A volcanic eruption that occurred 22 million years ago has provided scientists with a rare glimpse into the early formation of the Andes Mountains. The eruption took place at the Lauca Caldera, located in what is now northern Chile, and covered the surrounding area with ignimbrite—a type of rock formed by fast-moving pyroclastic flows. These flows, composed of volcanic gas, ash, and rock, moved across the landscape like a boiling wave, similar to the event that destroyed the Roman city of Pompeii during the eruption of Mount Vesuvius in 79 AD. A recent study published in the journal Science Advances on September 11 has reconstructed the landscape that existed before this volcanic event. The researchers found that the area was covered by rolling foothills, not the steep, rugged peaks seen in the Andes today. Byron Adams, a geomorphologist from University College London, explained that such eruptions can preserve snapshots of Earth's history, offering clues about how mountains formed before the event. By analyzing the shape of the ignimbrite layer and how rivers shape landscapes, the team inferred the topography that existed beneath the volcanic deposits. The volcanic flow from Lauca Caldera originally had a slope of about 1.5 degrees. Adams and his colleagues used this information to calculate the rate at which the land was rising due to the collision of the oceanic Nazca Plate with the continental crust of South America. Their findings suggest that the uplift of the Earth's crust in this region occurred at a very slow pace—no more than 0.16 miles (0.26 kilometers) per million years. This slow process supports earlier studies that used mineral formation within rocks to determine when they rose through the Earth’s crust. There has been ongoing debate among scientists about the timeline of the Andes' formation. Some argue that the mountains grew steadily over 40 to 50 million years, while others suggest a more recent, rapid uplift in the last 6 to 10 million years. Adams' study supports the idea of a slow and steady growth process. The research methods used could also be applied to other mountain ranges around the world, helping scientists better understand how different landscapes have evolved over time.