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🌋 Why do volcanoes erupt

Follow magma from its underground source through rising pressure, expanding gas bubbles, viscosity, eruption styles, ash, lava, and volcanic hazards.

4
lessons
~10 min
to learn
Adults
level
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What you’ll learn

  1. Where Magma Comes FromExplain how magma forms, rises, and collects in a connected volcanic plumbing system.Volcanoes begin with partial melting and buoyant magma, but an eruption requires pathways and enough pressure to overcome resistance underground.
  2. Pressure Turns Magma into an EruptionDescribe how falling pressure releases dissolved gas and how bubbles help drive magma toward the surface.Rising magma loses confining pressure, gas exsolves into expanding bubbles, and blocked or rapidly rising systems can become pressurized.
  3. Why Eruptions DifferConnect magma viscosity, gas content, ascent rate, and water interaction to effusive or explosive eruption styles.Runny magma often releases gas through lava and fountains, while sticky gas-rich magma can fragment into ash and explosive columns.
  4. What Eruptions Leave BehindDistinguish lava flows, ash, pyroclastic flows, lahars, and the landforms built by repeated eruptions.The eruption mechanism creates material and energy; gravity, wind, water, and landscape determine how hazards travel and how volcanoes grow.

Questions this course answers

Match each volcanic feature to its role.

A volcano connects underground magma storage to the surface through conduits and vents, although the underground system is often irregular rather than a simple pipe.

Why can rising magma become more explosive near the surface?

Deep pressure keeps volatiles dissolved. Near the surface, exsolution and bubble expansion add upward force and can shatter magma when gas cannot escape smoothly.

Put this pressure-and-gas sequence in order.

The sequence begins with rising magma and pressure loss. Gas exsolves and expands, then the magma releases energy through effusive or explosive eruption depending on its properties and pathways.

Grounded in trusted sources

  • U.S. Geological Survey, How Do Volcanoes Erupt? — https://www.usgs.gov/faqs/how-do-volcanoes-erupt
  • National Park Service, Volcanic Eruptions — https://home.nps.gov/subjects/volcanoes/volcanic-eruptions.htm
  • U.S. Geological Survey, Impacts & Mitigation: Eruption Styles — https://volcanoes.usgs.gov/volcanic_ash/eruption_styles.html
  • U.S. Geological Survey, Volcanic gases can be harmful to health, vegetation and infrastructure — https://www.usgs.gov/programs/VHP/volcanic-gases-can-be-harmful-health-vegetation-and-infrastructure
  • U.S. Geological Survey, Can earthquakes trigger volcanic eruptions? — https://www.usgs.gov/faqs/can-earthquakes-trigger-volcanic-eruptions
  • U.S. Geological Survey, About Volcanoes — https://www.usgs.gov/programs/VHP/about-volcanoes

Every Wunder lesson is built from real, reputable sources — never invented.

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