Yellowstone was set aside as the world’s first national park because of its hydrothermal wonders. The park contains more than 10,000 thermal features, including the world’s greatest concentration of geysers as well as hot springs, mudpots, and steam vents. Research on heat-resistant microbes in the park’s thermal areas has led to medical, forensic, and commercial uses. Oil, gas, and groundwater development near the park, and drilling in “Known Geothermal Resources Areas” identified by the US Geological Survey in Island Park, Idaho, and Corwin Springs, Montana, could alter the functioning of hydrothermal systems in the park. So in 1994, the National Park Service and State of Montana established a waterrights compact and controlled-groundwater area to protect those areas from development.
Under the Surface
The park’s hydrothermal system is the visible expression of the immense Yellowstone volcano; it would not exist without the underlying partially molten magma body that releases tremendous heat. The system also requires water, such as ground water 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, 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. The siliceous sinter deposits, with bulbous or cauliflower-like surfaces, are known as geyserite.
Explore Yellowstone's Hydrothermal Areas
Take a virtual tour around some of Yellowstone's more well-known hydrothermal areas.
Frequently Asked Questions
Yellowstone’s volcanic geology provides the three components necessary for the existence of geysers and other hydrothermal features: heat, water, and a natural “plumbing” system. Magma beneath the surface provides the heat; ample rain and snowfall seep deep underground to supply the water; and underground cracks and fissures form the plumbing. Hot water rises through the plumbing to surface as hydrothermal features.
A geyser basin is a geographically distinct area containing a “cluster” of hydrothermal features that may include geysers, hot springs, mudpots, and fumaroles. These distinct areas often, but not always, occur in low places because hydrothermal features tend to be concentrated around the margins of lava flows and in areas of faulting.
Small mudpot areas occur at West Thumb Geyser Basin, Fountain Paint Pot, and Artists’ Paintpots. The largest group of mudpots can be found at Mud Volcano, at the southern end of Hayden Valley.
Terrace Mountain, near Mammoth Hot Springs, is evidence of carbonate hot spring deposits up to 406,000 years old.
Norris Geyser Basin is the hottest and most dynamic of Yellowstone’s active hydrothermal areas. The highest temperature yet recorded in any Yellowstone hydrothermal area was measured in a scientific drill hole at Norris: 459°F (237°C) just 1,087 feet below the surface. Norris shows evidence of having had hydrothermal activity prior to the last great ice age. The features change often, with frequent disturbances from seismic activity and water fluctuations. Norris is so hot and dynamic primarily because it sits at the intersection of three major faults, two of which intersect with a ring fracture zone from the Yellowstone Caldera eruption of 640,000 years ago.
Yellowstone National Park’s hydrothermal resources cannot be tapped for geothermal energy because such use could destroy geysers and hot springs, as it has done in other parts of the world.
Dogs have died diving into hot springs. They also disturb wildlife and are prohibited from all park trails. In the few places pets are permitted, they must be leashed at all times. Ask at a visitor center where you can walk a pet.
YES. Geyser basins are constantly changing. Boiling water surges just under the thin crust of most geyser basins, and many people have been severely burned when they have broken through the fragile surface. Some people have died.
Cigarette butts quickly accumulate where smoking is allowed, and they—like any litter— can clog vents, thus altering or destroying hydrothermal activity.
The park’s hydrothermal areas are dispersed across 3,472 square miles (8,991 km2) making it challenging to coordinate a systematic monitoring program. Therefore, park geologist use remote sensing, groundwater flow studies, measurements from individual features, and collaboration with many other researchers to gather reproducible data over many years. The variety and duration of monitoring helps to distinguish human influences from natural changes, and define the natural variability of the hydrothermal system. This distinction is essential for Yellowstone to successfully protect the integrity of the system as a whole.
Hydrothermal variability is easiest to see in individual features. On March 15, 2018 Steamboat Geyser began a period of more frequent eruptions after three and a half years of dormancy. The world’s tallest geyser erupted 31 times in 2018, and 8 more times by March 5, 2019. Eruption intervals ranged from four to 35 days. The Upper Geyser Basin also experienced some increased activity around the Geyser Hill area in the fall of 2018. This includes new erupting vents splashing water on the boardwalks, surface fractures, and a rare eruption of Ear Spring on September 15, 2018. The eruption ejected a variety of foreign objects; coins and trash dating back to the 1930s. The Old Faithful eruption interval is 93 minutes as of March 2019.
These highly visible changes receive public attention, but do not necessarily represent changes in the entire hydrothermal system. New research methods and technology, further enhances our understanding. Work continues to progress documenting the status of the hydrothermal system by measuring the total amount of thermal water and the total heat output for selected geyser basins. Thermal infrared images taken by aircraft are used to document changes in the hydrothermal areas. Research measuring the seismic activity in the Upper Geyser basin used the “harmonic tremors” preceding eruptions to create three-dimensional images of geyser reservoirs and plumbing systems. This project produced the first three-dimensional seismic images of the Old Faithful plumbing system.
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Sedimentation and Erosion
The erosion of rock and the deposition of geologic material has created some stunning landscapes.
Fossil of plants, invertebrates, vertebrates, and trace fossils found within Yellowstone document 540 million years of life.
A volcano, geysers and other thermal features, earthquakes, and glaciers shape Yellowstone's landscape.
Last updated: August 6, 2019