A massive volcanic eruption that buried part of South America nearly 22 million years ago is giving scientists new insight into how the Andes, one of the world’s tallest mountain ranges, formed.
The study, published in the journal Science Advances, found that the eruption sealed an ancient landscape beneath a thick sheet of volcanic rock, preserving a snapshot of the mountains as they looked millions of years ago.
Scientists have long struggled to measure how fast mountains rise over millions of years, often relying on indirect clues such as the cooling history of rocks or pressure trapped in ancient minerals. The new study offers an independent way to check those estimates by reading the shape of a landscape frozen in time by a volcanic eruption.
Cardones eruption buried Chile-Peru border 22 million years ago
The research was led by Byron Adams, along with co-authors Frances Cooper, Clementine Walsh and Katharine Cashman. The team focused on the Cardones eruption, which covered the western edge of the Central Andes, near the border of Chile and Peru, about 21.9 million years ago.
Scientists believe the eruption came from the nearby Lauca Caldera and released enough hot ash and rock to cover more than 1,260 cubic kilometers (302 cubic miles) of land, leaving behind a gentle slope of about 1.5 degrees.
Because that surface is so flat, researchers said it holds clues about the land buried beneath it. Steep, rugged terrain usually forms when land rises quickly, while gentler terrain forms when the rise is slow, and rivers have more time to wear the landscape down.
Using a computer model that simulates how rivers cut into rock over time, researchers tested hundreds of possible ancient landscapes to see which ones the eruption’s deposits could have completely covered.
Volcanic eruption data show how the Andes formed
The results showed that the Andes were rising slowly and steadily, no faster than about 0.26 kilometers per million years (0.16 miles per million years), when the volcanic eruption struck and formed the flat rock layer seen today. That figure closely matches separate estimates based on rock cooling histories and mineral pressure readings, giving researchers added confidence in the new method.
The findings also point to a wider pattern. Large eruptions capable of producing these flat, far-reaching deposits appear to need calm periods of mountain building rather than times of fast uplift, researchers said. That connection suggests volcanic activity and mountain building in the Andes are more closely linked than previously thought.
Researchers said the same method could apply to other buried landscapes worldwide, including similar volcanic deposits in Alaska, Indonesia and Argentina. It offers a new way to study how mountains form where traditional tools, such as rock dating, are limited or unavailable.
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