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Subduction Zone: Definition, Location & Example

Subduction Zone: Definition, Location & Example
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  • 0:02 What Is a Subduction Zone?
  • 0:54 Features & Location
  • 2:46 Examples of Subduction Zones
  • 3:34 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

This lesson will discuss the meaning of the term 'subduction zone,' and where they occur in terms of tectonic plate boundaries. A few examples will be included, and a short quiz will follow.

What is a Subduction Zone?

The top layer of the Earth is called the crust. But as much as we like to think of the surface of the Earth as one continuous thing, it's not. The world is more like an egg shell, cracked all over. These sections of the Earth's crust are called tectonic plates, and they float on a sea of hot magma.

The crust of the Earth is broken into plates
The Crust of the Earth is Broken into Plates

The cracks in the egg are like boundaries between plates. There are three main types:

  1. Convergent boundaries, where plates move towards each other
  2. Divergent boundaries, where plates move apart
  3. Transform boundaries, where plates slide alongside each other.

A subduction zone is something that happens only with convergent boundaries. Subduction is where, after colliding, one plate sinks below the other. And a subduction zone is the area where two plates are sandwiched on top of each other, like a tectonic BLT.

Features & Location of Subduction Zones

Subduction zones are places of high activity. When two huge tectonic plates collide, the pressure and friction is great enough that the material in the Earth's mantle can melt, and both earthquakes and volcanoes can result.

The exact features around a subduction zone depend on the type of tectonic plates that are colliding. There are two kinds: oceanic plates and continental plates. Oceanic plates are, unsurprisingly, underneath the oceans. But this isn't what makes something an oceanic plate, because there are exceptions to this rule. Instead, an oceanic plate is a section of the Earth's crust that's made mostly of mafic or basaltic rock. In contrast, continental plates are composed of felsic or granitic rock.

Some subduction zones can be shorter-lived than others. If one of the two plates is oceanic, a full sandwich forms and can remain there indefinitely. However, two continental plates collide with such force that the material from each plate is broken up and forced upwards. This is why the biggest mountain ranges in the world form from the collision of two continental plates.

Oceanic Plate vs Continental Plate
Oceanic Plate vs Continental Plate

When one oceanic and one continental plate collide, the oceanic plate slides below the continental plate. This happens because oceanic rock is denser than continental. Features include an underwater trench on the oceanic side and mountains on the continental side.

Continental Plate vs Continental Plate

When two continental plates meet, the main feature that results is mountains. The Himalayas, the biggest mountain range in the world, was formed this way.

Oceanic Plate vs Oceanic Plate

Two oceanic plates collide to create large underwater trenches. The temperature and pressure can be so intense that it liquefies part of the crust, and this liquid rises up to create underwater volcanoes. These underwater volcanoes can form islands over long periods of time.

Examples of Subduction Zones

As mentioned previously, the Himalayas formed when two continental plates collided: the Eurasian Plate and the Indian Plate. This collision continues to this day - the Himalayas are still getting taller!

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