Cut the top off the soda bottle just below the screw top lid. This widens the top of the bottle slightly. Glue the base of the bottle to the center of the thick cardboard square. Measure the distance between the rim of the bottle and the middle of one of the edges of the cardboard. Cut the scrap cardboard into strips that are this length.
Fold both ends of the cardboard strips over by half an inch. This creates two distinct ends to each strip. Super glue one end of the strip to the top of the bottle and the other end to the cardboard square; continue until the strips encircle the bottle. Do not cover the aperture at the top of the bottle. You now have the framework for the mountain.
Tear the newspaper into rough strips. Pour five cups of PVA glue into a bowl and add one cup of water. Stir the mixture and soak one of the newspaper strips in it. Remove the newspaper from the mixture and lay it on the cardboard frame. Continue to do this until you have covered the frame and overlapped the newspaper into the aperture at the top of the bottle and onto the underside of the cardboard square. This gives the structure more strength. Do not block the aperture when you are doing this.
Continue building up the texture of the mountain by adding extra layers to the structure. As the structure gets thicker, pinch the newspaper to create the impression of rocks and other contusions on the mountainside. When the structure is dry, spray it with white primer and then paint it with the poster paint.
Mix equal parts vinegar and red food coloring in a jug and pour it into the aperture. Add baking soda to the aperture and stand back. This will demonstrate the flow of magma to the surface to become lava.