Puente del Inca

Useful Information

photography — Puente del Inca, Argentinia. Public Domain.

Location:	Ruta Internacional n°7, near Puente del Inca, east of Las Cuevas, Mendoza Province. (-32.826733114280180, -69.910629308379070)
Open:	No restrictions. [2022]
Fee:	free. [2022]
Classification:	Natural Bridge
Light:	n/a
Dimension:	L=28 m, W=47 m, A=2,717 m asl.
Guided tours:	self guided
Photography:	allowed
Accessibility:	yes
Bibliography:	Victor A. Ramos (2009): Darwin at Puente del Inca: Observations on the Formation of the Inca's Bridge and Mountain Building, Revista de la Asociación Geológica Argentina 64 (1):170- 179 (2009) researchgate W. Schiller (1907): Geologische Unterschungen bei Puente del Inca (Aconcagua) Vorläufige Mitteilung, Neues Jahrbuch für Mineralogie, Paläontologie und Geologie, Beilageband 24: 716-736. E. Kittl (1941): El Puente del Inca: su formación y conservación Revista Minera 12(3-4): 110-122, Buenos Aires.
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History

1646	first written mention by Alonso de Ovalle.
1820	first description by Schmidtmeyer.
1826	description by John Miers.
1827	samples of the thermal springs obtained by British traveler Charles Brandt and chemical analyses by the physicist and chemist Michael Faraday.
04-APR-1835	visited by Charles Darwin.
1902	Christiano Junior claims that it was an old Inca bridge built with wood and rattan which was later covered by limestone from the springs.
1907	W. Schiller guesses a crust growth from the thermal springs reached the opposite margin of the valley by means of slow lateral precipitation.
1941	E. Kittl studies the bridge and improves Darwin's original hypothesis.
1953	spa destroyed.
1984	Transandine Railway shut down.
2005	ruins closed due to the danger of collapse.

Description

Puente del Inca (The Inca's Bridge) is a natural bridge at the Vacas River, a tributary of the Mendoza River. The bridge is extraordinary because it was actually formed by a hot springs. The hot water deposits huge amounts of minerals with a generally yellowish colour, which form huge lumps, plateaus and even stalactites. The bridge probably formed by the combination of ice and deposited minerals. During colder climate in the last cold age the river bed was filled with ice all year. The ice and the hot water were in a sort of equilibrium of melting and freezing, and while the surface of the ice stayed at a certain level above the river bed, the hot water deposited a crust of rock on top. Snow avalanches and landslides deposited further material which was cemented by the minerals from the hot-water springs. This formed the bridge as a mineral deposit, so it is not of erosional origin as some webpages state.

The most famous visitor of the bridge was probably Charles Darwin, who visited Puente del Inca during his second journey across the High Andes. He already realized the way it formed. He also found shallow water marine fossil mollusks intermingled with volcanic rocks. This led to new theories about mountain uplift, the subsidence of the marine bottom, the episodic lateral growth of the cordillera, and their association with earthquakes and volcanic activity. Although he was not impressed by the bridge, the influence of this location on the development of geology are of great importance. He made some drawings of the bridge with large stalactites. However, the engraving which was published in one edition of his book does not really resemble the original bridge.

5th [4th] From the Rio de las Vacas to the Puente del Inca, half a days journey; here was a little pasture for the mules; & some interesting geology for me, so we bivouaced for the night. When one hears of a Natural bridge, one pictures to oneself some deep & narrow ravine across which a bold mass of rock has fallen, or a great archway excavated. Instead of all this the Incas bridge is a miserable object. The bottom of the valley is nearly even & composed of a mass of Alluvium; on one side are several hot mineral springs, & these have deposited over the pebbles |554| a considerable thickness of hard stratified Tufa; The river running in a narrow channel, scooped out an archway beneath the hard Tufa; soil & stones falling down from the opposite side at last met the over hanging part & formed the bridge. The oblique (D) junction of the stratified (A) rock & a confused mass is very distinct & this latter is different from the general character of the plain (B). — This Inca's bridge is truly a sight not worth seeing. —
Charles Darwin: Beagle Diary (1831-1835)

He already realized the ice and the hot springs as the major reasons for its formation. But his observations on the genesis of the bridge were unpublished, so they were not considered for many years. The Diary of the beagle was first published in 2009. The following passage is the explanation to a small pencil sketch from his field notebook.

Incas bridge irregular hilly plain of valley filled up with pebbles & detritus a fan of ferruginous cellular Tufa covering a part: the river having cut as far as (x). continued to scoop out to the Southward; rubbish (B) fell down from plain I supported circled [page 202a] (m) whilst river, continued forming arch. - the oblique junction is very evident (horizontal & confined) plain generally horizontal gravel this not so; hence rubbish: - My hypothesis of Tufa is that it was deposited after valleys excavated & just before sea retired; matter before that generally deposited - hence Tufa from these Springs extends above ... in the slope, above their level: Springs hot - violent emission of gaz: Concretions, where water drips.
Charles Darwin field notebook, pages 201-202a.

The sulfuric spring is also named Puente del Inca, and was the reason for the construction of a big thermal resort and Spa in the early 20th century. The hotel was destroyed by a landslide or avalanche in 1953, and never rebuilt. There is now a spa further down the river at Cacheuta. The remains of the hotel offered a way to get under the bridge, but the building and the bridge were closed in 2005 due to the danger of collapse.

The Ferrocarril Trasandino (Transandine Railway) once ran along the river towards Chile. Here was the second last station in Argentina before it entered the 3.2 km long Cumbre Tunnel across the border. The guests of the spa arrived with the train. The nearby train station Puente del Inca was abandoned in 1984 and has been turned into a mountaineering museum. The Museo del Andinista was founded by a group of mountain climbers from Rosario province.