Week 5 - Converging Plates - Kyle Quirk

This week I decided to visit the Andes Mountains in South America, where the South American plate and Nazca plate meet.  This convergent plate boundary is a subduction zone, with the more dense Nazca plate sinking under the South American plate.  This plate boundary is marked on the ocean floor by the Atacama Trench just to the west of South America.

Atacama trench, photo courteous of futura-sciences.com

The collision of these two plates causes the leading edge of the South American plate to deform by folding the rock.  This increases the vertical thickness of the South American plate, at the same time reducing the width of the lithosphere.  This interaction is what created the fold mountains of the Andes.

Andean volcanoes such as the strato-volcano Lascar, in Chile, are a good example of the continued subduction of the Nazca Plate.  This
type of subduction causes water that was locked in the oceanic crust to heat up, which lowers the melting point of the mantle.  This produces magma, which will rise and possibly explosively erupt as andesitic magma.  These volcanoes will produce ash and pyroclastic flows as well as small amount of lava.

Lascar volcano in Chile, photo provided by Wikipedia