When Tomas Capaldi looks at the jagged silhouette of the Andes stretching across South America, he doesn't see a mountain range slowly inching skyward over millions of years. He sees a heartbeat. The geoscientist at UC San Diego's Scripps Institution of Oceanography has spent years listening to the deep-time rhythms of the southern Andes, and what he found upended a long-standing assumption about how Earth's great mountain belts come to be.
For decades, scientists believed the Andes rose in gradual, steady increments—tectonic patience made manifest in rock and stone. Capaldi's research reveals something different: the mountains build themselves in powerful, intermittent pulses every few million years, then go quiet. The findings, published in the journal Nature Communications, suggest that mountain-building is not the plodding process textbooks described, but rather a series of dramatic episodes separated by long stretches of geological dormancy.
To uncover this pattern, Capaldi and his team tuned into what he calls the mountain belt's "vital signs." By analyzing volcanic histories embedded in the rock record, tracking structural changes in the crust, and studying sediments that accumulated in nearby basins over millions of years, the researchers traced a repeating mechanism at work. As volcanism migrates inland from the coast toward the continent's interior, it progressively weakens the Earth's crust in its wake. This weakening sets off rapid episodes of deformation—essentially, mountain-building spasms.
"We find that when volcanic activity shifts inland, it weakens the Earth's crust and triggers rapid episodes of mountain building," Capaldi said. "This reveals a repeating pattern behind the rise of the Andes and shows how deep-Earth processes can reorganize quickly enough to reshape landscapes, Earth resources and seismic hazards across South America."
The implications extend beyond geology's abstract fascination with how continents acquire their wrinkles. Understanding this pulse-and-pause rhythm could help scientists anticipate future episodes of mountain growth—and the earthquake hazards that often accompany them. The same volcanic shifts that drive the Andes upward also redistribute stress along fault lines, potentially offering clues about where seismic risk concentrates next.
For the millions of people living in the shadow of these peaks, the discovery reframes an ancient landscape as something dynamic and knowable, governed by patterns scientists can now read like a rhythm waiting to be predicted.