You'll probably ask what did we create for our science fair.
We made a volcano... but, why did we do a simple volcano? It's easy, well... volcanos are not a simple thing, I mean, they are not just a rupture in the surface which allows hot lava and volcanic ashes.
Generally, they're formed at the boundaries of the tecntonic plates, inside has open fires where the lava rises from the magma chamber, a reservoir where lava accumulates.
So, what we did for our science fair was a little volcano which would represent a real volcano eruption so people could understand better the process it requires.

Step 1: Volcanoes!

First we have to know what is a volcano.
A volcano is an opening, or rupture, in a planet's surface which allows hot, molten rock, ash, and gases to escape from below the surface. Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time.
Volcanoes are generally found where tectonic plates are diverging. Volcanoes can also form where there is stretching and thinning of the Earth's crust.

Step 2: How Volcanoes Work?

Volcanic activity ranges from emission of gases, lava emissions to extremely violent explosive bursts that may last many hours. The types of eruptions determine the relative volumes and types of volcaniclastic material and lava flows, consequently the shapes and sizes of volcanoes.

A volcanic event occurs when there is a sudden or continuing release of energy caused by near-surface or surface magma movement. The energy can be in the form of earthquakes, gas-emission at the surface, release of heat, which is geothermal activity, explosive release of gases (including steam with the interaction of magma and surface of ground water), and the non-explosive extrusion or intrusion of magma.
An event could be non-destructive without release of solids or magmatic liquid, or if there is anything to destroy, could be destructive with voluminous lava flows or explosive activity. Destruction usually refers to the works of mankind (buildings, roads, agricultural land, etc.).

Step 3: Now We're Ready!

Now that we know almost everything about the volcanoes, we can do our little volcano without problems!

Materials we need:
Volcano:
Container
Glue
Toilet Paper
Clay (If you prefer to do it without glue and toilet paper).

Lava:
Baking soda
red coloring
vinegar.

Step 4: The Base

The first thing you have to do is:
Lay down a piece of carton and put a container at the center. In the container we will mix the "lava" and it will be the base of your volcano. You can mold clay from the base to the top of the can. In our case, our little volcano was made of a mix of liquid glue and water and soft paper like toilet paper or kleenex.
When you do your volcano try to make it look lumpy instead of smooth, since real volcanoes don’t look like perfect cones most of the times.

Step 5: A Cool Volcano

When you finished doing the step one, you obviously have to leave it for a couple of hours until it dries. When it dries you can decorate your volcano with all the colors you want to. We were considering to paint it green, since volcanoes also exist in other planets. Actually the biggest volcano of all the Solar System is located in Mars, but in our science fair they wouldn't let us present a green volcano from another unknown planet!
Anyways the best color you can paint it could be a mix of brown tones almost like red and paint some parts with grey.

Step 6: The Lava

Color some vinegar with red food coloring, so it would seem like real lava. You can mix in a tablespoon of dish soap.
When the mix looks already like "lava" pour the mixture into the container in the middle of your volcano.
In this step, you can asimilate in how does the volcano has the lava in their interior and it goes getting hotter and hotter until it risesand comes out in the crater.

Step 7: Come Out Lava!

Your volcano is ready to make the biggest eruption ever. (Imagine)
Take baking powder and pour it on a square of toilet paper. Fold up the toilet paper/paper towel. Keep it closed with rubber bands. Drop the baking soda roll in the vinegar.
Step away! Once your paper disolves your volcano will explote!