How Volcanoes Erupt
Lesson notes
Overview
Magma rich in dissolved gas rises, bubbles expand and pressure drives an eruption. This topic is rated beginner and is number 7 of 98 in Earth & Space. Core ideas and first intuitions. No prior knowledge needed.
What you are seeing
The panel above shows the steps of a process, laid out in order. Click a step to see what happens next. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
Magma rises because it is less dense than the surrounding rock. As it nears the surface the pressure falls, and dissolved gases such as water vapour and carbon dioxide form bubbles that expand violently. Runny basaltic magma lets gas escape, giving gentle lava flows, as in Hawaii, whereas thick silica-rich magma traps gas until the pressure causes an explosive eruption, throwing ash and pyroclastic flows, as at Mount St Helens.
Reading the relationship
The expression "pressure release" is a compact summary of the idea. It uses the symbols p, r, e, s, u, l; name what each one stands for before you start. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Start by only moving one slider at a time. Say aloud what you expect, then check.
Common pitfalls
Earth and space systems work on very different scales of time and distance. Check which scale a number refers to before comparing it with another.
How it connects
It builds on “Earthquakes and Seismic Waves”, the topic before it in Earth & Space. Once you are comfortable, continue with “Tsunami Speed”.
Why it matters
Earth and space science helps us understand our planet, its climate and the wider universe.
Where you might use it
- Revising “How Volcanoes Erupt” before a class, exam or certification
- Forecasting weather and understanding climate records and their uncertainty
- Planning for earthquakes, floods and other natural hazards in cities
- Interpreting satellite images, space missions and the age of rocks and stars
Frequently asked questions
What is How Volcanoes Erupt?
Magma rich in dissolved gas rises, bubbles expand and pressure drives an eruption. It is a beginner topic in Earth & Space.
How do I use the How Volcanoes Erupt simulation?
The panel at the top shows the steps of a process, laid out in order. Click a step to see what happens next. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression pressure release packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Core ideas and first intuitions. No prior knowledge needed. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “Earthquakes and Seismic Waves”, the previous topic in Earth & Space. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.