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Deep underground some rock melts into magma. Magma is lighter than the solid rock around it, so it rises and collects in magma chambers. Some of it pushes up through cracks and vents; once it erupts it is called lava.

Magma contains dissolved gas. In thin, runny magma the gas escapes easily and lava flows out of the volcano, as at Hawaii's volcanoes. In thick, sticky magma the gas cannot escape, pressure builds up and the gas bursts out violently, as at Mount St. Helens in the USA.

Kīlauea's lava in Hawaii erupts at about 1,170 °C. You can estimate lava's temperature from its glow: yellow is about 1,000–1,200 °C, orange 800–1,000 °C and red 600–800 °C.

Experiment: Lava race: runny or sticky?

1. Put a tape start line near the top of the tray and a finish line 20 cm lower.
2. Plan a fair test: what will you keep the same? (Same amount of liquid, same slope, same start line.)
3. Predict which 'lava' will be fastest and which slowest.
4. Pour one teaspoon of the first liquid on the start line and time how long it takes to reach the finish line. Stop at 3 minutes if it has not arrived.
5. Repeat for each liquid, then do the whole race a second time.
6. Order the liquids from runniest to stickiest. Which would be like Hawaii's lava, and which like the magma of an explosive volcano?

Liquid	Prediction (fast / slow)	Time, try 1 (s)	Time, try 2 (s)
Water
Cooking oil
Golden syrup / honey
Ketchup

Questions

1. Draw and label a shield volcano and a composite volcano. How are their shapes different?

   🍎

2. Which liquid was the stickiest 'lava' in your race? How did you keep the test fair?

3. Explain why sticky magma can cause an explosive eruption.

4. Lava glows red. Is it hotter or cooler than yellow lava?

   hotter / cooler

Sources for every fact on this sheet: echoesof.science/school/volcanoes/sources/

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