Yellowstone National Park - The Queen of Geysers

Old Faithful, the symbol of Yellowstone Park, is an impresario: its eruptions are pure showmanship. Each begins, as though to gather an audience, with a few spurts and splashes that go on intermittently for as long as half an hour. Occasionally a series of splashes seems to be reaching for a crescendo, and a spurt shoots 10, 20, even 30 feet into the air; but such tantalizing displays are mere overtures to the main show. The eruption, when it finally happens, gives little warning. A splash simply swells into a column of water that rises higher and higher, becoming a great steaming fountain well over 100 feet high, sometimes nearly 200.

The spectacle is awesome. During the 1½ to 5 minutes that the geyser "plays," hurling as much as 8,400 gallons of water high into the air, it is a thing of tremendous power. It is also a thing of great beauty, graceful, symmetrical, and never entirely predictable.

Contrary to popular opinion, Old Faithful does not go off every hour on the hour, nor by any other clockwork schedule. It keeps its own time, following a complex set of rules. Once you understand these rules, however, you find that Old Faithful really is faithful in its fashion. It announces its future plans by varying the size, duration, and intensity of its eruptions.

The intervals between eruptions average 79 minutes, but they have been known to range from about half an hour to a full two hours. In general, a powerful, long-lasting eruption is followed by a long rest period, and a brief eruption by a shorter one; but there are so many variations of this simple formula that books have been written on the subject. After each eruption, a park ranger, who has timed the play with a stopwatch and estimated the height, volume, and temperature of the water, posts a sign telling when the next eruption is likely to occur. The ranger is seldom more than 10 minutes or so off the mark.

The ground around the geyser's mouth is covered by a broad, gently sloping cone of pearly gray rock. The rock has two names: it is called either sinter or geyserite. It is made largely of silica, dissolved by hot water from stone deep beneath the ground, then carried up to harden upon the surface. Other minerals, especially sulfur and iron, sometimes add hushed tones of yellow, purple, rose, lavender, and other colors.

Tremendous quantities are involved; each time Old Faithful erupts, 65 pounds of silica spew up from its vent. At the same time, each eruption adds a thin coat to the inner walls of the underground plumbing. Someday even this most dependable of geysers will become clogged, and the water will have to find a new route upward. Perhaps a new geyser will be born, or perhaps the flow will be added to an existing pool or geyser.

Old Faithful is one of nearly 350 geysers in Yellowstone National Park. This is the world's largest collection, and it includes some that are bigger than Old Faithful, several that are more regular, and a few that are more spectacular, but none that combines the three elements in quite the same way. Although its pattern of behavior changed little for at least a century, making Old Faithful unique among geysers, it has shown signs of change in recent years.

The waters of Excelsior Geyser, once the largest in the park, used to shoot periodically more than 300 feet high. Its last eruption was in 1985, however; since then it has behaved like a hot spring, placidly pouring about 5.8 million gallons of scalding water every day from its gaping, steam-shrouded crater into the nearby Firehole River. Even so, no one can state with certainty that Excelsior will not resume its violent activity at any moment. Only a fool tries to second-guess a geyser.

Riverside Geyser, on the east bank of the Firehole, is at present more dependable than Old Faithful, but its main claim to fame is that it does not shoot straight up, as most geysers do. For about 20 minutes every 7 hours, it sends a beautiful 75-foot plume of water arching gracefully over the river.

Grotto Geyser is irregular but consistent; it plays about half the time, day in and day out, but you can never be sure exactly when it will do so. Though its streaming waters shoot only about 20 to 30 feet high, the eruptions are spectacular because of the fantastic, dwarfish shapes through which the water spurts. The geyser's cone is slowly building up around the twisted remains of trees that once grew in this spot; now, encased in geyserite deposits, they are bowed and bend over the mouth of the geyser, forming the eerie grotto for which it is named.

Some geysers are named for the distinctive cones that have built up around their vents. Beehive Geyser is one such; at irregular and unpredictable intervals a powerful stream of water squirts through the small hole in the top of its big, rounded cone, sometimes reaching heights of 200 feet. Castle Geyser, possibly the oldest in the park, has an architectural-looking cone that measures 120 feet around and is still growing. Its eruptions have two phases; first water is lifted about 80 feet high for as long as 20 minutes, then a jet of steam roars forth for about an hour.

Others, known as fountain geysers, have no cones. Great Fountain Geyser is the most spectacular of these; every nine hours or so several powerful bursts break the surface of the broad pool that covers its vent, scalding columns that may reach 200 feet in height.