Rockies Mystery Solved by New Mountain-Creation Theory?
Study "challenges this idea that we understand what's going on," expert says.
Normally mountains form close to coastlines, in places where oceanic plates dive—or subduct—under continental plates (get an overview of plate tectonics). But at about 620 miles (1,000 kilometers) inland, the North American Rockies (see map) are unexpectedly far east from the tectonic collision point.
The prevailing hypothesis for the Rockies' birth, called flat-slab subduction, says that the Pacific oceanic plate dove underneath the North American plate at an unusually shallow angle.
But about 70 million years ago, the diving plate mysteriously rose and started to scrape along the continent's underside, generating friction that pushed up the mountains.
The new theory doesn't rely on odd behavior by the lower plate. Instead
