How to Make an Erupting Water Bottle Volcano
This volcano can be made from anything, from sand, paper mache, clay, foam, really anything that you can find to use. The Basics are you need a tube (or bottle of course), vinegar, baking soda. You can build up around the bottle with many above mentioned items to make it more realistic, the choice is yours.
One way to achieve your volcano look is to take a few pieces of cardboard around a soda bottle. You can leave that be or add a wrap around with paper mache, let dry and paint it the next day.
The eruption is done easily by one of two methods. You could packed the tube or bottle of the volcano with baking soda, then add vinegar quickly into the tube or bottle. To add a touch of molten lava look, add a few drop of red food coloring to the vinegar. This method will produce a slow drizzle that last longer with more baking soda.
To get a hard eruption that will probably make a huge mess, so may be better done outside, you could use the Diet Coke and white Mentos route. Once again pretty basic, use a Diet Coke bottle, pour out a few inches and tape about 3-4 white Mentos together and drop in. This is a quick reaction, so moving away quickly is highly recommended.
So to recap, all you need is these few items listed, creativity and a little time.
Tube or Bottle
Baking Soda and Vinegar (or)
Diet Coke and Mentos
Red Food Coloring or dye (optional)