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8.2: Volcanic Eruptions

Difficulty Level: At Grade Created by: CK-12
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Lesson 8.2: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. The 1985 Mount St. Helens eruption was the biggest volcanic eruption that ever occurred.

_____ 2. All volcanic eruptions involve explosions.

_____ 3. A volcanic eruption may be more powerful than a nuclear explosion.

_____ 4. Gases form in a volcano when magma boils and evaporates.

_____ 5. Ash from a volcanic eruption may stay in the atmosphere for years.

_____ 6. Gases from a volcano may cause environmental problems.

_____ 7. A volcano is more likely to be explosive when lava is thin and runny.

_____ 8. When a’a lava cools, it forms lava tubes.

_____ 9. Pillow lava is especially common along mid-ocean ridges.

_____ 10. A volcano’s history can help scientists predict whether the volcano is likely to erupt again.

Lesson 8.2: Critical Reading

Name___________________ Class______________ Date________

Read this passage based on the text and answer the questions that follow.

Types of Volcanic Eruptions

Volcanic eruptions can be explosive or non-explosive. Only rarely do explosive and non-explosive eruptions happen in the same volcano.

Explosive volcanic eruptions generally occur when magma is thick and doesn’t flow easily. It may block the vent of a volcano, allowing a buildup of gases. Gas pressure grows until the volcano erupts in an explosion. Explosive volcanic eruptions can be thousands of time more powerful than an atomic bomb. Ash and other particles from the eruption may form a mushroom cloud, like the cloud formed by a nuclear explosion. Chunks of the volcano fly high into the atmosphere. Hot fragments of rock, called pyroclasts, fly up into the air at very high speeds and cool in the atmosphere. Huge clouds of ash and particles may shoot many kilometers into the sky. Some of the ash may stay in the atmosphere for years. It may block out sunlight, change weather patterns, and affect Earth’s temperature. Gases from the eruption can form poisonous, invisible clouds. The poisonous gases may be toxic to living things located close to the volcano. Farther away from the volcano, the gases may cause environmental problems such as acid rain and ozone destruction.

Non-explosive volcanic eruptions generally occur when magma is thin and flows easily. Lava flows out of the volcano, rather than blocking the vent, and little or no gas forms inside the volcano. The lava simply pours out and flows over the ground like a river. People generally have a lot of warning before a lava flow like this reaches them, so non-explosive eruptions are much less deadly. However, they may destroy property as it becomes covered with lava.


  1. What factors lead to an explosive volcanic eruption?
  2. Describe what happens during an explosive volcanic eruption.
  3. What are some long-term effects that an explosive volcanic eruption may cause?
  4. When is a volcanic eruption likely to be non-explosive?
  5. Describe a non-explosive volcanic eruption.
  6. Why is a non-explosive eruption less likely than an explosive eruption to cause deaths?

Lesson 8.2: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. Which statement about Mount St. Helens is false?
    1. It is an active volcano.
    2. Its 1980 eruption was explosive.
    3. It is unlikely to erupt again.
    4. all of the above
  2. Compared with the solid rock around it, magma is
    1. cooler.
    2. harder.
    3. less dense.
    4. two of the above
  3. The deepest magma chambers are about
    1. 16 km below the surface.
    2. 160 km below the surface.
    3. 1600 km below the surface.
    4. 16,000 km below the surface.
  4. A non-explosive volcanic eruption may release a large quantity of
    1. ash.
    2. gases.
    3. molten rock.
    4. pyroclasts.
  5. The chemistry of magma determines
    1. how it erupts.
    2. how thick it is.
    3. what type of igneous rock it forms.
    4. all of the above
  6. For magma to form, solid rock must reach a temperature of at least
    1. 600 °C.
    2. 1600 °C.
    3. 6000 °C.
    4. 16,000 °C.
  7. Signs that a volcano may soon erupt include
    1. earthquakes.
    2. ground tilting
    3. release of gases.
    4. all of the above

Lesson 8.2: Matching

Name___________________ Class______________ Date________

Match each definition with the correct term.


_____ 1. thickest type of non-explosive lava

_____ 2. volcano that has not erupted in recent history and probably will not erupt again

_____ 3. region within Earth that is surrounded by solid rock and contains magma

_____ 4. hot volcanic rock thrown into the air by an explosive eruption

_____ 5. lava that enters water

_____ 6. any release of magma onto Earth’s surface

_____ 7. volcano that has erupted in recent history and probably will erupt again


a. magma chamber

b. volcanic eruption

c. pyroclast

d. a’a

e. dormant volcano

f. pillow lava

g. extinct volcano

Lesson 8.2: Fill in the Blank

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

  1. The type of volcanic eruption that occurs when gases build up in a volcano is a(n) __________ eruption.
  2. When magma or lava cools, it forms __________ rock.
  3. Thick lava may block the vent of a volcano and result in a(n) __________ eruption.
  4. Pāhoehoe lava is __________ than a’a lava.
  5. __________ are Earth scientists who specialize in the study of volcanoes.
  6. A(n) __________ volcano is a volcano that is currently erupting or showing signs that it will erupt soon.
  7. Magma collects in __________ beneath Earth’s surface.

Lesson 8.2: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Why is it important to predict volcanic eruptions? Identify factors that scientists use to predict eruptions.

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