Start with all your old playdough!  Mix it together for that great swirly look!  (Or make a batch click here for recipe.)
You will also need a big ole piece of sidewalk chalk.
Place a handful of playdough on a plastic plate.
Push the chalk into the playdough to create a volcano shape.  Squish the sides into a nice volcano shape.  Leave that chalk there and let the playdough dry.  (Remove the chalk after a few hours so it will dry inside as well!)
 Once the volcano is dry (may take a few days!), you are ready to put a heaping tablespoon of baking soda into the center of that volcano.
 I prepare a cup of vinegar that I have colored with red food dye for each child.
We “explode” our volcanoes outside!  So much fun!  A kindergarten favorite!