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The Cerro Blanco Volcanic Complex, located at the southern tip of the Andean highlands, erupted about 4,200 years ago. It was not just any eruptive episode, it was the largest eruption in the last 5,000 years in the Central Volcanic Zone of the Andes.
The volume of rock ejected also places it among one of the largest eruptions to have occurred during the Holocene (the last 11,700 years). This is established by a new study carried out by a Spanish and Argentine research team recently published in the journal Geological Studies.
Research personnel from the University of Las Palmas de Gran Canaria and the Institute of Natural Resources have also participated in the work, whose first author is José Luis Fernández Turiel, from the Jaume Almera Institute of Earth Sciences of the CSIC (ICTJA-CSIC). and Agrobiology of Salamanca from the CSIC in Spain, as well as, on the Argentine side, from the National University of Mar del Plata, the National University of Tucumán and the University of Buenos Aires.
The study authors have been able to determine that the Cerro Blanco Volcanic Complex, located in the Argentine province of Catamarca, was the source of extensive volcanic ash deposits, still recognizable in a wide area of the Andean highlands, whose existence until now was known but not its origin.
Researchers studied 62 outcrops in the area and collected more than 230 ash samples during different field campaigns. In order to determine their origin, the samples were analyzed and characterized using different petrological and geochemical techniques.
“Thanks to the work carried out, we have been able to confirm that the eruption that occurred in Cerro Blanco was the one that generated those large deposits of Holocene ash that cover a large area of the Puna and neighboring areas of northwestern Argentina ”, explains José Luís Fernández Turiel.
Reconstruction with digital simulations
In addition, by the plant remains present in the sediments adjacent to the ash layers studied, it was possible to determine using carbon 14 that the eruption took place 4,200 years ago.
Using digital simulations, the authors of the work were also able to reconstruct how was the transport and the fall of the ash.
The Cerro Blanco eruption it was explosive in nature and its virulence was such that the ashes were scattered over an area of about 500,000 km2. In fact, ash from this eruption has been found 400 kilometers away from the volcano, near the town of Santiago del Estero.
Likewise, the pyroclastic flows that occurred filled the adjacent river valleys with thick deposits of ignimbrites, reaching a distance of about 35 kilometers from Cerro Blanco.
The emptying of the magmatic chamber caused by this eruption caused the subsequent collapse of the volcanic building forming a complex volcanic caldera.
“The geodynamic context of the area determines that they are very explosive eruptions. They are eruptions of rhyolitic magma, with a lot of silica and a very high gas content ”, explains Francisco José Pérez Torrado, from the Institute for Environmental Studies and Natural Resources of the University of Las Palmas de Gran Canaria (IUNAT-GEOVOL).
According to Pérez Torrado, “the eruption was not annular, following the edge of the caldera, but rather concentrated at a point on this edge, it was explosive in nature and created a very high eruptive column, almost 32 kilometers high according to our simulations ”.
The volume of ash deposited by this eruption was over 170 km3, which allows the study authors to estimate that the Cerro Blanco eruption had a Volcanic Explosivity Index (VEI) of 7.
A VEI of these characteristics ranks the Cerro Blanco eruption among the largest volcanic events recorded in the last 10,000 years: it is similar to the one that occurred on the island of Santorini which the end of the Minoan civilization and with a volume of magma that doubles to the eruption of the Tambora volcano of 1815, an event attributed to a cooling of global temperatures.
Differences in the behavior of eruptions in the north and south
The present study has its origin in a project carried out previously to determine if the presence of large amounts of arsenic of geological origin in the water of the Chaco-Pampeana Plain was related to the ash deposits of the central and southern volcanic zones of the Andes.
It was during this work that the team of researchers began to characterize the ashes.
"What we were able to verify then is that in the northern part practically all the ash in the deposits we analyzed came from a single source, unlike in the southern area, which came from different volcanoes”, Recalls Alejandro Rodríguez González, a researcher at the IUNAT-GEOVOL.
Fernández-Turiel adds: “The work changes the model of active volcanism in the Andean region. Until now, it was thought that in the Central Volcanic Zone everything worked exactly the same as in the southern zone: many volcanoes with many eruptions over time. What we have seen here is that there are few eruptions, but with a large volume of magma and very high explosiveness ”.
This finding offers researchers an excellent level of temporal guidance for the study of many geological, archaeological and paleoclimatic features, among others, occurred around the middle Holocene in a wide geographic area of South America.
According to Norma Ratto, an archaeologist at the Institute of Cultures of the University of Buenos Aires, “determining the scope and occurrence of this great eruption provides new information to interpret different aspects of the hunter-gatherer societies that inhabited the southern sector of northwestern Argentina throughout the Holocene, such as, for example, the differential occupation of spaces, changes in the mobility of groups due to the modification and alteration of the circulation routes that allowed the connection between different ecological floors, changes in the ecosystems and the health of pre-Hispanic populations, among others ”.
Fernandez-Turiel, JL, Perez-Torrado, FJ, Rodriguez-Gonzalez, A., Saavedra, JC, Carracedo, JC, Rejas, M., Lobo, A., Osterrieth, M., Carrizo, JI, Esteban, G. , Gallardo, J., Ratto, N. (2019) «The large eruption 4.2 ks cal BP in Cerro Blanco, Central Volcanic Zone Andes: Insights to the Holocene eruptive deposits in the southern Puna and adjacents regions«. Geological Studies, 75 (1): e088 https://doi.org/10.3989/egeol.43438.515