Pour 1 tbsp. of baking soda into a 1.5 oz. clear glass bottle with flat sides, such as an extract bottle.
Cover the top 3 inches of the bottle with a thin layer of gray modeling clay.
Use a plastic drinking straw to scrape a thin path through the clay down the center of both flat sides of the bottle so you can see the glass. This will represent the conduit for the lava. Scraping both sides allows light to show through.
Place the bottle in the center of the pie plate and add a layer of brown clay on each side of the bottle without covering the flat sides of the glass. The brown clay represents the Earth's crust. The clear glass opening at the bottom represents the magma chamber. You may color it red with a marker washable marker, if desired.
Add gray clay to the sides of the bottle over the brown clay to represent the side of the volcano.
Mix a drop of food coloring into 2 tbsp.. of vinegar.
Pour the vinegar into the bottle to make the volcano erupt.