Peru–Chile "Atacama" Trench (South America)

Peru–Chile "Atacama" Trench (South America)

Wed, 10/23/2019 - 11:21

The Peru–Chile Trench, also known as the Atacama Trench, is an oceanic trench in the eastern Pacific Ocean off the coast of Peru and Chile. It delineates the boundary between the subducting Nazca Plate and the overriding South American Plate.

Peru-Chile "Atacama" Trench

The Peru-Chile Trench, also known as the Atacama Trench, is an oceanic trench in the eastern Pacific Ocean, about 160 km (100 mi) off the coast of Peru and Chile.

Oceanic trenches are topographic depressions of the sea floor, relatively narrow in width but very long. These oceanographic features are the deepest parts of the ocean floor. Sediments within the trench are alternate layers of turbidites and oceanic deposits (mainly clays, volcanic ash, and siliceous oozes).

The Peru-Chile Trench reaches a maximum depth of 8,065 m (26,460 ft) below sea level in "Richards Deep" and is approximately 5,900 km (3,666 mi) long. Its mean width is 64 km (40 mi) and it covers an expanse of some 590,000 sq km (228,000 sq mi).

The eastern margin of the Nazca Plate is a convergent boundary subduction zone under the South American Plate and the Andes Mountains, forming the Peru–Chile Trench. Two seamount ridges within the Nazca Plate enter the subduction zone along this trench: the Nazca Ridge and the Juan Fernández Ridge.

Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced to sink due to high gravitational potential energy into the mantle.

Diagram of the geological process of subduction
Diagram of the geological process of subduction


The subduction of the Nazca Plate below the South American Plate along the trench is associated with numerous earthquakes.

The Peru–Chile Trench, the forearc, and the western edge of the central Andean plateau (Altiplano), delineate the dramatic "Bolivian Orocline" that defines the Andean slope of southern Peru, northern Chile and Bolivia.

The Bolivian Orocline is a seaward concave bending in the coast of South America and the Andes mountains at about 18° S. At this point the orientation of the Andes turns from Northwest in Peru to South in Chile and Argentina.

Most of the time, the trade winds drive surface waters offshore near the equator, driving the Humboldt Current from the tip of southern Chile to northern Peru.

This current is associated with upwelling of deep, nutrient-rich water off the coast of Peru. At times, El Nino disrupts the usual wind pattern and lessens the upwelling. The consequent loss of nutrient causes fish kills.