Simple Eruptions

The simplest and safest way to model an eruption is to mix vinegar, baking soda and a few drops of dish soap. We made two modifications. We added red food coloring to the vinegar to give the fluid more lava-like appearance. We also added alka seltzer (crushed and mixed in with the baking soda). The alka seltzer probably wasn't worth the trouble/cost but, as the red mixture bubbled away down in the vial, our thoughts did drift to the lava ponds we have seen.