The Cerro Blanco volcanic complex marks the southern edge of the Andes in Argentina, where researchers studied ash deposits across a wide region to reconstruct the scale and reach of a colossal eruption from ancient times.
Situated in the far south of the range, Cerro Blanco erupted about 4,200 years ago. This event stands out as the largest eruption in the central Andean volcanic zone during the last five thousand years.
The sheer volume of erupted material places this event among the most significant Holocene eruptions. A 2019 study, led by José Luis Fernández Turiel of the ICTJA-CSIC Jaume Almera Institute of Earth Sciences and conducted by a team from Spanish and Argentine universities and research centers, confirmed this remarkable magnitude.
In the Cerro Blanco region, extensive ash blankets remain visible across a broad swath of the Andes. While the volcano was known, its origin and full impact were not clearly understood until these investigations clarified its true scale.
The eruption produced large Holocene ash blankets that spread across broad areas of the Puna and neighboring zones in northwestern Argentina, aligning with the detailed findings of the research team.
Reconstruction with digital simulations
Plant remains discovered in sediments adjacent to ash layers enabled carbon-14 dating, pinpointing the eruption at 4,200 years ago. Digital simulations traced how the ash moved and settled. The eruption was highly explosive, dispersing ash over roughly 500,000 square kilometers, an expanse comparable to the size of Spain. Ash traces reached as far as 400 kilometers from Cerro Blanco, toward the vicinity of the town of Santiago del Estero.
Pyroclastic flows filled nearby river valleys with thick ignimbrite deposits and extended up to about 35 kilometers from the volcanic center. The rapid release of magma caused the chamber to collapse and the formation of a complex caldera.
Researchers mapped the ash spread with micrometric precision, supported by field observations and geological studies. The eruptions formed a towering explosion column that simulations indicate could have reached heights near 32 kilometers. The total ash volume exceeded 170 cubic kilometers, yielding a Volcanic Eruption Index of 7 for Cerro Blanco. This places the event among the most powerful in the last ten thousand years, comparable to famous ancient eruptions and far larger than mid-20th century events.
Differences in the behavior of northern and southern eruptions
The discovery reshapes the understanding of Andean volcanism. Rather than a uniform pattern across the Central Volcanic Zone, Cerro Blanco shows that some eruptions produce massive magma volumes and extreme explosivity in relatively isolated episodes, challenging earlier assumptions about regional activity.
This finding provides researchers with a valuable temporal framework for studying mid-Holocene geological, archaeological, and paleoclimatic features across a large portion of South America.
An archaeologist from the University of Buenos Aires notes that these findings offer new information to interpret hunter-gatherer societies in southwestern Argentina during the Holocene. Changes in mobility, shifts in routes, and ecosystem dynamics are among the aspects now better understood thanks to the Cerro Blanco record.
Further studies continue to integrate geological data with paleoenvironmental and archaeological records to illuminate how mid-Holocene populations adapted to dramatic volcanic events across this region. This integrated approach helps explain how ecological and human systems interconnected during that period.
For readers seeking a deeper look, the initial study and related observations are explored within the broader body of work on Holocene volcanism in this region. This research highlights the value of combining ash stratigraphy, radiometric dating, and digital modeling to uncover the history of large-scale volcanic events in the Andes.
Notes and references
The Cerro Blanco eruption is part of a larger conversation on mid-Holocene environmental change in South America. The work described here blends geological, archaeological, and paleoclimatic perspectives to offer a clear view of how one major eruption shaped landscapes and societies across the region.
The findings come from collaborative efforts across Spanish and Argentine institutions, including the ICTJA-CSIC, and draw on ash stratigraphy, radiocarbon dating, and numerical simulations to establish a robust chronology and extent of the eruption. The broader implications for regional archaeology and paleoecology are part of ongoing analyses from collaborating center studies and regional colleagues, illustrating how single volcanic events can influence regional histories and environmental trajectories across continents.