A Better Volcano

4/24/2020

We have all made volcanoes with baking soda and vinegar. But this volcano will teach you more about different things that come out of a volcano, and how they work together to build the volcano over time.

NOTE: This is best done outside - it is very messy!!!

What You Will Need:

A plastic or paper plate
A small bathroom cup - approximately 3 ounce size
Playdough
Baking soda
Vinegar
Molasses
Kitty litter
Optional - food coloring to make the lava red

Experimental Procedure:

Put the bathroom cup on top of the plate. Use the playdough to make a volcano shape around the cup. This represents the volcano when it has just started to form.
Put about a tablespoon of baking soda in the cup.
Put a small handful (about ¼ cup) of kitty litter around the outside of the cup. This represents one kind of lava that can be produced by the volcano. We will talk more about this in a minute.
Pour about ¼ cup of molasses around the cup, and let it run down the sides of your volcano and onto the bottom of the plate. This represents the other kind of lava.
Now, pour the vinegar into the cup and watch where the bubbles flow. After the mixture has stopped bubbling, notice the places where the bubbles popped in the kitty litter and molasses mixture. What kind of surface do you see? If you were an ant walking on that surface, would it be smooth and easy to walk on, or bumpy and hard?
Refill the cup with baking soda, add more molasses and kitty litter, and then erupt the volcano again. What do you notice about the base of the volcano? Is it the same width as when we started?

What’s Happening?

When a volcano erupts, it spews out lava. We all know this. But, not all lava is the same. Some lava has more gas dissolved in it than other lava does, and so it acts differently when it cools. Since these two different types of lava were first discovered in Hawai’i, they have Hawaiian names - aa (aah-aah) and pahoehoe (pah-hoy-hoy).

The kitty litter that you sprinkled around the volcano represents aa lava. If you look at the kitty litter closely, what do you see? You should notice that kitty litter is made up of little chunks of material that are kind of sharp and pointy. That is what aa lava is like, after it has cooled. It is sharp and pointy, and when you step on it, it sounds like glass breaking. Think of stepping on something sharp with your bare feet - you might say “Aah!”. That is one way to remember aa lava.

The other kind of lava is represented by the molasses. When you poured the molasses out of the jar or bottle, you probably had a stream of it running down onto the volcano. When you look at this stream more closely, you might notice that it is smooth and it flows easily. The other kind of lava that we are talking about, pahoehoe lava, acts more like molasses. It flows smoothly, and cools into smooth, wavy patterns.

When volcanoes erupt, sometimes the lava that comes out is aa, and sometimes it is pahoehoe. Sometimes, no lava at all comes out, and instead there will be ash, or even half-melted rocks! But, whatever comes out of the volcano, when it stops moving, it becomes part of the side of the volcano. Volcanoes actually grow every time they erupt! That is why your volcano is wider at the end of the activity than it was at the beginning.

Variations and Related Activities:

To actually see the buildup of gas pressure that leads to an eruption, put baking soda and vinegar in a zip-top bag, zip the top, and then put it on the ground and back up to watch it expand and pop.

Of course, it is also interesting to see how little baking soda it takes to make the volcano erupt, and if all the baking soda is used up in any one eruption.

Links to more information and activities:

Lava articles with photos of aa and pahoehoe lava:

More interesting volcano facts: