Deep Ocean Trenches: Formation & Examples

Chelsie Wheeler, Christopher Cowan
  • Author
    Chelsie Wheeler

    Chelsie has been a private tutor and a peer mentor throughout her ten-year career as an environmental and fisheries biologist. She also has experience educating the public through various programs via outreach with presentations, festivals, and set courses. She has a bachelor of science degree in environmental management from Columbia Southern University and a master of science degree in coastal and marine environments from the University of Ireland, Galway.

  • Instructor
    Christopher Cowan

    Christopher has taught Environmental Science and has trained employees about environmental compliance and worker safety. He has a Master's degree in Environmental Science.

How are ocean trenches formed? Learn how the movement of tectonic plates form the deep ocean trenches and see examples of some of the more famous trenches. Examine how life still thrives in the deep ocean trenches and how vital that life is to understanding human evolution. Updated: 08/14/2021

Table of Contents


Ocean Trench Definition

An ocean trench is a deep indent in the surface floor of the ocean and is the deepest part of the ocean. Trenches are located in subduction zones at or near a convergent boundary, continental crust, and/ or volcanic islands. The Mariana Trench is the deepest known trench globally, located more than 35,000 feet below sea level. The hadal zone is the zone associated with the area at the bottom of the ocean where trenches are found.

The Mariana Trench is the deepest known area in the ocean.

Ocean Trench

How are Trenches Formed

The earth's surface comprises tectonic plates, which are sections of the earth's crust that move and change. Ocean trenches are formed when:

  1. Old and heavy tectonic plates collide with new plates
  2. The heavy plates are pushed below the new and light plates, and this push causes the indent to occur, a process called subduction and can create a subduction zone. This is a type of convergent plate boundary meaning where plates converge, which is one of three processes when plates come together.

The push of volcanic material results in the formation of islands and causes large earthquakes. Earthquakes caused by subduction are some of the largest in the world, even when compared to terrestrial earthquakes, and can happen anywhere a subduction zone is present. These large earthquakes can sometimes even ripple out and be the cause of major tsunamis. The volcanic material in lower levels of the trenches can feed certain organisms as well. While crust is being pulled down below the trenches, it causes a deeper hole to form on the outer surface, causing the trenches to be bottomless. We can measure the depth of the ocean using a process called bathymetry. There are two main layers of the mantle involved in the process of subduction, which is the lithosphere and asthenosphere. The lithosphere is the upper layer of the mantel and consists of the tectonic plates. In contrast, the asthenosphere is the lower layer of the mantel and consists of lava and rock at very high temperatures from the earth's core.

Natural Process Cause Effect
Underwater Volcanoes The push of volcanic material from the asthenosphere into the lithosphere. • formation of islands
• earthquakes
• subduction
• feeding of benthic organisms
Underwater Earthquakes • movement of tectonic plates
• push of volcanic material into the lithosphere
• subduction

Trenches are formed at subduction zones on a convergent plate boundary.

Trench Diagram

Where are Trenches Found

Trenches are found on the floor of the sea; however, their common name is deep ocean trenches because they are more often found in the deepest areas of the ocean. Trenches are formed in subduction zones where tectonic plates collide. There are many known trenches that scientists continue to study. Some examples of these include:

  1. the Mariana Trench
  2. the Tonga Trench
  3. the Philippine Trench

All three trenches are located within the Ring of Fire, also known as the circum-Pacific belt, where most of the earth's volcanoes are. This area also has an increased risk of earthquakes and a large majority of high mountain ranges.

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  • 0:04 Definition of an Ocean Trench
  • 0:33 Formation of an Ocean Trench
  • 2:17 Location of Ocean Trenches
  • 3:32 Life in Ocean Trenches
  • 4:24 Lesson Summary
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Trench Location Depth General Facts
The Mariana Trench Situated between the Philippine and Pacific plates in the Pacific Ocean between Asia and Hawaii, just off the coast of Guam. Measured at over 35,000 feet deep. It is the deepest known trench in the world. Home of the Challenger Deep, a robotic scientific exploration vessel used to study the Mariana Trench.
The Tonga Trench Located off the coast of Tonga, in the Pacific Ocean near Australia. It is the second deepest trench in the world at over 35,000 feet deep. The Horizon deep, a nickname given to the deepest spot in the Tonga Trench.
The Philippine Trench Located off the coast of the Philippines in the Pacific Ocean between Asia and Australia. It is the third deepest trench in the world at over 34,000 feet deep. It was formed when the Palawan and Zamboanga plates collided around 8-9 million years ago.

The Ring of Fire is where the majority of the earth

Ring of Fire

What Happens in Deep Ocean Trenches

The deeper you go into the ocean, light, oxygen, and food sources start to dwindle. Diversity is high, but the amount of living organisms is low. However, even with these fundamental requirements for life being scarce, organisms have been able to adapt. Many deep-sea organisms have evolved to live in areas where other organisms cannot. They can do this by using tools such as bioluminescence, feeding on carbon instead of oxygen, and dwelling near hot vents that release nutrients into the water column.

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Frequently Asked Questions

What is the deepest trench in the ocean?

The Mariana trench located off the coast of Aisa is the deepest trench in the world; it is recorded as being over 35,000 feet deep.

What is the meaning of ocean trenches?

An ocean trench is a deep indent in the surface floor of the ocean and makes up the deepest parts of the ocean.

Are ocean trenches divergent?

Ocean trenches cannot be divergent; however, there are three types of boundaries that explain the process of two tectonic plates coming together or separating. These different boundaries include 1) divergent, 2) transform, and 3) convergent. Ocean trenches are convergent, meaning they come together.

How ocean trenches are formed?

Trenches are formed in subduction zones where tectonic plates collide, and the old sediment is pushed down below the new sediment, which causes a ditch to form.

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