The Nazca bowl is moving eastwards, in the direction of the south American Plate, at about 79mm every year.
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Where the 2 plates meet, the denser oceanic lithosphere the the Nazca bowl is required down and under the an ext buoyant continent lithosphere that the south American Plate, descending in ~ an angle into the mantle in a process called subduction. This is marked on the ocean surface by the presence of the Peru-Chile (or Atacama) Trench.
The friction in between the plates prevents the subducting oceanic key from slide smoothly. As it descends, the drags against the overlying plate, leading to both to fracture and deform. This results in frequent shallow emphasis earthquakes that get deeperas the s plate descends further, defining a zone that earthquake foci recognized as a Benioff zone.
As subduction that the Nazca bowl continues, several of the sediments that accumulated on the ocean floor (together with several of the s crust) room scraped off and also forced (accreted) onto the south American key in a process called “obduction”. This forms an accretionary wedge (or ‘prism’), whereby layers that the deformed and metamorphosed sediments and also ocean crust are thrust ~ above the southern American Plate follow me faults – or thrust plane – including to the dimension of the continent.
Cross section of an accretionary wedge
Image: Fromwww.searchanddiscovery.com ‘Deepwater Fold-Thrust Belts: no All the Beasts space Equal’, Ana Krueger and Ed Gilbert, 2009
The effect of the collision of the two plates deforms the top edge the the southern American bowl by urgent the rocks. This crustal shortening increases the vertical thickness whilst reducing the broad of the lithosphere in the collision region (imagine a vehicle hitting a heavy wall) and also so produces the fold hills of the Andes.
Continued subduction that the Nazca Plate brings sea water, locked in the s crust, deep right into the mantle. As the bowl heats up the water is liberated, lowering the melting suggest of the mantle and causing partial melting. This producesmagma, i m sorry rises and also maybe erupted explosively as andesite at the surface.
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Andesitic magma is less thick than the bordering material, and can have actually a temperature of 1000oC. That is viscous, trapping gases together it rises. The water and gases in andesitic magma account for the explosive task of andesitic volcanoes, which generally lie dormant for many hundreds or thousands of years. These volcanoes typically produce ash and pyroclastic flows, too as tiny amounts the andesitic lava.
Andean volcanoes such as the stratovolcanoLáscar, in northern Chile, area good example of this form of activity. Láscar erupted ash and also pyroclastic operation in 1993 and was still active in 2012.