hcho15.html

Warm soda cans fizz like crazy.	But nothing blows up like a geyser.

Below ground, hot rock boils water into steam.	The steam builds up, but not much seeps out. (Note the tiny opening at the top.)	Then POW! The geyser "blows its lid."

Home Crew, want to make your own geyser explode? Full steam ahead!


	Water
	Liquid soap
	Small bottle a narrow neck
	Alka-Seltzer tablets (broken into pieces)
	Large tub or sink
	Sponge for clean-up

*	Note: The gas in a geyser is super hot steam that could burn you. Instead of heat, the Geyser Riser you're making uses a chemical reaction to make a safer gas.
	Fill a bottle almost to the top with very warm tap water. Add a few drops of liquid soap.
	Set the bottle in a large tub or sink to catch the spills.
	Drop a broken Alka-Seltzer tablet into the bottle. Immediately put your palm firmly over the top.
*Do you feel the pressure?* *Does it increase or decrease?* *What do you hear?*
	Lift your hand and listen again.
*Do you hear a "pop" sound as the gas rushes out?* *What makes the soap jet out like that?*
	If you repeat the experiment, try adding more soap and another Alka-Seltzer tablet.
*Is the pressure different?* *What about the "pop"?* *Does the soap jet out the same way?*

Gas expands, especially when it's hot. Squeeze a balloon that's half full. It seems to push back, but it's really the air inside pushing out against the balloon walls. Now squeeze a full balloon. It really pushes back, huh? Like a balloon, geysers fill with gas, but the walls don't stretch. So the pressure (pushing) inside gets harder and harder until, whoosh! The gas shoots out a hole, taking underground water with it. Some geysers shoot water up to 400 feet in the air! And some erupt all the time. Old Faithful, a famous geyser in Yellowstone Park, erupts on an average of every 75 minutes.