Yellowstone’s hydrothermal features would not exist without the underlying magma body that releases tremendous heat. They also depend on sources of water, such as from the mountains surrounding the Yellowstone Plateau. There, snow and rain slowly percolate through layers of permeable rock riddled with cracks. Some of this cold water meets hot brine directly heated by the shallow magma body. The water’s temperature rises well above the boiling point but the water remains in a liquid state due to the great pressure and weight of the overlying water. The result is superheated water with temperatures exceeding 400°F.
The superheated 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 journey back to the surface following the cracks and weak areas through rhyolitic lava flows. This upward path is the natural “plumbing” system of the park’s hydrothermal features.
As hot water travels through this rock, it dissolves some silica in the rhyolite. This silica can precipitate in the cracks, perhaps increasing the system’s ability to withstand the great pressure needed to produce a geyser.
At the surface, silica precipitates to form siliceous sinter, creating the scalloped edges of hot springs and the seemingly barren landscape of hydrothermal basins. When the silica rich water splashes out of a geyser, the siliceous sinter deposits are known as geyserite.
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