west is one of the most seismically active areas of the world. The Nazca plate is being overridden and driven beneath the westward-moving South American plate. This collision between two large segments of the lithosphere is the source of most of Peru’s earthquakes. Offshore, where the two plates meet, the shocks occur at shallow depth. To the east, as the Nazca plate is pushed downward, the earthquakes occur at progressively greater depth – to as much as 600 kilometers near the Peru-Brazil border. … Shallow earthquakes are potentially more destructive than deep shocks of the same magnitude because they generate stronger surface waves.”

Although earthquakes are common in Peru, there have been several significant quakes in the Lima region since its founding. Much of the city was destroyed because of earthquakes in 1586, 1687, and 1746 (Philibosian, 2001) that had magnitudes from 8.6 to 8.7. More recent, large magnitude earthquakes (8.1 to 8.2) in the Lima area occurred in 1940, 1966, 1974 (Dorbath and others, 1990) and also caused substantial building structural damage and loss of life.

And it is not just the ground movement generated by earthquakes that have been devastating for Peru:

“Records indicate that since the late sixteenth century, large earthquakes centered off the Peruvian coast have generated several destructive tsunamis (1586, 1604, 1647, 1687, 1746, 1865, 1868, 1914, 1942, 1960, 1966, 1996). Of those listed, five were particularly destructive. These include the 1586, 1604, 1687 and 1746 tsunamis, as well as the 1868 Arica tsunami.” (USC Tsunami Research Center, 2005)

Probably the most extensive tsunami in the Lima area occurred in association with the 1746 Lima–Callao earthquake (with a moment magnitude recently estimated at 9.0 – Jimenez and others, 2013). Not only did this earthquake cause considerable damage and loss of life in Lima, but the ensuing tsunami basically wiped out the nearby port of Callao:

“On the evening of 28 October 1746, Lima was shaken by a violent earthquake. Out of a population of 50,000, only about 1,000 people died. But at about 11 pm, a tsunami devastated the neighbouring port of Callao, destroying the port itself and sweeping miles inland. In contrast to Lima, only a handful of Callao’s 6,000 inhabitants survived. Lima was then the most important city in South America, and the port of Callao exported gold and silver to Spain. The disaster was unprecedented for the Spanish in the region, and posed a critical economic threat to the colonial power.”  (GAR, 2011)

Given the geologic setting of the Lima, Peru area, it’s a reasonable assumption that earthquake activity is and will be a part of life here.