Chapter 27, Problem 2TE

To determine

The driving force for mountain building in the Andes

Answer to Problem 2TE

The subduction is the driving force for mountain building in the Andes

Explanation of Solution

When an oceanic plate collides with a continental plate, the denser oceanic plate will subduct beneath the less dense continental plate. With this oceanic-oceanic convergence, magma is generated. But rising through the thicker continental crust takes longer and this changes the composition of the magma. It becomes more enriched in silica. As the magma begins to rise, the crest melts and gets mixed with the magma.

The Andes Mountains of western South America formed in this way. The Andes continue to grow higher due to the ongoing subduction of Nazca Plate beneath the South American Plate. As the Nazca Plate is pulled downward, its marine sediments are scraped off onto the granitic roots of the Andes. This material adds thickness and buoyancy to the mountains, which allow the Andes to rise upward more rapidly than they are eroded by wind and rain.

Conclusion:

Therefore, subduction is the driving force for mountain building in the Andes.