Tony Pirkl, age 12, of Wi.ndom, Minn., for his question:
HOW DOES A GEYSER ERUPT?
Old Faithful is the name of a famous geyser in Wyoming's Yellowstone National Park. Once every 65 minute sit erupts for about four minutes. Water is shot between 120and 150 feet into the air. People have been keeping records on old Faithful for more than 80 years, and in that time it has never missed an eruption.
A geyser is a spring that shoots hot water into theair with explosive force. Some geysers toss steam and hot water into space on a regular schedule, but most erupt at irregular intervals with no one being sure just when the show will go on.
Yellowstone National Park has at least 200 active geysers. In some, boiling water only bubbles above the ground. In others, water soars over 100 feet into the air.
Geysers are formed near rivers and lakes where water drains through the earth deep below the surface. A deep channel will reach from the surface to a spot far into the earth. Then cold water seeps down this channel until it reaches rocks that are very hot.
To have a geyser, you must have a location with hot rocks deep below the surface of the earth, plus a seepage of water.
When water is standing in a deep channel, the hot rocks heat the water that is far below the surface. Even though the water reaches a boiling point, it cannot boil because of the weight of the column of cold water above it. Gradually, however, the heat at the bottom will produce steam. The rising bubbles lift the water column a little, pushing some of the water in the channel over the opening onto the earth. This makes the column of water a bit lighter, and more water is able to turn into steam. This in turn lifts the column still more until suddenly all the water near the bottom expands into steam and forces out the rest of the water above it in a steam explosion. This explosion is the spouting of the geyser.
As the water and steam settle, some of the water seeps back into the crevices that feed the channel. When the channel is full, the buildup of steam starts again.
Geysers have been compared to volcanoes. They do indeed act similarly, with the volcanoes shooting melted rock into space while the geysers erupt with water.
Some geysers erupt water that contains dissolved mineral matter. After the water hits the earth, deposits of silica or lime carbonate often are left. Around many geysers are deposits which have been shaped into curious and beautiful forms. A geyser of this type is the Giantess, which is found in Yellowstone Park. Here the mineral deposits have formed a large crater which is filled with sparklingly clear water between eruptions.