The Andes mountains along the western edge of South America form a 4 km high (~ 13,000 ft) and 500 km wide (~ 310 mile) plateau in the countries of Peru, Bolivia, northern Chile and Argentina. Carved into the northeastern edge of the plateau are dramatic, 2-3 km deep canyons (30% to 50% deeper than the Grand Canyon). Previous researchers have argued that the increased river incision forming these deep canyons reflect either a significant increase in the elevation of the plateau over the last 5 million years, or a pronounced change in climate that delivered more rain to the high and dry portions of the Andes, resulting in increased river discharge and erosional power.
In their Science Advances manuscript published November 5th, Jennie Plasterr and co-authors argue, based on data from one of these canyons (the San Gaban), that the canyon was incised when the San Gaban River captured a higher elevation, internally drained river system, resulting in a dramatic increase in the area that drains to the river, and, hence, its discharge and ability to carve through rock. The San Gaban was able erode through a ridge-line and capture the higher elevation river system at approximately 10 million years ago, because tectonic forces that were pushing the ridge-line upward and resisting erosion slowed considerably at this time. By comparing the shape of the rivers and canyons that cut into the eastern edge of the plateau in Peru and Bolivia, Plasterr argues that not just the San Gaban but potentially all of the large canyons were formed due to such river capture as tectonic uplift slowed.
River capture events are not unique to South America. In Pittsburgh and Appalachia, for example, past river capture events play a key role in forming the steep topography that characterizes the region.
Link to the Research Article.