A clear favourite as far as science in the kitchen goes. A classic, one that every kids must try at least once if not hundreds of time.
What you will need...
To make the salt dough:
Flour 2 cups
salt 2 cups
water 1 cup
The rest of the volcano:
A baking tray
A small drinking bottle
For the lava:
washing up liquid
Food colouring (red is a good choice)
vinegar (white is best)
Make your salt dough which is really easy. All you do is put the flour, salt and water in a mixing bowl and stir until you have a lovely not sticky ball of dough.
Put the drinking bottle on the baking tray and fill it half way with water, a generous amount of washing up liquid (fairy works really well) and 2-3 heaped teaspoons of baking powder.
Mix well and then use the salt dough to make a volcano shape around the bottle.
Now for the fun bit. Drop some vinegar into the solution in the bottle. Do it bit by bit until you get the effect you desire. When it starts fizzing you may need to stir it a little to start the reaction but you will find yourself a scene like this...