Paul Johnstone, age 10, of Quincy, I11., for his question:

HOW ARE GEYSERS FORMED?

Geysers are springs that throw up hot water with explosive force from time to time. They are formed near rivers and lakes where water drains through the earth deep below the surface.

As part of a geyser, a deep channel reaches from the surface far into the earth. Cold water seeps down this channel until it reaches rocks that are very hot. Then it fills the channel and the water at the bottom is heated by the rocks.

But the water in the channel cannot boil because of the weight of the column of water above it. Gradually, the heat at the bottom of the column rises far above the boiling point for water, and steam begins to farm.

As steam forms, the rising bubbles lift the column a little, pushing some of the water in the channel over the opening onto the surface of the earth. That makes the column of water lighter and more water is able to turn into steam.

This building up of steam in turn lifts the column still more, until suddenly all the water near the bottom of the channel expands into steam and forces out the rest of the water in a great steam explosion.

After the water and steam settle back on the earth, some of the back into the earth and fills up the Channel again