John Hixon, age 10, of Montgomery, Ala., for his question:
WHY DON'T GEYSERS EVER RUN OUT OF WATER?
Every hour or so, Old Faithful spouts up his foamy fountain 120 170 feet into the air. Each display uses about 10,000 gallons of steamy water, at 200 degrees Fahrenheit. This has been going on for more than 100 years, and one would expect the old geyser to run out of water supplies.
Old Faithful and the other geysers of Yellowstone National Park were discovered in the 1870s. They erupt their steamy fountains summer and winter, even when the frosty ground is covered with snow. So far, they show little or no signs of running out of water. In Iceland, everybody knows that their geysers have been spouting for many, many centuries.
The secret of a geyser's never ending water supply is filling and refilling. Suppose you fill a kettle, wait for it to boil, pour the steamy water out and fill it up again—again and again. This is somewhat like the way in which a geyser works. However, the kettle, the water and the furnace are much bigger and are buried deep underground.
Where there is one geyser there are sure to be many more. This is because they form in regions where volcanoes once erupted their seething hot lavas. A lot of this volcanic heat was trapped down below, where the rocks are still hot very hot. This explains the furnace that heats the steamy geyser water.
The water itself comes from rains and melting snows. A lot of this rainfall sinks down into the earth's rocky crust. It becomes buried ground water. Some of it seeps and trickles into rocky caves and pockets down there below the surface.
Some of these buried pockets are very, very hot. As ground water trickles into them, it boils and becomes steamy foam. Suddenly, it boils up and erupts in a frothy plume. This empties the geyser's buried kettle. But it is not the end of its water supply. Meantime the rain falls and the snows melt and more water seeps down into the ground. There is always plenty of ground water to refill the empty kettle and the process goes on and on.
A geyser may keep spurting for hundreds and perhaps thousands of years. Even then, it does not fail because it runs out of ground water. In time, the rocks below gradually lose their heat. When they finally cool down the geyser stops erupting because there is no more heat to boil the water.