Ricky Bergquisti age 10, of Seattle, Washington, for his questions:

What makes old Faithful erupt ?

Old Faithful, of course, is a geyser among lots of other geysers in Yellowstone National Park, Regularly every hour or so, it faithfully erupts about 1,000 gallons of steamy water some 120 feet into the air, Like all geysers, the roots of Old Faithful go dawn into beds of hot lava below cooler layers of surface rocks. This lava was probably smothered before it had a chance to cool millions of years ago,

Deep below ground, a web of cracks and crevices run water into a central hole, or vent. These are the roots which feed Old Faithful and keep it erupting.  A boiling kettle can gently turn one quart of water into 1600 quarts of steam. Old Faithful comes up in one big spurt because quantities of its water is turned to steam in a flash. At sea level, where the pressure is 14.7 pounds per square inch, water boils at 100 degrees Centigrade. When the pressure above is doubled, or equal to the weight of two of our atmospheres water does not boil into steam until it reaches 120 degrees Centigrade. Under pressures of 147 pounds per square inch, or ten atmospheres, water refuses to boil into steam at less then 180 degrees Centigrade.

Now the roots of Old Faithful are fed by ground water, some running through cooler pockets above and some flowing into the seething lava beds below. The hot lava soon heats its water to 100 degrees Centigrade, but this water is under pressure from rocks and cooler water above. It just refuses to boil and continues to heat,

Temperatures from below continue to rise until the superheated water has boiled some of the water above it, heated  water, being under less pressure, it boils up into steam. It does so and spills a little over the rim of the geyser,

This small outburst immediately releases the pressure on the superheated water trapped below. Under less pressure it suddenly becomes steam In a flash, it pushes up through the vent reaching for more space. It pushes and drags up all the warm and hot water in its path and Old Faithful erupts into the air.

Below ground, more water is already filling in the roots of the great geyser to heat up and erupt all over again.