The Rocky Mountains are not where they should be
Usually, mountains form along coastlines where tectonic plates collide. Yet, the Rockies sit unexpectedly far inland. For decades, scientists relied on a single-collision theory to explain this anomaly, but new evidence suggests a much more complex, two-stage story of underground suction and ancient obstacles.
The Rocky Mountains, roughly 80 million years old, present a geological puzzle. Typically, mountain ranges emerge near coastlines where oceanic plates subduct beneath continental plates. However, the Rockies are positioned about 620 miles (1,000 kilometers) inland from the primary tectonic collision point. While the long-accepted 'flat-slab subduction' hypothesis suggested a shallow-angled Pacific plate scraped the continent's underside roughly 70 million years ago, recent research is challenging this simplified view.
Geologists from California State University, Northridge, led by Joshua Schwartz and Elena Miranda, argue that the mountains resulted from a two-stage event rather than a single collision. Their findings, published in Nature Communications, suggest two separate collisions occurred over a 50-million-year span, beginning 90 million years ago and concluding around 40 million years ago. This shifts the paradigm from a single coastal impact to a more protracted period of tectonic activity.
A new theory published in Geosphere offers a mechanical explanation for this inland bulge. Lead researcher Craig Jones of the University of Colorado at Boulder proposes that a massive, ancient piece of the lithosphere—potentially up as thick as 180 miles (300 kilometers)—lay beneath what is now Wyoming. As the oceanic plate attempted to dive under this formidable obstacle, it created a 'suction' effect. This tension pulled the continental plate downward and forced mantle rocks to flow into the resulting depression, triggering the deep underground faults that thrust the Rockies upward. While the theory provides a compelling mechanism, scientists note there is currently no solid evidence that such an unusual landmass exists under Wyoming.
Source: The Earth Keeps Making Mountains in Colorado and Scientists Don’t Know Why
