Model volcano big eruption, any good tips, i choose best answer *10 easy pts* please help?

ok, for our schools science fair my cl is making volcano things, and i want a really big eruption, but i cant use explosives or else i will fail the course, and vinegar and baking soda is too slow and small, mentos and soda is not what i want, i want an easy mixture that will make a giant eruption that still looks pretty real, so anything that is easy to get my hands on will work, i want it to be awesome, ANY IDEAS!!!