Eruption Types & Volcano Shape

Activities to try

1. 1

   Eruption workshop: dial the magma, watch style and shape change

   Why it works: Eruption style and volcano shape are both consequences of two magma properties — thickness and gas content — not separate or random categories; a volcano's shape is evidence of how it erupts.

   1. Set two controls: how THICK the magma is (runny → sticky) and how much GAS it holds (low → high).
   2. Before running, PREDICT what will happen: gentle ooze or violent ash blast? Flat volcano or steep one?
   3. Run the eruption and watch the outcome on a spectrum from oozing lava flow to explosive ash column.
   4. Repeat eruptions and watch the volcano's profile build up over time into either a broad low shield or a steep composite cone.
   5. Try the opposite extreme (e.g. thin+low-gas, then thick+high-gas) and compare how the SAME setup becomes a very different volcano just by changing the magma.
2. 2

   Paired cross-sections: read why one is steep and one is flat

   Why it works: The mapping property → eruption style → shape can be read off a volcano's cross-section; shape is built up by the kind of eruptions, not decorative.

   1. Study two labelled volcano cross-sections side by side: a broad shield and a steep layered composite cone.
   2. Reveal, for each, the magma properties (runny + low-gas vs sticky + gas-rich), the eruption style, and a real example.
   3. Answer the lift-the-flap question 'Why is this one steep and that one flat?' and check against the revealed cause.
   4. Describe in your own words how runny lava spreads to make a wide shield while sticky lava and ash pile near the vent to make a steep cone.
3. 3

   Thin vs thick 'magma': a hands-on fizz investigation

   Why it works: Thick magma traps gas so pressure builds and releases suddenly (explosive), while thin magma lets gas escape gently (effusive) — the violence comes from trapped gas, not the amount of liquid.

   1. Set up two clear bottles: one of water, one of thick syrup or honey, each with a little bicarbonate of soda.
   2. Before adding vinegar, PREDICT which will 'erupt' more violently when gas forms — and say WHY.
   3. Add the same amount of vinegar to each (over a tray, bottles left open) and record what you actually see. Look for whether bubbles escape quickly from the runny water, and whether the thick syrup holds bubbles in a rising foam that pushes up and out. Results can vary: in thick syrup the vinegar mixes in slowly, so it may fizz less. Write down what happened rather than what you expected.
   4. Compare a fizzy drink opened gently with one that has been shaken (adult-supervised, over a tray). Both are the same thin liquid, so this is not a thick-vs-thin test. It shows how gas dissolved under pressure can rush out suddenly when the pressure is released, like gas coming out of rising magma.
   5. Using what you observed, say which bottle is the better model of effusive (runny) magma and which of explosive (thick) magma. Explain why, and name one way the bottles are not like real magma.