Convergent Boundary: Definition, Facts & Examples

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• 0:00 What Is a Convergent Boundary?
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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.

In this lesson, you will learn the meaning of the term 'convergent boundary' in the context of plate tectonics. A number of features and examples of convergent boundaries will be introduced. A short quiz will follow.

What is a Convergent Boundary?

Imagine the world is like an egg, with a shell that is cracked all over. Just like these cracked pieces of eggshell, the entire outer crust of the Earth is broken down into sections, called tectonic plates. But instead of resting on liquid-y egg yolk, these plates float on a sea of hot magma, something you'd only actually see in rare events like volcanoes. This magma is not a liquid - it's actually solid, but under the incredible pressures beneath the Earth's crust, even solids flow like honey.

The cracks in the egg are boundaries between plates. A convergent boundary, or destructive boundary, is where two plates are moving towards each other and colliding. The pressure and friction is great enough at these boundaries that the material in the Earth's mantle can melt, and both earthquakes and volcanoes happen nearby.

Features of Convergent Boundaries

When two plates meet, one inevitably gives way and sinks below the other. This is called subduction. The subduction zone is the area where two plates are sandwiched on top of each other, like a tectonic BLT. Exactly what happens during subduction depends on the type of tectonic plates involved. There are two kinds of plates: oceanic plates and continental plates.

Oceanic plates are exactly as they sound - the plates below the oceans. But they're defined not so much by the oceans, but by the material they're made of. Oceanic plates are made mostly of basalt and other mafic rocks. Continental plates are the part that lies above sea level, but again, the real definition is that the crust is made of granite and other felsic rocks.

When two continental plates collide, the impact is so significant that the material in the subduction zone is pushed upwards. This is how mountain ranges form, including even the biggest ones in the world, like the Himalayas.

When one oceanic and one continental plate meet, the denser oceanic plate subducts under the less dense continental plate. This forms a trench on the oceanic side, and volcanoes and mountains on the continental side.

When two oceanic plates meet, they form large trenches underwater. Material that is liquified under the pressure is pushed upwards, forming underwater volcanoes which can create islands.

Examples of Convergent Boundaries

The West Coast of South America is a convergent boundary between the Nazca Plate and the South American Plate. The collision of this oceanic and continental plate was how the Andes Mountains were formed.

Convergent boundaries can also form islands. The northern part of the Pacific Plate is subducting under the North American Plate, and the result is the formation of the Aleutian Islands.

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