Gentle Flows, Violent Blasts

Science · Volcanoes & Earthquakes · ages 9-11

Name ______________________ Date ____________

Which type of eruption blasts ash and rock violently into the air?
- Effusive
- Explosive
- Extinct
Which type of eruption is a gentle lava flow?
- Effusive
- Explosive
- Dormant
Effusive eruptions produce violent blasts of ash and rock.
Circle one: True False
How can runny magma favor an effusive eruption?
- Gas escapes more easily
- The magma has no gas at all
- The volcano is extinct
Why can thick, sticky magma erupt explosively when it contains gas?
- It cools too quickly to erupt at all
- It has no gas in it at all
- Trapped gas builds pressure
The diagram shows a volcano's outline. Which description matches its shape?
- A wide shield volcano
- A steep cone volcano
- An extinct volcano
At an erupting volcano, magma resists flowing and holds many gas bubbles. What best describes its magma and possible eruption?
- Thick and gas-rich; it can explode
- It has no magma left
- It's thin and runny, causing effusive eruptions
Sam sees a broad shield volcano with gentle slopes. He says it must have been built mainly by thick, explosive magma. What is a better explanation?
- Wide volcanoes are always extinct
- Shape has nothing to do with eruption type
- Runny lava often builds broad shields

Answer key

For grown-ups. Fold this page away before handing over the rest.

Explosive · Explosive eruptions fragment rock or magma and throw ash and larger pieces into the air.
Effusive · An effusive eruption releases lava mainly as flows rather than a major blast.
False · Violent blasts describe explosive eruptions. Effusive eruptions mainly release lava flows.
Gas escapes more easily · Bubbles escape more easily through runny magma, which can reduce gas pressure and favor lava flows.
Trapped gas builds pressure · Sticky magma can hold bubbles in. If gas stays trapped, pressure can build and drive an explosion.
A steep cone volcano · The outline is tall with steep sides, matching a steep cone rather than a broad shield. Shape alone does not establish whether a volcano is extinct.
Thick and gas-rich; it can explode · Resistance to flow means the magma is thick. Many bubbles supply gas that can build pressure and drive an explosive eruption.
Runny lava often builds broad shields · Broad shields usually grow as runny lava spreads far from the vent. The shape does not prove that the volcano never had an explosive eruption.