Cordillera de la Sal

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Cordillera de la Sal
The Cordillera de la Sal (literally: salt mountains) is a karst landscape formed from red sedimentary rock and white evaporite. Table salt and plaster of paris make them look almost like a snowy landscape in their central areas.

The Cordillera de la Sal (literally: salt mountains) is a karst landscape formed from red sedimentary rock and white evaporite . Table salt and plaster of paris make them look almost like a snowy landscape in their central areas.

Highest peak Cerro el Marmol ( 2659  m )
location ChileChile Chile
San Pedro de Atacama
part of To the
Coordinates 23 ° 3 ′  S , 68 ° 22 ′  W Coordinates: 23 ° 3 ′  S , 68 ° 22 ′  W
rock Red sediments, sandstone, sand, evaporites
Age of the rock Oligocene / Miocene

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Viewed from about 40 km away, the Cordillera de la Sal looks quite inconspicuous. From the base of operations of the ALMA radio telescope at the foot of the Andes-West Cordillera at 2900 m above sea level. M. seen from, the Cordillera de la Sal with its maximum 2660 m above sea level. M. only a narrow strip that rises on the edge of the Salar de Atacama (in the foreground, 2300 m above sea level), in front of the much higher dark mountains of the Andean Prekordillere, whose peaks 3000 to 4300 m above sea level. Reach M.

The Cordillera de la Sal is a mountain range in the Preandine Depression near San Pedro de Atacama in northern Chile. It was created by tectonic activity in the Salar de Atacama, during which layers of continental red sediments and white evaporites were unfolded and lifted. Over the past 4000 years, erosion by the water of the rare rainfall in this extremely hyperarid region has formed a bizarre karst landscape with superficial salt efflorescence and salt caves. Due to sterile salt soils, bone-dry climate and intense sunlight, the mountains are mostly an absolute desert.

geography

(  Map with all coordinates: OSM | wikimap ) The Cordillera de la Sal is a mountain range within the endorheischen , präandinen Salaren- Valley , which lies in northern Chile some 150 km from the coast, nestled between the Cordillera de Domeyko (Andean Precordillera ) in the west and the Andes-Western Cordillera in the east. The mountain range is a narrow, low fold mountain range in relation to its wider surroundings . With a width of 5 to 10 km, it extends in a north-northeast orientation over a length of more than 100 km. It divides the Preanden Basin at this point into two water catchment areas, the Salar del Llano de Paciencia Basin (approx. 2500 m above sea level) in the west and the Salar de Atacama Basin (2300 to 2350 m above sea level). ) in the East. In the north it joins the Andes-Western Cordillera at the San Bartolo rhyolite lavadom and in the south it ends in the depression at 23 ° 31'S , where Llano de la Paciencia and Salar de Atacama come together. The mountain range only towers over the surrounding salars by an average of 200 m. Its highest point is the Cerro el Marmol ( 22 ° 54 '  S , 68 ° 18'  W ) with 2659 m above sea level. d. M. at the western end of the Valle de la Luna , a valley that is open to tourists and runs through the mountains in an east-west direction. f1Georeferencing

The Cordillera de la Sal consists mainly of red sedimentary rock ( siltstone , sandstone , conglomerate ) with some tuff layers and with thick layers of continental evaporites ( gypsum , halite ), more than 300 m thick. In some places the wind has piled up large sand dunes.
In the wetter days of the past, draining water dug some wide gullies into the salt rock. Some of these "rivers" meander alternately above and below ground through the mountains.
Table salt is found in pure form, occurring in large crystals, in the Cordillera de la Sal. In the 20th century, local entrepreneurs mined it in open-cast mining and sold it as table salt.
The former home of the Crisanta salt mine ( 22 ° 56 ′  S , 68 ° 20 ′  W , 2490 m above sea level), built from water-soluble quarry salt stones. This was the most industrialized of the salt mines in the Cordillera de la Sal. In 1947 a local entrepreneur had secured the prospecting right for an area of ​​500 hectares on the west side of the Cordillera de la Sal. With the formation of the Los Flamencos National Reserve in 1990, all mining rights were revoked, salt mining prohibited and the mines expropriated. Many salt quarries had previously closed for economic reasons.
The minefields on the Cordillera de la Sal are a dangerous burden from the time of the military dictatorship . They are only conspicuously marked if it is known where they are. This picture shows a sector ( 22 ° 55 ′  S , 68 ° 20 ′  W ) on the now closed, historic route of Ruta 23 , which crossed the Cordillera de la Sal through the Valle de la Luna to San Pedro de Atacama.

climate

The mountains belong to the extremely hyperarid core of the Atacama Desert , which is defined by the fact that the aridity index can drop to 0.002. This means that up to 500 times more water could evaporate there than is brought in by the scant rainfall . For the mean annual precipitation height values ​​of 6 mm to a maximum of 50 mm were determined and for the annual potential evapotranspiration 1800 to 3200 mm. The mean air temperatures are 13.1 ° C, with a minimum of −1.8 ° C and a maximum of 32.2 ° C. The dryness of the air, aggravated by the altitude, causes large temperature differences between day and night, which can be 20 to 30 ° C. That is why there is hardly any cloud formation and only a thin ozone layer, so that the mountains and their surroundings are exposed to the world's highest solar irradiance . This applies to both total solar radiation and the proportion of UV radiation .

landscape

The mountain range is a karst landscape. The water-soluble salt rock forms a very irregular plateau, intersected by sinkholes and disordered drainage patterns. Rivers, some of which run underground, are interrupted by gypsum towers (hoodoos), which are often aligned along the main structure direction. The karst phenomena developed mainly in the previous wetter climate.

Despite the prevailing hyperarid climate, the landscape is currently still being severely eroded. The erosion rates are 4.8 mm / a on horizontal surfaces, 2.4 mm / a on vertical surfaces and in caves still 1 mm / a.

There are numerous karst caves that have been created over the last 6000 years by water flows after sporadic rainfall. More than 50 of them are known so far (as of 2017), some of which are more than 2 km long and all together 15 km. Many are through caves with an upper, vertical entrance (shaft or collapse), which leads into an underground, horizontal rock salt passage, which gradually widens towards the exit with a slight incline, straight or meandering.

For example the Chulacao Cave. It is located on the east side of the Cordillera de la Sal around 4 km from San Pedro. It is the largest and probably the oldest cave in the area. The canyon-like passage reaches up to 20 m in height and 25 m in width. With a length of 859 m, it has a volume of approx. 20,005 m³. At its exit to the Salar de Atacama is the historic Chulacao copper mine ( 22 ° 55 ′ 29 ″  S , 68 ° 14 ′ 20 ″  W ).

A noticeable landscape element are gypsum towers up to ten meters high, which are sometimes referred to as hoodoos and often jut out of the ground in linear arrangements. They are made up of large crystals that have grown out of the plane along fractures. It is very likely that these structures are geomorphologically active in that they continue to grow slowly through recrystallization processes in the subsurface. Its base probably extends deep into the ground and forms barriers for the groundwater that flows from the higher ridges into the lower parts of the plain. The groundwater is forced to rise along the fractures and evaporation processes lead to the formation and growth of gypsum crystals.

ground

The soil in the mountains is characterized by a high salt content ( electrical conductivity 15.4 S / m, pH 7.6), low moisture content (0.004%) and low content of organic material (0.03%). In comparison, the equally dry and salty soil in the neighboring salt flat of the Salar de Atacama has almost twice as much moisture and only one eleventh of the electrical conductivity. Due to the harsh environmental conditions, most of the mountains are an absolute desert. There are no plants or animals there and only a few specialized microorganisms.

The environment in the Cordillera de la Sal is a dry line for bacterial life on earth. As the only life form so far only a few, rare Actinomycetales have been found in the soil . These are endolithic bacteria that protect themselves from UV radiation by living at least a few millimeters below the surface within the partially translucent salt rock. They protect themselves from drying out with the help of the little water enclosed in or between the salt crystals. Pharmaceutical research is interested in the rare and novel bacterial taxa found in this desert because they produce bioactive substances.

The hyperarid and hypersaline environmental and soil conditions make the Cordillera de la Sal a promising research model and laboratory for soils on Mars. Evaporite deposits containing chloride have already been discovered there, and scientists therefore assume that life could also exist in the hygroscopic salts on Mars and that karst caves could have formed. In order to be able to find caves on Mars and perhaps also on the moon, remote sensing methods are also being tested in the caves of the Cordillera de la Sal.

Emergence

The Salar de Atacama depression has been a drainless basin for around 30 million years . Initially, this was essentially filled by the alluvial cones and evaporites ( gypsum , anhydrite , glauberite and halite ) from the rivers coming from the west and north , and so kilometer-thick layers of salt rock formed .

The original center of the basin was southwest of today's San Pedro de Atacama, between the Valle de la Luna pass and the Domingo Ramos pass ( 23 ° 3 ′  S , 68 ° 21 ′  W ). Finally, there was a small central salt pan in which thick layers of halite were deposited, while the center of the Salar de Atacama depression shifted further south over time. Up until 20 million years ago, volcanic activity in the neighborhood also brought in some thin layers of tuff.

The basin sank a little under the weight of the increasing sediments and tilted slightly. As a result, the unconsolidated sediments began to slide towards the center of the basin under the influence of their own gravity about 12 to 5 million years ago (Upper Miocene) and caused a folding through a horizontal compression . A process that has continued over time and may still continue today.

Salt mining

Halite, whose thickness is several tens of meters and whose immersion layers are different, was also the subject of artisanal mining. Archaeologists have now identified 17 salt mines, or more precisely quarries, from the first half of the 20th century. Maybe that's not all that have existed.

Minefields

The mountains are not far from the border with Bolivia and Argentina. Originally the road from Calama to San Pedro de Atacama crossed the Cordillera de la Sal through the Valle de la Luna to the border. In 1978, minefields were created around the pass road on the west side of the Cordillera de la Sal to allegedly protect against a military invasion from Bolivia . These still make parts of the mountain inaccessible today.

Web links

Commons : Cordillera de la Sal  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e f g Jean Sesiano. "The phenomènes karstiques dans une des régions les plus arides du Globe: le désert d'Atacama, au nord du Chili." Archives des Sciences 50.2 (1997): 87-94. ( online )
  2. ↑ a b c Soviet General Staff Map XF19-XXVIII (1980), 1: 200,000 ( online )
  3. ↑ a b c d e Eberhard Wilkes, Konrad Gorier. "Evolution of the Cordillera del la Sal, Northern Chile." Structure and evolution of the Central Andes in northern Chile, southern Bolivia and northwestern Argentina. Final workshop. 1990. ( PDF )
  4. ↑ a b c d e f g h Eberhard Wilkes, Konrad Gorier. "Sedimentary and structural evolution of the Cordillera de la Sal, II Región, Chile." Congreso Geológico Chileno. Vol. 1. 1988. ( PDF )
  5. ↑ a b c d e f Eberhard Wilkes, Konrad Gorier. "Sedimentary and structural evolution of the Salar de Atacama depression." Tectonics of the Southern Central Andes. Springer, Berlin, Heidelberg, 1994. 171-188. ( online )
  6. ↑ a b c d e f Jo De Waele, Cristina Carbone, Laura Sanna, Marco Vattano, Ermanno Galli, Francesco Sauro, Paolo Forti. "Secondary minerals from salt caves in the Atacama Desert (Chile): a hyperarid and hypersaline environment with potential analogies to the Martian subsurface." International Journal of Speleology, 46.1 (2017): 51-66. Tampa, FL (USA) ISSN 0392-6672, doi : 10.5038 / 1827-806X.46.1.2094
  7. ^ A b Jose Antonio Naranjo, Carlos Felipe Ramirez, Roland Pankoff. "Morphostratigraphic evolution of the northwestern margin of the Salar de Atacama basin (23 S-68 W)." Andean Geology 21.1 (1994): 91-103. ( PDF )
  8. ↑ Laura A. Evenstar, Adrian J. Hartley, Stuart G. Archer, Joyce E. Neilson. "Climatic and halokinetic controls on alluvial – lacustrine sedimentation during compressional deformation, Andean forearc, northern Chile." Basin Research 28.5 (2016): 634-657. doi : 10.1111 / bre.12124 ( PDF )
  9. ^ Arturo Belmonte Pool. "Crustal seismicity, structure and rheology of the upper plate between the precordillera and the igneous arc in northern Chile (22 ° S-24 ° S)." Dissertation FU 2002 ( online )
  10. ↑ Juan Fernando Rubilar, Juan Becerra, Cesar Arriagada. "Structure of the Cordillera de la Sal: A key tectonic feature for the Oligocene-Neogene evolution of the Salar de Atacama basin, Central Andes of Northern Chile." XIV Congreso Geológico Chileno. 2015. ( PDF )
  11. ↑ a b c Flora Vilches, Lorena Sanhueza, Cristina Garrido, Cecilia Sanhueza, Ulises Cárdenas. "La minería de la sal durante el siglo XX in San Pedro de Atacama, Chile (II Región): entre la explotación artesanal y la industrialización." Estudios atacameños 48 (2014): 209-228. ( online )
  12. ↑ a b c Chinyere K. Okoro, Roselyn Brown, Amanda L. Jones, Barbara A. Andrews, Juan A. Asenjo, Michael Goodfellow, Alan T. Bull. "Diversity of culturable actinomycetes in hyper-arid soils of the Atacama Desert, Chile." Antonie Van Leeuwenhoek 95.2 (2009): 121-133. doi : 10.1007 / s10482-008-9295-2 ( PDF )
  13. ↑ J. DiRuggiero, J.Wierzchos, CK Robinson, T. Souterre, J. Ravel, O. Artieda, V. Souza-Egipsy, C. Ascaso. "Microbial colonization of chasmoendolithic habitats in the hyper-arid zone of the Atacama Desert." Biogeosciences 10 (2013): 2439-2450. doi : 10.5194 / bg-10-2439-2013
  14. ↑ a b Jacek Wierzchos, Jocelyne DiRuggiero, Petr Vítek, Octavio Artieda, Virginia Souza-Egipsy, Pavel Škaloud, Michel Tisza, Alfonso F. Davila, Carlos Vílchez, Inés Garbayo, Carmen Ascaso. "Adaptation strategies of endolithic chlorophototrophs to survive the hyperarid and extreme solar radiation environment of the Atacama Desert." Frontiers in microbiology 6 (2015): 934. doi : 10.3389 / fmicb.2015.00934
  15. ↑ a b Jo De Waele, Vicenzo Picotti, Luca Zini, Franco Cucchi, Paolo Forti. "Karst phenomena in the Cordillera de la Sal (Atacama, Chile)." Geoacta (2009): 113-127. ( online )
  16. ↑ a b Jo De Waele, Vicenzo Picotti, Paolo Forti, George Brook, Franco Cucchi, Luca Zini. "Age of caves in the Cordillera de la Sal (Atacama, Chile)." 15th International Congress on Speleology, Kerrville, Texas, USA. National Speleological Society. 2009. ( online )
  17. ↑ J. Judson Wynne, Timothy N. Titus, Guillermo Chong Diaz, Christina Colpitts, W. Lynn Hicks, Denise Hill, Daniel W. Ruby, Cristian Tambley. "Cave Microclimate Data Retrieval and Volumetric Mapping, 2009 Atacama Desert Expedition, Chile, Earth-Mars Cave Detection Project": Explorers Club Flag Report (Flag. # 52) ( PDF )
  18. ↑ Jo De Waele, Paolo Forti. "Salt rims and blisters: peculiar and ephemeral formations in the Atacama Desert (Chile)." Journal of Geomorphology, Supplementary Issues 54.2 (2010): 51-67. doi : 10.1127 / 0372-8854 / 2010 / 0054S2-0004 ( PDF )
  19. ^ J. Judson Wynne, Timothy N. Titus, Guillermo Chong Diaz. "On developing thermal cave detection techniques for Earth, the Moon and Mars." Earth and Planetary Science Letters 272.1 (2008): 240-250. doi : 10.1016 / j.epsl.2008.04.037
  20. ↑ Constantino Mpodozisa, César Arriagada, Matilde Basso, Pierrick Roperch, Peter Cobbold, Martin Reich. "Late Mesozoic to Paleogene stratigraphy of the Salar de Atacama Basin, Antofagasta, Northern Chile: implications for the tectonic evolution of the Central Andes." Tectonophysics 399.1 (2005): 125-154. ( PDF )
  21. ^ A b Robert J. Dingman. "Tertiary salt domes near San Pedro de Atacama, Chile." US GeoL. Surv. ProJ. Pap., 450-D (1962): 92-94. ( PDF )
  22. ^ Ministerio de Defensa Nacional. "Convención sobre la prohibición del empleo, almacenamiento, producción y transparencia de minas antipersonales, y sobre su destrucción." 12 ° Informe de medidas de transparencia. April 30, 2013 ( PDF )