Geyser, << GY zuhr, >> is a spring that throws up hot water with explosive force from time to time. Often, the water shoots up in great columns, cloudy with steam.
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“Old Faithful” in Yellowstone National Park is probably the world’s most famous geyser. In most years, it erupts, on average, about every 90 minutes. The actual intervals between eruptions vary from about 51 to 120 minutes. Most eruptions are 120 to 150 feet (37 to 46 meters) high. “Old Faithful” has not missed an eruption in over 80 years.
Most other geysers erupt at irregular intervals. No one knows when they will go off. Some geysers erupt several times an hour. Other geysers do not go off for days, weeks, or even months. In some, the water only bubbles above the ground. In others, water soars more than 100 feet (30 meters) high.
Where geysers are found.
There are at least 300 active geysers in Yellowstone Park. Another group of geysers lies 70 miles (110 kilometers) from Reykjavik, Iceland. The geysers erupt in the midst of barren lava fields. A circle 10 miles (16 kilometers) in diameter holds dozens of geysers. Still another group of geysers is far to the south in New Zealand.
How geysers form.
Geysers form where water drains through the ground deep below the surface. A channel reaches from the surface far underground. Cold water seeps down this channel until it reaches rocks that are hot. Then it fills the channel. The water at the bottom is heated by the rocks. But the water 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. Steam begins to form. The rising bubbles lift the water column a little, pushing some of the water onto the surface. That makes the column of water lighter. More water turns into steam. This process, in turn, lifts the column still more. Suddenly, all the water near the bottom of the channel expands into steam and forces out the rest in a steam explosion. After the water and steam settle back, some of the water seeps back into the earth and fills the channel again. The crevices that feed the channel usually contain constrictions or sharp bends. These features prevent the water from mixing to a uniform temperature. Such mixing would keep the water from becoming superheated enough to explode into steam.
Geysers have often been compared with volcanoes, which act similarly. But volcanoes shoot melted rock. Geysers erupt water containing dissolved mineral matter. After the eruption, the water evaporates or seeps back into the earth. It leaves deposits of silica or lime carbonate. These deposits may form castlelike figures, towers, or other curious shapes. Many of them form cones. Some, such as the “Giantess” in Yellowstone Park, form craters that fill with clear water between eruptions. Little water is left after the eruption of a geyser that has a cone. One exception is the tiny “Model” in Yellowstone Park. All the water from this geyser falls back into its cuplike cone
