In this experiment, your group will create pressure in a bottle to reenact one of the special conditions under which a geyser erupts. A geyser is a hot spring that shoots a column of hot water into the air. Your group will make a model geyser using liquid soap, a bottle, and Alka-Seltzer® tablets.
Although geysers are rare, 60% of the geysers in the world are found in Yellowstone National Park, where one of the most famous is called Old Faithful. A geyser is a hot spring that erupts, shooting a column of water into the air. Geysers are rare because they require certain conditions—water, volcanic heat, and pressure. Water seeps underground and flows through channels of underground rock and then some of it collects in underground reservoirs. When the water inside a pocket of a closed-off reservoir becomes extremely hot, pressure begins to build. If there is enough pressure, the water will stay in liquid form until it is very hot (as opposed to changing to steam like boiling water). When the high pressure causes some of the water to finally change to steam, the steam will launch water out of the reservoir causing the geyser to erupt. When the geyser stops erupting, the pressure starts to build again in the reservoir pocket, and the whole process starts over.
Ask your group: “Do you know what a geyser is?” They likely know, but they may not know why one erupts and it also may be (depending on geography) that they have never seen one.
Tell your group that Old Faithful is a famous geyser located in Yellowstone National Park. Then ask: “How do you suppose the water can be spewed that high out of the ground?” Whether kids know the answer or not, this is a great set-up question before they do their own explosive experiment.
Now, break your group up into small groups, point them toward the student web page, and give each group a set of supplies—a copy of the Geyser Riser activity sheet, liquid soap, a bottle, Alka-Seltzer®, and a tub. They will need to fill their bottles with water and the bottles will overflow once they’ve followed the directions. You may need to arrange for each group to have a turn at the sink if you don’t have individual tubs.
After kids have done the experiment, ask: “What makes a bottle erupt?” The main point is simply that pressure needs to build up to create an eruption. Relate the bottle activity to geysers if that helps them understand.
Other ideas for follow-up activity questions include asking kids to predict what would happen if they didn’t cover the top of the bottle, or what would happen if more Alka-Seltzer® were added, or more soap. Kids should make predictions and then try it.
Do you know what a geyser is? It's a hot spring that erupts, shooting a column of water into the air. More than half of all geysers in the world can be found in Yellowstone National Park in the United States, where the most famous is called Old Faithful.