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Geothermal areas of Yellowstone

There are six geyser basins in Yellowstone National Park and several other geothermal areas. The features found in these areas contain geysers, hot springs (including mud pots), and fumaroles. Many of these features build up sinter, geyserite or travertine deposits around and within them. Due to high elevation, the average boiling temperature at Yellowstone's geyser basins is 199 °F (93 °C). Water erupting from Yellowstone's geysers is superheated to an average of 204 °F (95.5 °C) as it immediately leaves the vent; the water cools significantly while airborne and is no longer scalding hot by the time it strikes the ground, nearby boardwalks, or even spectators.

Norris Geyser Basin is the hottest geyser basin in the park and is located near the northwest edge of Yellowstone Caldera near Norris Junction. Unlike most of other geyser basins in the park, the waters from Norris are acidic rather than alkaline. The difference in pH allows for a different class of bacterial thermophiles to live at Norris, creating different color patterns in and around the Norris Basin waters.

The largest geyser in the world is Steamboat Geyser and it is located in Norris Basin. Unlike the slightly smaller but much more famous Old Faithful Geyser located in Upper Geyser Basin, Steamboat has an erratic and lengthy timetable between major eruptions. During major eruptions, which may be separated by intervals of more than a year, Steamboat erupts over 300 feet into the air. However, Steamboat does not lie dormant between eruptions, but has minor eruptions of approximately 40 feet every few minutes.

South of Norris along the rim of the caldera is the Upper Geyser Basin, which has the highest concentration of geothermal features in the park. This complement of features includes the most famous geyser in the park, Old Faithful Geyser, as well as four other predictable large geysers. One of these large geysers in the area is Castle Geyser which is about 1400 feet northwest of Old Faithful. Castle Geyser has an interval of approximately 13 hours between major eruptions, but is unpredictable after minor eruptions. The other three predictable geysers are Grand Geyser, Daisy Geyser, and Riverside Geyser.

Further south is the Lower Geyser Basin, which has a much less concentrated set of geothermal features, including Fountain Paint Pots. Fountain Paint Pots are mud pots, that is, a hot spring that contains boiling mud instead of water. The mud is produced by a higher acidity in the water which enables the spring to dissolve surrounding minerals to create an opaque, usually grey, mud.

In the northwest corner of the park there is a large hot spring complex near Fort Yellowstone called Mammoth Hot Springs. Mammoth is a large hill of travertine that has been created over thousands of years as hot water from the spring cooled and deposited calcium carbonate (over 2 tons of calcium carbonate flows into Mammoth each day in a solution).

The hot water that feeds Mammoth comes from Norris Geyser Basin after traveling underground and through limestone (the limestone is the source of the calcium carbonate). Algae living in the warm pools have tinted that travertine shades of brown, orange, red and green.

Terrace Mountain at Mammoth Hot Springs is the largest known carbonate-depositing spring in the world. The most famous feature at the springs is the Minerva Terrace, a series of travertine terraces. The terraces have been deposited by the spring over many years, but due to recent minor earthquake activity, the spring vent has shifted, rendering the terraces dry.

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