On a similar vein, the Yellowstone National Park is also best known for its various geysers, the most famous of which is Old Faithful. But what makes water in this kind of place gush from the ground? Geysers are not common. In fact, there are only approximately 1,000 geysers around the world and more than one-half of these geysers can be found in Yellowstone National Park (Glennon, 2005). For geysers to occur, three components must be met. First, there must be abundant supply of water. Then there has to be an intense source of heat. And finally, there has to be a unique plumbing system.
Geysers is in a way similar to hot springs, except that with geysers, the water shoots up from the ground. What differentiates geysers from ordinary hot springs is the plumbing, which should be water- and pressure-tight. The plumbing is made from rhyolite, which is high in silica and is effective in hosting geysers. Rhyolite, which is a volcanic rock, is capable of forming a water-tight seal along the walls of the plumbing. It is for this reason that most of the geysers in the world can be found in rhyolite or similar silica-filled rocks such as ignimbrite (Glennon, 2005).
The heat, in this case, is supplied by the magma chamber. Water supply comes from rain or snow that seeps down from the surface through fractures in the rock. “As the water reaches hot rock, it begins to rise back to the surface, passing through rhyolite…. The hot water dissolves the silica [in rhyolite] and carries it upward to line rock crevices. This forms a constriction that holds in the mounting pressure, creating a geyser’s plumbing system” (Yellowstone National Park, 2004).
The water heated by magma rises back to the surface through the process of convection. This water is many degrees above the boiling point, so some of it turns into steam. Meanwhile, cool water continues to seep through the porous rocks near the ground to mix with the hot water. Expanding steam bubbles formed at depth rise and meet the cooler water, filling the plumbing system. As they meet, the cooler water gets heated until the rising bubbles manage to heat the surface water until it reaches boiling point.
At this point, the system acts just like a pressure cooker. Here, the water is above the boiling point but it remains liquid because of the continuous pressure from the water above. This is because the boiling point of a liquid is dependent on the pressure exerted (Bryan, 2001, p. 472). The process of filling and heating water continues until the plumbing system is full or nearly full, and when it gets filled, the geyser is ready for an eruption. Essential to the eruption is the adequate heating by the magma that should occur alongside with the filling of water.
Each geyser is very different from another geyser. For instance, one geyser may take only a few seconds to fill and then erupt, while other larger geysers may take several days to fill. Others may also fill easily before they get hot enough to erupt, so they overflow even before the eruption. Other geysers, on the other hand, may be heated easily and begin an eruption even before getting filled with water. As the water in the plumbing system gets heated to boiling point, the rising steam bubbles no longer collapse near the surface.
Initially, the bubbles make it to the surface, but as more water continues to fill in, be heated and rise, it comes to a point where the mass of water will be constricted or meet a bend in the plumbing. The water then tries to squirt through the narrow path, forcing some water out of the geyser. This lowers the pressure and thereby reducing the boiling point of the water, which is already hot enough to boil. Eventually, the eruption occurs as the steam expands to more than 1,500 times its volume. The boiling quickly becomes violent that the water shoots up.
This eruption lasts until the temperature drops or until there is no more supply of water. Afterwards, the entire process is repeated until the geyser erupts again (Bryan, 2001, p. 472). There are two general types of geysers: one is a “fountain geyser,” which erupts from pools of water in intense, violent bursts, and the other type is a “cone geyser,” which erupts from cones of siliceous sinter, usually lasting from a few seconds to several minutes. In Yellowstone National Park, the most famous geyser, Old Faithful, is an example of a cone geyser.
There are other geysers in the park, including the Riverside Geyser, which erupts at an angle, creating a sort of rainbow in its mist. Castle is also a cone geyser and its cone is shaped like a medieval castle… thus the name. Grand Geyser erupts in powerful bursts that can go higher than the surrounding trees. Echinus spouts up and out to all sides like a fireworks display of water. Steamboat is the largest geyser in the world, bursting like a massive steam engine and reaching heights of 300 to 400 feet (Yellowstone National Park, 2004).