9.34 How are Mountains Formed

Different types of mountains are formed when tectonic plates push and pull. Learn about mountain formation, the parts of the earth, and the types and formations of mountains.

Mountain Formation & Parts of the Earth

Mountains are both formed and destroyed by nature. The wind, rain, and ice are constantly breaking the mountains down and causing them to become smaller. However, new mountains are also constantly being formed. Although this formation is very gradual, it does happen over time.

The surface of the earth is just the top layer that we see. It includes the grass, soil, rocks, and pebbles that we seen and walk on. Directly under the surface is the earth’s crust. This is a very rocky layer of the earth. This layer is made up of over 50 tectonic plates, which are large stone bases that are constantly moving. These plates move to form the mountains.

Under the crust is a very solid rock layer, which is about 60 miles deep. Together, this layer and the crust make up a layer called the lithosphere.

1. Main points:

Mountains are formed and eroded by natural forces like wind, rain, and ice. The Earth’s surface includes the crust, made of over 50 tectonic plates that shift to form mountains. Below this is a solid rock layer, which together with the crust, constitutes the lithosphere.

2. Questions:

• Content Analysis: What natural forces contribute to the breaking down of mountains?
• Contextual Analysis: How does the movement of tectonic plates affect the Earth’s surface?
• Thematic Analysis: What are the layers of the Earth mentioned in the text?

3. Further Discussion:

• If you could explore any layer of the Earth, which one would it be and why?

4. Answers:

• Content Analysis: "The wind, rain, and ice are constantly breaking the mountains down."
• Contextual Analysis: "These [tectonic] plates move to form the mountains."
• Thematic Analysis: "Directly under the surface is the earth’s crust" and "Under the crust is a very solid rock layer…Together, this layer and the crust make up a layer called the lithosphere."

Think about how amazing it is that the ground we walk on is constantly changing, even if we can’t see it happening. If you could add another layer to the Earth, what would it be like?

Types & Formations of Mountains

There is not just one type of mountain, there are several types. Let’s talk about a few of them.

1. Dome Mountains

Dome mountains are formed when the magma, which is a hot layer of rock, pushes up through the lithosphere, causing the crust to bend up. This bend forms a dome shape, hence the name ‘dome mountains’.

2. Folded Mountains

Folded mountains are formed when two plates push into each other. The pressure of the two plates pushing against one another causes the crust to create lifts and folds over each other. One way to visualize this is to take a dish towel, spread it out on a flat surface and put one hand on each side of the towel. Push your hands towards each other slowly; you will see folds begin to form. That is how these types of mountains are formed.

3. Fault-Block Mountains

Sometimes the earth’s pressure causes the plates to pull and stretch. This pulling and stretching causes small cracks within the crust. As the cracks happen, some parts of the crust sink down, while other parts of the crust rise up. This forms what looks like rectangular blocks, which are fault-block mountains.

Check out this image appearing here:

In this diagram of a fault-block mountain, the left side has risen up, while the right has sunk down, creating what looks like rectangular blocks.

4. Volcanic Mountains

Volcanic mountains are formed when there is a small vent in the lithosphere, in the middle of a plate. This allows the hot magma to be pushed up and then cool. The ash cools, then it hardens, and a cone-shaped mountain forms. The build up of hardened ash is what causes the mountain to form.

These mountains can also be formed when one of the tectonic plates pushes into another, causing one of the plates to sink, and the friction between the two begin to heat up the magma. The magma finds a soft spot between the two plates and rises up through that spot. Mt. Saint Helens in Washington is a great example of this.

Mt. Saint Helens was created by lava and ash erupting from the top. It blew up again one day after this picture was taken.

1. Main points:

Mountains come in various types, including dome mountains formed by magma pushing the crust upwards, folded mountains created by the collision of tectonic plates, and fault-block mountains resulting from the crust being stretched and cracked.

2. Questions:

• Content Analysis: How are dome mountains formed?
• Contextual Analysis: What is the process that leads to the formation of folded mountains?
• Thematic Analysis: What unique feature characterizes fault-block mountains?

3. Further Discussion:

• If you could visit one of these types of mountains, which would it be and why?

4. Answers:

• Content Analysis: Dome mountains are formed when "magma…pushes up through the lithosphere, causing the crust to bend up."
• Contextual Analysis: Folded mountains are formed "when two plates push into each other…the crust to create lifts and folds over each other."
• Thematic Analysis: Fault-block mountains are characterized by "the earth’s pressure causes the plates to pull and stretch…some parts of the crust sink down, while other parts of the crust rise up."

Imagine being able to see these different types of mountains and how they form. Which one do you think would be the most amazing to see in person?

Lesson Summary

Okay, let’s review what we’ve learned about mountains and how they form. While the earth is made up of many layers, it’s the lithosphere, which is the combination of the crust and the deep rock layer, that impacts how a mountain is formed. The crust is simply a very rocky layer of the earth. The tectonic plates that are large stone plates on the crust that are constantly pushing and pulling, allow for new mountains to continue to form.

Some types of mountains that we can see due to this pushing and pulling of plates include dome mountains, which are formed when the magma pushes up through the lithosphere causing the crust to bend up; volcanic mountains, which are formed when there is a small vent in the lithosphere in the middle of a plate; fault-block mountains, which are formed when pulling and stretching causes small cracks within the crust and, as the cracks happen, some parts of the crust sink down while other parts of the crust rise up; and folded mountains, which are formed when two plates push into each other.