Peru-Chile Trench: The World's Longest Ocean Trench

The Peru-Chile Trench (also called the Atacama Trench) is a 5,900-kilometer-long oceanic trench running parallel to the western coast of South America from southern Panama to the Chiloé Archipelago of southern Chile. It is the longest ocean trench in the world, reaching a maximum depth of 8,065 m at the Richards Deep off northern Chile. The trench marks the convergent boundary where the Nazca Plate (oceanic) is being subducted beneath the South American Plate (continental) at a rate of approximately 6.6 cm per year — a process that has built the Andes mountains, generated the largest earthquake ever instrumentally recorded (the 1960 Valdivia earthquake at magnitude 9.5), and continues to produce some of the most powerful seismic events on Earth.

Introduction

While the Mariana and Tonga trenches are deeper, no ocean trench in the world is longer than the Peru-Chile Trench. Its length matters geologically because subduction along its full extent has been the principal force building the Andes — the world's longest continental mountain range — over the past 200 million years. The trench-Andes system is also the source of three of the seven largest earthquakes ever recorded: the 1960 Valdivia (M9.5, Chile), the 2010 Maule (M8.8, Chile), and the 1868 Arica (M8.8–9.1, Peru/Chile). Combined with the dry Atacama Desert directly inland (built by the Humboldt Current along this same coast), the Peru-Chile Trench represents one of the most distinctive geographic systems on Earth.

Geography & Depth

• Length: Approximately 5,900 km — the longest ocean trench in the world
• Width: 60 km average
• Maximum depth: 8,065 m at Richards Deep (off northern Chile)
• Location: Pacific Ocean, parallel to the Pacific coast of South America
• Span: From southern Panama (~3°N) south to the Chiloé Archipelago of Chile (~43°S)

The Peru-Chile Trench parallels the South American coast, lying offshore from southern Panama, Colombia, Ecuador, Peru, and Chile. Its deepest point, Richards Deep at 8,065 m, lies off northern Chile near the city of Antofagasta. The trench is generally narrower and somewhat shallower than the Pacific Ocean's western trenches because the subducting Nazca Plate is younger (and therefore less dense and slightly more buoyant) than the older Pacific Plate slabs subducting along the Mariana, Tonga, and Kuril trenches.

Plate Tectonics & Andes Formation

• Subducting plate: Nazca Plate (oceanic, relatively young)
• Overriding plate: South American Plate (continental)
• Convergence rate: 6.6 cm/year
• Andes uplift: Active for ~200 million years; current rates 2–10 mm/year

The Peru-Chile Trench-Andes system is the textbook example of "Andean-type" subduction: an oceanic plate descending beneath a continental margin, building a continental volcanic arc and a major mountain range over geologic time. The Nazca Plate has been subducting beneath South America for approximately 200 million years, with active mountain-building producing the modern Andes over the past 60–80 million years. The subduction angle varies along the trench: in central Peru and central Chile, the Nazca slab descends at a steep angle (~30°) and produces a clear volcanic arc; in northern Peru and central Chile/Argentina (south of the volcanic arc gap), the slab subducts shallowly ("flat slab") and suppresses volcanism while pushing up a wider mountain belt. The Andes reach 6,961 m at Aconcagua — the highest point in the Western and Southern Hemispheres.

Major Earthquakes

• 1960 Valdivia earthquake (Chile): M9.5 — the largest instrumentally-recorded earthquake in history
• 1868 Arica earthquake (Peru/Chile): M8.8–9.1
• 1877 Iquique earthquake (Chile): M8.8
• 2010 Maule earthquake (Chile): M8.8
• 2014 Iquique earthquake (Chile): M8.2
• 2007 Pisco earthquake (Peru): M8.0

The Peru-Chile Trench has produced more major earthquakes (magnitude 8.0+) in the instrumental record than any other subduction zone except possibly the Sumatra-Andaman (Java) Trench. The 1960 Valdivia earthquake remains the largest earthquake ever instrumentally recorded — magnitude 9.5, with seismic moment release equivalent to about 26% of all earthquake energy released worldwide during the entire 20th century. The Valdivia rupture extended along approximately 1,000 km of the trench and triggered a Pacific-wide tsunami that caused damage as far away as Hawaii, Japan, and the Philippines. The 2010 Maule earthquake occurred at almost exactly the northern end of the 1960 rupture zone, releasing strain that had been accumulating for the previous 50 years.

Marine Life & Hadal Biology

• Atacama Hadal Zone: The trench's deepest sections explored by submersible
• Endemic species: Snailfish, polychaete worms, amphipods adapted to extreme pressure
• Humboldt Current overlay: The world's most productive marine ecosystem sits above the trench

The waters above the Peru-Chile Trench are some of the most biologically productive on Earth — sustained by the Humboldt Current's coastal upwelling, which pulls nutrient-rich deep water to the surface. The Peruvian anchoveta fishery alone produces roughly 6 million tonnes of catch per year (in good years), making it one of the world's largest single-species fisheries. The trench itself, however, is biologically isolated from the productive surface waters; its hadal-zone (>6,000 m) ecosystem includes endemic snailfish species, amphipod crustaceans, and polychaete worms adapted to crushing pressures, total darkness, and minimal food input.

Connection to the Atacama Desert

• Atacama Desert: World's driest non-polar desert, immediately east of the trench
• Mechanism: Cold Humboldt Current along the trench cools coastal air, suppresses convection, prevents rainfall
• Rainfall: Under 15 mm/year on average across the Atacama; some weather stations have gone over a decade without measurable rain

The Peru-Chile Trench has a striking geographic association with the Atacama Desert directly inland. Cold deep water carried north along the trench by the Humboldt Current cools the air above the coastal Pacific. This cool air, sliding inland against the Andean uplift, produces a strong temperature inversion that suppresses convection and rainfall. The result — combined with the Andean rain shadow blocking moisture from the Atlantic — is the driest non-polar desert on Earth. The Atacama Trench (an alternate name for the Peru-Chile Trench in its central Chilean section) and the Atacama Desert thus form a single coupled geographic system.

Key Facts

• The Peru-Chile Trench is the longest ocean trench in the world at approximately 5,900 km
• It reaches 8,065 m at Richards Deep — its deepest point — off northern Chile
• The 1960 Valdivia earthquake along this trench is the largest earthquake ever instrumentally recorded (M9.5)
• Subduction along this trench has built the Andes — the world's longest continental mountain range
• The Atacama Desert directly inland is created by the cold Humboldt Current that flows above the trench

Frequently Asked Questions

What is the Peru-Chile Trench?

The Peru-Chile Trench (also called the Atacama Trench) is a 5,900 km-long oceanic trench in the Pacific Ocean, running parallel to the western coast of South America. It is the longest ocean trench in the world and marks the convergent boundary where the Nazca Plate is being subducted beneath the South American Plate at ~6.6 cm per year — the process that built the Andes mountains.

How deep is the Peru-Chile Trench?

The Peru-Chile Trench reaches a maximum depth of 8,065 m at Richards Deep, off northern Chile near the city of Antofagasta. While it is not the deepest ocean trench (the Mariana Trench reaches 10,925 m), it is the longest at approximately 5,900 km. Average depth across the trench is around 5,000–6,000 m.

What is the Atacama Trench?

The Atacama Trench is an alternate name for the Peru-Chile Trench, particularly in its Chilean section. The name highlights the geographic association with the Atacama Desert directly inland — the world's driest non-polar desert, which is created in part by the cold Humboldt Current flowing above the trench. The trench and desert form a single coupled climatic and geological system.

How did the Peru-Chile Trench create the Andes?

The subduction of the Nazca Plate beneath the South American Plate has been ongoing for approximately 200 million years. As the oceanic Nazca Plate descends, it releases water that triggers melting in the overlying mantle, producing volcanic arcs along the western edge of South America. Compression also crumples and uplifts the continental crust. Over time these processes have built the Andes — the world's longest continental mountain range, peaking at Aconcagua (6,961 m).

What was the 1960 Valdivia earthquake?

The 1960 Valdivia earthquake was a magnitude 9.5 rupture along the Peru-Chile Trench off central-southern Chile — the largest earthquake ever recorded by modern seismic instruments. It killed an estimated 1,000–7,000 people in Chile, triggered a Pacific-wide tsunami that caused damage in Hawaii (61 deaths), Japan (138 deaths), and the Philippines, and released seismic energy equivalent to about 26% of all earthquake energy released worldwide during the entire 20th century.

Final Thoughts

The Peru-Chile Trench is the master geological feature of South America — the engine that built the Andes, the source of the world's largest earthquakes, and the cold-water highway that creates the Atacama Desert. As the longest ocean trench on Earth, it is a defining feature of the planet's plate-tectonic geography.