Hydrothermal Systems and How They Work
With half of the earth's geothermal features, Yellowstone holds the planet's most diverse and intact collection of geysers, hot springs, mudpots, and fumaroles. More than 300 geysers make up over one half of all those found on earth. Combine this with more than 10,000 thermal features comprised of brilliantly colored hot springs, bubbling mudpots, and steaming fumaroles, and you have a place like no other. Geyserland, fairyland, wonderland--through the years, all have been used to describe the natural wonder and magic of this unique park that contains more geothermal features than any other place on earth.
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.
Descriptions and explanations of the processes involved in the functioning of the following geothermal features are just a click away.
Technical information is available from these Non-NPS sources.