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My brother-in-law and his family went on an epic month-long vacation this summer along the Pacific Northwest and over to Wyoming. One of my favorite videos they sent was of their family watching the famous Old Faithful geyser in Yellowstone National Park.

It was simply spectacular, even just seeing it in photos. Nature never fails to amaze me with its power and beauty.

We are in the middle of summer break, and to be honest, there are a lot of boring days around here (we didn’t take the epic trip to see Old Faithful, but it’s definitely on my future summer dream vacation list).

I wanted to liven up our July with a few science experiments. And what better way to liven things up than with a geyser eruption at home?

Today I’m so excited to share with you how to do a soda geyser with your kids. And don’t throw the soda bottles away when you’re done with them, because we’ll use them in my next STEAM for Kids experiment where I’ll teach you how to make tornados in a bottle.

So, not only are we teaching our kids about STEAM, we are also teaching them how to be economically and environmentally responsible by reusing materials. 😉

Also, if you are like me and worried about your kids and yard getting all sticky from the soda – I have a great solution for that too! Keep reading to learn all about this fun summer activity!

First Let’s Talk About the Science

A geyser is a geological phenomenon in which a hot spring is under pressure and sends a column of boiling water and steam into the air. Geysers are extremely rare and only occur where 4 unusual conditions are met:

  1. Hot rocks below
  2. An ample groundwater source
  3. A subsurface water reservoir
  4. Fissures to deliver water to the surface

Old Faithful is the world’s most famous geyser. Located in Yellowstone National Park in Wyoming, United States, Old Faithful get’s its name from its predictable eruptions that happen around 20 times per day.

Old Faithful erupts every 60 to 110 minutes. The eruptions can last from around 1.5 to 5 minutes. The eruptions are predicted with a 90% confidence rate within a 10 minute variation based the height and duration of the previous eruption.

In fact, there is a lot of math that goes into geyser predictions. The prediction is mainly based on analyzing the statistics that have been faithfully recorded for over 100 years.

Old faithful can shoot up to 180 ft high, and expel up to 8,400 gallons of boiling (up to 204 deg F) water.

You can read more about Old Faithful on Yellowstone Park’s webpage.

A soda geyser is created by a physical reaction between carbonated soda and the mint that causes the liquid to erupt out of the bottle similar to how a geyser erupts out of the ground.

The carbonated beverages contain Carbon Dioxide (CO2). When you shake a bottle of soda before opening it, the air at the top of the bottle creates large bubbles in the liquid. These large bubbles help the CO2 escape the liquid more easily, causing a little eruption.

In this experiment we’re taking the shaken soda eruption up a notch by adding mentos instead of air bubbles. The mentos surface has lots of tiny pits. The rough surface creates nucleation sites where more CO2 bubbles can form.

Since the mint is heavy it drops to the bottom of the bottle creating lots of CO2 bubbles on the way down. The rapid nucleation of CO2 bubbles from the liquid solution results in the eruption we see in this experiment. (source Wikipedia)

Not surprisingly (after learning about geysers above), the soda geyser works best when the soda is warm. So be sure to leave your soda bottle out at room temperature, and maybe even out in the sun for the afternoon before using it for this experiment.

Soda Geyser Experiment

This is a messy, but fun experiment to try with your kids. This experiment is fun for kids aged 1+. For kids age 1 to 3 you will need to demonstrate the experiment while your children learn and observe. Let kids aged 3+ help you, and kids aged 5+ can try to do the experiment themselves!

Me and my 5 year old son


We are creating an eruption of soda. So, be prepared for yourself and your children to potentially get soaked in minty Diet Coke. Wear clothes that are ok to get wet (such as swim or athletic wear).

Eye protection may be helpful if you think you or your children won’t move away quick enough and they have sensitive eyes.

Also, since you will be doing this experiment outdoors, remember to wear appropriate sun protection, and also properly clean up the soda with water to prevent ants and other bugs from swarming to the reaction site.

Materials Needed:

  • Diet Coke bottle (any size – we tried 2L, 1L and 24oz)
  • Mentos
  • Paper
  • Plastic card (like credit card, gift card, etc)
  • Geyser tube (optional)
  • Towels (optional, but recommended)
  • Sprinkler (optional, but recommended)


  1. Remove the bottle cap and set the full bottle of soda on flat ground (or a table) outside in an open location

2. Roll the paper up to a cylinder shape (it should be the same diameter to your bottle opening)

Make sure the bottom opening is the same size or slightly smaller than the bottle opening

3. Place the plastic card in between the bottle opening and the paper cylinder

Align the plastic card between the bottle opening and the paper cylinder

Note: alternatively instead of steps 2&3, you can use a geyser tube (which is much easier!)

4. Have your child count out 7 Mentos and place them into the cylinder

1, 2, 3, 4, 5, 6, 7!
This is good hand-eye coordination/fine motor skills practice for the younger kids!

5. Quickly pull the plastic card out, allowing all the mentos to fall into the soda bottle and RUN!

Our 2L bottle geyser, using 7 Mentos

Repeat varying number of mentos, size of bottle, and/or type of soda and record or discuss how this changes your results (see more ideas in the What Happened section below)

Our 1L bottle geyser, using 7 Mentos

Once you’re all done experimenting, turn on the sprinklers. This will help wash away the sugary soda from your yard and body. My kids love any reason to run through in the sprinklers on a hot summer day. 🙂

Soda geysers followed by running through sprinklers = perfect summer day for us!

What Happened:

According to Steve Spangler, one of the first science presenters to do this experiment on YouTube, the optimum combination to achieve the largest soda geyser is 7 Mentos in a warm (75-85 deg F) Diet Coke. I believe in experimenting to prove this yourself.

Try experimenting by testing Coke, Diet Coke and Sprite, all with same number of Mentos and temperature, what difference does type of soda make? Vary the number of Mentos: use 4, 7, and 10 in the same type of soda the same temperature. What difference does number of Mentos make for the geyser height? Try varying the temperature of the soda: use one refrigerated bottle, one at room temperature, and one that had been warmed in the sun, all in the same type of soda with same number of Mentos. How does temperature affect the geyser height?

There are so many different variations that can be done on this one experiment that make it fun for kids and adults of all ages.

Steve Spangler also invented a geyser tube that allows you to do this experiment a little easier than the rolled paper and plastic card method I used. Here is the Amazon link to the Geyser Tube attachment if you’d like easier, more consistent results.

So what are you waiting for?! Go try this fun summer experiment with your kids right now!

Have you done this experiment before? How did it turn out? What do you think of my sprinkler idea – great idea or crazy? 🙂


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