An explosive volcanic eruption in northern Chile buried a vast Andean landscape roughly 22 million years ago under a thick, sweeping blanket of ash, rock fragments, and gas. According to researchers led by Byron Adams of University College London, this Pompeii-scale event preserved a remarkably flat ancient terrain, revealing that the Andes mountains grew slowly and steadily.
Unearthing a 22-Million-Year-Old Andean Time Capsule
Mountains often feel eternal, yet they are locked in a relentless planetary tug-of-war. Tectonic forces shove rock upward from deep below, while rainfall and rushing rivers wear those peaks down from above. Quantifying the speed of that tectonic push tens of millions of years ago remains notoriously difficult. Most standard geological methods only capture certain moments in deep time.
That changed in what is now northern Chile. Nearly 22 million years ago, a catastrophic explosion tore through the region, leaving behind the massive Lauca Caldera. Geologists identify the resulting product as the Cardones ignimbrite, the largest of several deposits laid down during a burst of regional volcanism. Similar fiery layers now sit quietly beneath younger towering volcanoes to the east, including Parinacota and Pomerape.
Byron Adams compared the cataclysm to the historic Roman disaster. As Adams explained, this landscape was buried by a giant volcanic eruption—a little like Pompeii, but on a vastly larger scale. Instead of blanketing a single town, superheated flows of ash, rock fragments, and gas swept across an entire landscape, entombing the terrain beneath thousands of feet of debris.
Reading the Volcanic Filter and Ancient Slopes
The sheer scale of the Cardones deposit staggers the imagination. The resulting rock flows accumulate to more than 300 cubic miles, spanning roughly 1,260 cubic kilometers. In certain valleys, the volcanic blanket reaches a thickness of roughly 3,300 feet, or about one kilometer.
Here is why that physical structure matters for modern science. As any volcanic flow travels away from its explosive source, it naturally thins out. Furthermore, the volcanic source must sit at a higher elevation than the ground the flows traverse. Consequently, the buried landscape could not possess a steeper grade than the upper surface of the deposit itself. If the ancient hills had been too steep, their highest peaks would have stuck out above the volcanic blanket.
Adams described the deposit to Earth.com as a natural filter, noting that it preferentially preserves landscapes that were already relatively subdued before the eruption occurred.
Decodign Mountain Growth Through Computer Modeling
A terrain’s steepness depends primarily on the velocity of tectonic uplift and how efficiently rivers carve through bedrock. Rapidly rising rock that resists erosion creates steep country, whereas soft or slow-rising terrain ends up as gentle low hills.
To untangle these variables, Adams collaborated with Frances Cooper, Clementine Walsh, and Katharine Cashman across University College London, the University of Bristol, and the University of Oregon. The research team deployed a specialized computer model simulating river networks cutting into a terrestrial block roughly 14 miles on a side. They ran the simulation 560 times, testing diverse combinations of uplift speed and bedrock erosion resistance.
In each run, simulated rivers carved the land until the topography stopped changing. Only the gentlest simulated landscapes—those tilted no more steeply than the Cardones surface—matched the geological reality found in Chile. By setting erosion resistance to values measured in active bedrock rivers elsewhere, the team calculated that the ancient rock rose no faster than about an inch, or 2.6 centimeters, a century.
| Region / Deposit | Estimated Age | Uplift / Erosion Rate | Geological Significance |
|---|---|---|---|
| Cardones Ignimbrite (Chile) | ~22 Million Years | ~1 inch (2.6 cm) per century | Preserved gentle ancient terrain, proving slow and steady Andean uplift. |
| Taiwan Mountain Belt | Modern Active | 16 to 24 inches (40 to 60 cm) per century | Illustrates high-speed tectonic compression and aggressive surface erosion. |
How Slow Uplift Shapes Global Geological Understanding
An inch a century sounds remarkably slow on a human timescale, but cumulative deep-time arithmetic changes entire continents. To put that pace into perspective, rock in Taiwan rises and erodes at roughly 16 to 24 inches every hundred years.
Mountains do not simply rise like an elevator, Adams noted. As tectonic forces push rock upward, surface erosion simultaneously strips material away. When erosion keeps pace with rock uplift, the visible surface of a mountain range may not climb in elevation very much at all.
For international researchers tracking the mechanics of continental crust formation, these findings offer a vital baseline.
What hidden landscapes lie buried beneath your feet in other volatile tectonic zones across the globe?
