9.53 Shield Volcano Facts

You’ve probably seen a picture of a tall, explosive volcano, but you might mistake this volcano for a low mountain. A shield volcano has long, gently sloping sides and a lava flow that spills, instead of explodes.

What is a Shield Volcano?

Let’s say your teacher assigns you a project that involves building a volcano. How fun! You race home, sit down with a pile of clay, and start shaping your volcano into a tall, steep peak. It looks great, and you can’t wait to show it to your teacher, but before you can get a container to hold your masterpiece, tragedy strikes as the walls of your volcano collapsed! Your tall, thin volcano is now a low, dome-shaped volcano. Do you know how you can still earn an A on your assignment? Tell your teacher you made a shield volcano!

Shield volcanoes are found all over the world; in fact, the main islands of Hawaii are giant shield volcanoes that formed under the water.

What Do They Look Like?

A shield volcano has long, gently sloping sides. If you look at one from the land, you might think it looks like a low mountain or high hill. If you were to fly over the top of one, you might think it looks like a warrior’s shield, which is how this volcano got its name.

This shield volcano in the Galapagos Islands looks like a low mountain.
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Shield volcanoes might not be tall, but they are wide. The width of a shield volcano is often about 20 times its height. This flattened shape is due, in part, to the watery lava, or hot molten rock, that flows out of them.

The lava flow from this shield volcano looks like a red river.
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Because the lava is not very thick, it tends to run out in all different directions. Think of a shield volcano’s lava as milk spilling from a glass, and lava from other volcanoes as slow-flowing molasses. The fluid lava can travel a longer distance before it cools and hardens, which keeps it from piling into tall mounds.

1. Main points:

A shield volcano has a wide, dome-like shape with gently sloping sides, resembling a warrior’s shield, and is characterized by fluid lava that flows easily, preventing the formation of tall peaks.

2. Questions:

• Content Analysis: What are the main characteristics of a shield volcano’s shape and lava flow?
• Contextual Analysis: How does the nature of a shield volcano’s lava contribute to its unique shape?
• Semiotic Analysis: Why is it called a "shield" volcano?

3. Further Discussion:

• If you could visit a shield volcano, what would you like to observe and why?

4. Answers:

• Content Analysis: "A shield volcano has long, gently sloping sides… The width of a shield volcano is often about 20 times its height."
• Contextual Analysis: "Because the lava is not very thick, it tends to run out in all different directions… The fluid lava can travel a longer distance before it cools and hardens, which keeps it from piling into tall mounds."
• Semiotic Analysis: "If you were to fly over the top of one, you might think it looks like a warrior’s shield, which is how this volcano got its name."

Eruptions

Another reason for the flattened shape of a shield volcano is the way it erupts. When you think of a volcano, you likely think of a tremendous explosion that spews red, hot rocks and ash high into the sky. That is not a typical shield volcano eruption.

An erupting shield volcano
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You could say that the low-lying shield volcanoes are laid back when it comes to erupting because they rarely have explosive eruptions. Instead, lava flows from the volcanoes over a long period, much like an overflowing cup. The shield volcano might also ooze lava out of vents or cracks in the volcano walls. Because the lava flows out over time, it can travel far along the ground creating the long, gently sloping walls that characterize this type of volcano.

1. Main points:

Shield volcanoes have a flattened shape due to their non-explosive eruptions, where lava flows out slowly over time, creating long, gently sloping walls.

2. Questions:

• Content Analysis: How do shield volcano eruptions differ from typical explosive volcano eruptions?
• Contextual Analysis: Why does the slow lava flow of shield volcanoes contribute to their distinctive shape?
• Thematic Analysis: What are the key features of a shield volcano eruption?

3. Further Discussion:

• If you could compare the lava flow of a shield volcano to something in your daily life, what would it be and why?

4. Answers:

• Content Analysis: "They rarely have explosive eruptions. Instead, lava flows from the volcanoes over a long period, much like an overflowing cup."
• Contextual Analysis: "Because the lava flows out over time, it can travel far along the ground creating the long, gently sloping walls that characterize this type of volcano."
• Thematic Analysis: "The shield volcano might also ooze lava out of vents or cracks in the volcano walls."

Lesson Summary

A shield volcano has long, gently sloping sides that resemble a warrior’s shield. Shield volcanoes do not have explosive eruptions; instead, a watery lava flows from the volcano over a long period, which allows the lava to travels long distances before it cools and hardens.