Yellowstone Hot Springs
In the high mountains surrounding the Yellowstone Plateau, water falls as snow or rain and slowly percolates through layers of porous rock, finding its way through cracks and fissures in the earth's crust created by the ring fracturing and collapse of the caldera. Sinking to a depth of nearly 10,000 feet, this cold water comes into contact with the hot rocks associated with the shallow magma chamber beneath the surface. As the water is heated, its temperatures rise well above the boiling point to become superheated. This superheated water, however, remains in a liquid state due to the great pressure and weight pushing down on it from overlying rock and water. The result is something akin to a giant pressure cooker, with water temperatures in excess of 400°F.
The highly energized water is less dense than the colder, heavier water sinking around it. This creates convection currents that allow the lighter, more buoyant, superheated water to begin its slow, arduous journey back toward the surface through rhyolitic lava flows, following the cracks, fissures, and weak areas of the earth's crust. Rhyolite is essential to geysers because it contains an abundance of silica, the mineral from which glass is made. As the hot water travels through this "natural plumbing system," the high temperatures dissolve some of the silica in the rhyolite, yielding a solution of silica within the water.
At the surface, these silica-laden waters form a rock called geyserite, or sinter, creating the massive geyser cones; the scalloped edges of hot springs; and the expansive, light- colored, barren landscape characteristic of geyser basins. While in solution underground, some of this silica deposits as geyserite on the walls of the plumbing system forming a pressure-tight seal, locking in the hot water and creating a system that can withstand the great pressure needed to produce a geyser.
With the rise of superheated water through this complex plumbing system, the immense pressure exerted over the water drops as it nears the surface. The heat energy, if released in a slow steady manner, gives rise to a hot spring, the most abundant and colorful thermal feature in the park. Hot springs with names like Morning Glory, Grand Prismatic, Abyss, Emerald, and Sapphire, glisten like jewels in a host of colors across the park's harsh volcanic plain.
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