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Discover the Geology of Old Faithful
One of the most popular tourist attractions in Yellowstone National Park is Old Faithful.
The geyser got its name for the primary reason it is such a draw – its eruptions are predicable,
making it easy to plan to see while visiting the park in northwestern Wyoming.
The National Park Service estimates Old Faithful will erupt approximately 17 times a day,
expelling 3,700 to 8,400 gallons of water (204°F) each time. Eruptions can be predicted
with a 90 percent confidence rate within a 10-minute variation. Scientists believe the
geyser’s predictability is due to it not being connected to any other thermal feature.
With more than 10,000 geysers and hot springs, Yellowstone is the world's
largest active geyser field because it is an active volcano with hot magma chambers
not far beneath the surface. This molten rock superheats groundwater; pressure begins to
build up and water turns to steam, filling the underground plumbing system of the geyser.
When the boiling water and steam reach the surface, they erupt into the air as a geyser.
Old Faithful is a cone geyser, which means it is visible on the earth's surface as a mound
of porous deposits of siliceous sinter. The water that erupts from Old Faithful reaches a
height of 106–184 feet, with an average near 130 feet, according to the National Park Service.
Yellowstone National Park lies within the Yellowstone Caldera, which was created by the most
recent massive eruption of Yellowstone Volcano approximately 640,000 years ago.
Old Faithful rests in the Upper Geyser Basin, where Yellowstone's largest concentration of hydrothermal features resides.
The basin is surrounded by relatively recent rhyolitic lava flows from a volcanic eruption, and
small earthquakes occur as frequently as 1,000 to 3,000 per year.
The University of Utah Seismograph
Station tracks this activity closely. Information about earthquakes in Yellowstone can also be found on the WSGS website.
See a webcam of Old Faithful.
More information about the geology in Yellowstone National Park can be found on the WSGS and National Park Service websites.
Geologic Map of the Old Faithful Quadrangle, Yellowstone National Park, Wyoming
National Park Service, [n.d.], Yellowstone National Park, ID, MT, WY, Frequently asked questions–Old Faithful Geyser, accessed
February 2017, at https://www.nps.gov/yell/learn/nature/oldfaithfulgeyserfaq.htm.
National Parks Trips Media, 2017, Yellowstone–About Old Faithful–The most famous geyser in the world, accessed February 2017, at
Wyoming State Geological Survey, 2017, Yellowstone, accessed February 2017, at
Yellowstone, 2017, 8 Best Yellowstone geyser basins and map, accessed February 2017, at
Christina George (307) 766-2286 Ext. 231