What you need to do your own underwater vulcanoe is (maybe not as good looking as the real Hawaiian below):
- A large container
- A glass / small vase / beaker, preferably with a small neck or collar for easier attachment of threads
- Yarn / string or steel wire
- Food Colour
Tie the cord / steel wire into the collar of the small container. In the large container you pour cold water. In the glass / vase / beaker you pour as hot water as you can (think of the risk of explosion with boiling water in glass!) And color the warm water with the food colour. Immerse the small beaker in the large container and see what happens!
The hot water is lighter than the cold water, and therefore wants up to the surface to lie there. It flows out of the smaller beaker to reach the top of the large container.