What it shows
A composite volcano is built from alternating layers of hardened lava and ash. Magma rises from a chamber deep below through a central pipe and sometimes side vents, and the cut-away shows how the inside connects to the crater at the top.
The science
Molten rock, called magma, is less dense than the solid rock around it, so it rises and collects in a chamber a few kilometres down. Pressure from gases dissolved in the magma pushes it up the central vent. Each eruption lays down a layer of lava or ash, and over thousands of years the layers stack into a steep cone. Cutting the model in half shows the layers, the chamber, the vent and the crater in one view.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A thermocol or cardboard base
- Newspaper and flour-and-water paste, or clay
- Red, orange, grey and brown paint
- A straw or pipe for the central vent
- Labels on toothpicks
Safety
For this project: An adult should cut thermocol with a blade. Flour paste should be used fresh and dried well so it does not grow mould.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Draw a semicircle on the base for the half of the mountain you will build and mark the vent in the middle.
Fix the straw upright at the vent position; it will become the central pipe.
Build the cone around it with crumpled newspaper and paste or clay, leaving the flat cut face open.
On the cut face press in alternate bands of grey and brown clay to show ash and lava layers.
Shape a bulge of red clay at the bottom of the vent for the magma chamber and a branch for a side vent.
Paint the outside brown and green and the chamber and vent bright red and orange.
Add labels: crater, central vent, side vent, lava layer, ash layer, magma chamber.
Write a small card explaining why composite volcanoes are steep and why they erupt violently.
What you should see
A half-volcano that a viewer can read from bottom to top, with every labelled part in the right place and the layers visibly alternating.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is the difference between magma and lava?
Magma is molten rock underground; lava is the same rock once it reaches the surface.
2Why does magma rise?
It is less dense than the solid rock around it, and dissolved gases push it up.
3Why are composite volcanoes steep?
Their lava is thick and does not flow far, so it builds up near the vent.
4Name a volcano in India.
Barren Island in the Andaman Islands is the only active one.
Take it further
Build a second, low and wide shield volcano beside it and compare the two shapes.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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