A massive volcanic sheet deposited by the Lauca Caldera eruption in northern Chile 21.9 million years ago has provided geologists with a rare geological ceiling. Researchers studying the flat-topped ignimbrite deposit—which spans over 300 cubic miles—have used computer models to infer the hidden, flat landscape beneath, revealing that the Andes rose at a remarkably slow rate of about an inch every 100 years.
Unearthing a Prehistoric Pompeii Scale Event in the Andes
When Vesuvius erupted in 79 C.E., it entombed a Roman city in ash and forever froze a moment of human history. But Earth’s deep geological past holds cataclysms that dwarf historic volcanic events by orders of magnitude. Roughly 21.9 million years ago, a titanic eruption shook what is now the Arica y Parinacota Region in northern Chile. This event laid waste to an ancient landscape roughly six times the size of Santiago, leaving behind an immense blanket of igneous rock known as ignimbrite from the Lauca Caldera.
Here is why that matters for modern earth sciences: rather than just serving as a monument to prehistoric destruction, this colossal volcanic sheet acts as a time capsule. According to findings published in Science Advances, the top of this massive volcanic deposit is remarkably flat. That flatness provides researchers with an upper limit—a physical ceiling—on how rapidly the underlying rock in that sector of the Andes could have been pushed upward prior to the explosion.
“Pompeii shows how volcanic eruptions can freeze a moment in human history. This study shows that much larger eruptions can also freeze moments in Earth history, burying whole landscapes beneath volcanic deposits and preserving clues to how mountains were being built before the eruption,” explained Byron Adams, a tectonic geomorphologist at University College London, in a public statement.
Simulating the Hidden Terrain Beneath the Ignimbrite
Directly observing the topography buried beneath hundreds of cubic miles of dense volcanic rock is practically impossible through conventional drilling. To bypass this physical barrier, the research team turned to sophisticated computer modeling. They simulated hundreds of potential ancient landscapes using established algorithms that demonstrate how surface water and rivers carve and shape mountain ranges over deep time.
“We cannot dig down to see the buried landscape, but we can use the shape of the volcanic blanket and what we know about how rivers shape mountains to infer what is hidden beneath it,” Adams noted.
The models revealed that a low-relief landscape—resembling gentle mountain foothills rather than jagged alpine peaks—lay concealed beneath the Cardones ignimbrite deposits, which are today incised by the Lluta River. If the ancient terrain had been steeply sloped, it simply could not have fit neatly underneath the flat-topped volcanic blanket. This geometric constraint allowed the team to calculate past uplift rates with striking precision.
| Geological Parameter | Data Point | Context |
|---|---|---|
| Eruption Age | 21.9 Million Years Ago | Miocene epoch volcanism in northern Chile |
| Deposit Volume | Over 300 Cubic Miles | Igneous rock layer from the Lauca Caldera |
| Estimated Uplift Rate | ~0.10 miles per million years | Equates to roughly one inch every 100 years |
| Comparison Event | Mount Vesuvius (79 C.E.) | Lauca event covered an area ~6x Santiago’s size |
Redefining the Pace of Continental Mountain Building
For decades, geologists have debated the temporal dynamics of orogeny, the process that forms mountain belts. Traditional methodologies often rely on cooling histories, tracking specific minerals within rocks as they record thermal shifts during their journey upward through Earth’s crust. While powerful, those thermal tracking techniques can carry chronological blind spots.
By studying entire landscapes preserved beneath catastrophic volcanic sheets, geologists gain a macro-scale view spanning vastly broader temporal windows. The data gathered from the Lauca Caldera deposits point toward a slow and steady evolutionary path for this segment of the Andes. The calculated uplift rate—roughly 0.10 miles per million years, or an inch per century—demonstrates that this part of the mountain range rose much more gradually than active, fast-rising belts like certain sectors of the Himalayas.
As international teams continue to analyze these ancient ignimbrite formations, the frozen landscapes of northern Chile offer a sobering reminder. The very forces that devastate can simultaneously preserve the structural secrets of our changing planet for tens of millions of years.
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