The Cerro Blanco volcanic complex sits at the southern edge of the Andes in Argentina. Researchers analyzed ash deposits across a broad area in northwest Argentina to reconstruct the dynamics and reach of a monumental eruption from centuries past.
Located in the far south of the Andes, the Cerro Blanco Volcanic Complex erupted about 4,200 years ago. This event stands out as the largest eruption in the central volcanic zone of the Andes during the last five millennia.
The sheer volume of erupted rock places this event among the biggest Holocene eruptions, a finding confirmed by a 2019 study led by José Luis Fernández Turiel of the ICTJA-CSIC Jaume Almera Institute of Earth Sciences and carried out by a collaborative team from Spanish and Argentine universities and research institutions.
In the Cerro Blanco area, extensive ash deposits remain visible across a wide swath of the Andes. The existence of the volcano was known, but its origin was not clearly understood until now.
It was possible to confirm that the Cerro Blanco eruption produced the large Holocene ash blankets that covered broad parts of the Puna region and neighboring areas in northwestern Argentina, according to José Luís Fernández Turiel.
Reconstruction with digital simulations
The presence of plant remains in sediments adjacent to the ash layers allowed carbon-14 dating, pinpointing the eruption at 4,200 years ago. Digital simulations traced the transport and fallout of the ash. The eruption was highly explosive, dispersing ash over roughly 500,000 square kilometers, an expanse roughly the size of Spain. Ash traces were found as far as 400 kilometers from Cerro Blanco, near 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 evacuation of magma led to the collapse of the chamber and the formation of a complex caldera.
Researchers also mapped the ash’s spread with micrometric precision, aided by field observations and geological studies. The eruptions formed a very tall explosion column that simulations indicate could have reached heights near 32 kilometers. The total ash volume exceeded 170 cubic kilometers, enabling the calculation of a Volcanic Eruption Index of 7 for Cerro Blanco. This places it among the most powerful events of the last ten millennia, comparable to renowned ancient eruptions and significantly 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 previous assumptions about regional activity patterns.
This finding provides researchers with a valuable temporal framework for studying the mid-Holocene geologic, archeological, and paleoclimatic features across a large portion of South America.
An archaeologist from the Institute of Culture at the University of Buenos Aires notes that these findings offer new information to interpret hunter-gatherer societies in the southwestern regions of 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 archeological records to illuminate how mid-Holocene populations adapted to dramatic volcanic events across this part of the continent. 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 discussed in the broader body of work on Holocene volcanism in this region. This body of 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 referenced here synthesizes geological, archaeological, and paleoclimatic perspectives to offer a coherent view of how one colossal eruption shaped landscapes and societies across the region.
Source: Estudio Geol. Investigations into mid-Holocene volcanism in the Central Volcanic Zone are summarized by researchers from Spanish and Argentine institutions, including the ICTJA-CSIC and collaborators. The findings 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 discussed in ongoing analyses from collaborating center studies and regional colleagues. This synthesis emphasizes how single volcanic events can rewrite regional histories and environmental trajectories across continents.