Beulah Byrdstraw, age 13 of Gary, Ind., for her question:

How is Old Faithful timed?

Old Faithful has been a glamor boy since the 18701s. At that time his picture was used to convince Congress that his vast scenic home should be set aside as Yellowstone National Park ‑ the first and still the largest of our National Parks. Millions of people have traveled countless miles to see the famous geyser spout up his plume of steam and water and the old trouper never misses a performance.

We expect a little temperament from a star performer and Old Faithful is no exception. His white fountain varies from 120 to 170 feet in height. What's more, his shows are not as regular as clockwork, He may erupt after 38 minutes and he has been known to keep his audience waiting 81 minutes between shows, On the averages his dazzling show occurs every 65 minutes.

Between shows, you can see the stage on which he performs. It is a cone or dome of rock, formed from minerals dissolved in the boiling water. Center stage is the hole through which the glamorous geyser makes his entrance. The hole leads deep down into the earth's crust.

The whole region of Yellowstone happens to be very interesting just below the surface of the ground. Afew million years ago this area was a mass of seething lava. The surface nearest the; air cooled and became solid, This layer of cool, solid rock formed a cap over the hot lava below, holding its heat in like a pressure cooker,

Old Faithful's roots are a series of cracks, vents and, maybe$ small caves into these hot buried. rocks. Ground water seeps down into these roots and heats up like water in a kettle. Some of the water becomes superheated steam and steam, being; a gas, needs more room than liquid water. It can be compressed only so long, then it breaks out of its prison. The steam and boiling water erupt through the central vent of the geyser and Old. Faithful is once again on stage.

There are some 3,000 geysers in Yellowstone. Some erupt at fairly regular intervals and some spout when they feel like it. Giant Geyser's fountain is almost twice as high as Old Faithful's, but the Giant erupts but once every week or two. Then his display lasts about an hour,

A geyser's eruptions depend upon the underground factors which cause it. Old. Faithful must get a regular supply of ground water. His roots the kettle in which he boils this water, must have remained the same size and shape through the ages. He can erupt pretty much on time because he has exact tools with which to work. The underground. kettle fills with much the same amount of water each time. The hot kettle boils the water and turns some to steam. The geyser erupts and the kettle starts to fill up and boil all over again.