Summary

This video describes the three types of plate boundaries and provides examples of each. It continues to explain how mountains and trenches are formed from these boundaries. In addition, the concept of subduction zones is also explained.

Why Watch This Video?

Have you ever wondered how mountains are formed?

Would you like to know how ocean crust is recycled?

Have you ever been confused by Earth’s different plates and how they move?

Key Terms

Mid Ocean Ridge – a ridge on the seafloor formed by plate tectonics that contributes to the formation of new seafloor by magma coming up through the ridge

Subduction zones – at a plate boundary, the region where one plate is forced underneath the other plate, and triggering melting in the mantle. It is how crust is recycled.

Lithosphere – layer made up of the crust and upper-most mantle. Lithosphere is what makes up tectonic plates.

Loose Ends

During a continent-continent collision, why does one continental plate go under the other continental plate even though they have the same properties?

Because the plates have the same properties, one is not subducted under the other but instead the plates collide and go upwards forming mountains. There can still be parts of the plates hanging downward, even if there isn’t actually a subduction zone, and those portions of the plates can eventually break off after the collision and sink into the mantle. The diagram included in the video of continent-continent collision provides a confusing image as it makes it seem very similar to the other types of collisions where plates are subducted.

 How long did it take the Himalayas mountains to form?

They began forming about 40-50 million years ago. However, they are still continuing to be made by continental-continental collision daily.

 Why do Earth’s plates move?

Proposed forces of tectonic plate movement:

Mantle convection currents – mantle currents carry plates along like a conveyor belt

Ridge push – newly formed plates at oceanic ridges are warm and have a higher elevation than the colder plates, through gravitational forces, the oceanic lithosphere slides down the asthenosphere and moves farther away from the ridge

Slab pull – older, colder plates sink at subduction zones
as plates cool, they become more dense, the cooler plate pulls the rest of the warmer plate along behind it

Most of the force behind plate motion is thought to be the result of slab pull.

Source: British Geological Survey. (2020). What drives the movement of tectonic plates? https://www.bgs.ac.uk/discoveringGeology/hazards/earthquakes/whatDrivesTectonicPlates.html

Self-Test Questions

Scroll down for the answers.

1. Which of these are NOT a type of plate boundary?

1. Convergent
2. Subduction
3. Divergent
4. Transform

2. How deep is The Mariana Trench?

1. 103 km
2. 20 km
3. 22 km
4. 11 km

3. What type of plate boundary runs through the middle of Iceland?

1. Convergent
2. Subduction
3. Divergent
4. Transform

4. What type of plate boundary contains subduction zones?

1. Convergent
2. Divergent
3. Transform
4. Double

5. What plates form the plate boundary of the Andes mountains?

1. South American Plate and Scotia Plate
2. Nazca Plate and Cocos Plate
3. Pacific Plate and South American Plate
4. Nazca Plate and South American Plate

Answers

1. b. Subduction. The three types of plate boundaries are convergent, divergent and transform. Subduction occurs along some convergent boundaries, but is not itself a type of boundary. It is a way of recycling oceanic crust.

2. d. 11 km. The Mariana Trench is off the coast of Japan and is the deepest trench in the world.

3. c. Divergent. A divergent plate runs through the middle of Iceland pulling apart the North American Plate and the Euroasian Plate, producing volcanic eruptions.

4. a. Convergent. Plates are coming together at this type of boundary which forces one plate to go underneath the other, forming a subduction zone

5. d. Nazca Plate and South American Plate. These plates converge together in an continent-oceanic crust collision to create the Andes mountains in South America through subduction.