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5.25: Effusive Eruptions

Difficulty Level: Basic Created by: CK-12
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Isn't this an explosive eruption?

This is a strombolian eruption. This type of eruption was named for Mt. Stromboli in Italy. Strombolian eruptions spew lava into the air. But these eruptions do not have a massive explosion. They create lava flows.

Effusive Eruptions

Mafic magma creates gentler effusive eruptions. There is little or no gas. The lava is thin and fluid so that it flows over the ground like a river. Mafic magma pushes toward the surface through fissures. Eventually, the magma reaches the surface and erupts through a vent (Figure below). Effusive eruptions are common in Hawaii, where lavas are mafic.

In effusive eruptions, lava flows readily, producing rivers of molten rock.

Effusive Eruptions Damage

Effusive eruptions rarely kill anyone because they move slowly. People can usually be evacuated before an effusive eruption. Still, effusive eruptions can be destructive. There is not much anyone can do to stop a lava flow from destroying a building or road (Figure below).

A road is overrun by an eruption at Kilauea volcano in Hawaii.


  • effusive eruption: A relatively gentle, non-explosive volcanic eruption.


  • Mafic magma creates effusive eruptions. The pressure builds but the lava flows fairly quietly.
  • Effusive eruptions cause damage but rarely kill anyone.
  • Mafic magma cools into different types of flows like a'a, pāhoehoe, and pillow lava.


Use these resources to answer the questions that follow.

Understanding Volcanoes: Kilauea-A Volcano Lab at http://dsc.discovery.com/tv-shows/discovery-presents/videos/understanding-volcanoes-kilauea-a-volcano-lab.htm (3:01)

  1. How long has Kilauea been erupting?
  2. What are the lava flows building?
  3. What is this land called?
  4. Why do scientists map the tephra?
  5. What are skylights? What do scientists learn from them?


  1. Why do mafic lavas flow rather than explode?
  2. Compare and contrast lavas from explosive and effusive eruptions.
  3. Why do effusive eruptions sometimes cause a lot of damage?


effusive eruption

effusive eruption

Relatively gentle, non-explosive volcanic eruption.

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Difficulty Level:
6 , 7
Date Created:
Jan 04, 2013
Last Modified:
May 11, 2016
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