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Subduction: Definition & Process

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  • 0:00 What Is Subduction?
  • 0:39 The Process Of Subduction
  • 2:18 Subduction And Volcanoes
  • 3:15 Examples Of Subduction Zones
  • 4:01 Lesson Summary
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Lesson Transcript
Instructor
Mary Ellen Ellis
Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

Subduction is a geological term for one of Earth's tectonic plates sinking under another. When this happens, we can get earthquakes, volcanoes, and a recycling of Earth's rocks. Let's explore this more in this lesson.

What Is Subduction?

Subduction is a kind of geological recycling. It occurs at convergent tectonic plate boundaries or where two tectonic plates come crashing together, in slow motion of course. At a convergent boundary, two plates can come together and rise up into mountains. This is how the impressive Himalayan Mountain range formed when India crashed into the rest of Asia. Another possibility for a convergent boundary is subduction. Instead of both plates crumpling upwards to form mountains, one sinks under the other and is recycled back into the mantle.

Subduction occurs when one plate sinks under another and is recycled into a deep layer of the mantle, called the asthenosphere.
subduction

The Process of Subduction

As you know, the earth's crust is not continuous but divided up into pieces, like a puzzle. These pieces, the tectonic plates, move around relative to each other, powered by circular convection cycles in the fluid mantle, a layer beneath the crust. Some plates move sideways past each other, some pull apart from each other, and others come together. The latter are convergent plates.

In a region in which one of two convergent plates sinks under the other, we call it a subduction zone. A tectonic plate is made of both crust, or the outer layer of the earth, and a thin upper layer of the mantle. Together, these two layers are called lithosphere. The two tectonic plates and the lithosphere involved in a subduction zone may both be oceanic, or one may be oceanic and the other continental.

When an oceanic lithosphere meets a continental lithosphere in a subduction zone, the oceanic plate always goes under the continental plate. This is the rule because the rock making up an oceanic lithosphere is denser than in a continental lithosphere. When two oceanic plates come together, one may sink under the other.

The mantle underneath the lithosphere is hot, fluid rock. When one plate sinks into it during subduction, it melts into the mantle. Essentially, the rock making up that plate is getting recycled. New plates form at tectonic boundaries that are diverging. At these boundaries, usually under the ocean, two plates pull apart and magma wells up and hardens, forming new rock and crust.

Subduction and Volcanoes

The movement of one plate under another and the recycling of rock into magma can lead to some exciting geologic activity. Deep earthquakes can occur as the two plates rub against each other and release energy, but they are not as common or as devastating as the earthquakes that occur at other types of plate boundaries. More interesting is the formation of volcanoes in subduction zones.

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Additional Activities

Subduction Word Scramble Activity

For this activity, study the scrambled letters and try to unscramble or rearrange the letters to form a word or phrase that fits the given clues. To do this, you must right-click and print this page. With a pencil and an eraser, neatly write your answers in the blank space provided.

Scrambled Words

_________________________1. NCVNEREOTG NIDBRUSOAE

_________________________2. MELNAT

_________________________3. ADLINS RCA

_________________________4. CINOACE EPLTA

_________________________5. MAALHSIAY

_________________________6. SOTNDBIUCU

_________________________7. ECITTCON ELTAP

_________________________8. TICOCENONV

_________________________9. LEHOTPESIHR

_________________________10. CLIVONCA CAR

Clues

  1. These are areas of compressive stress and, depending on the nature of the plate interactions, the recycling or destruction of the lithosphere.
  2. It is known as the Earth's thickest layer where rocks flow without breaking.
  3. A long chain of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries.
  4. This plate sinks when an oceanic lithosphere meets a continental lithosphere in a subduction zone.
  5. The continental-continental collision of India with Asia produced, and is still producing, this mountain range.
  6. Pertains to the process in which one plate bends and descends beneath the other.
  7. It is made of both crust, or the outer layer of the earth, and a thin upper layer of the mantle.
  8. The transmission of heat in the mantle by the circulation of currents.
  9. The rigid, mechanically strong, outer layer of the Earth, including the entire crust and the uppermost part of the mantle.
  10. Refers to a chain of volcanoes formed from continent-oceanic interactions.


Answers

  1. CONVERGENT BOUNDARIES
  2. MANTLE
  3. ISLAND ARC
  4. OCEANIC PLATE
  5. HIMALAYAS
  6. SUBDUCTION
  7. TECTONIC PLATE
  8. CONVECTION
  9. LITHOSPHERE
  10. VOLCANIC ARC

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