The Upper Geyser Basin

There is no other place on Earth like the Upper Geyser Basin here in Yellowstone National Park. The entire basin is about 2 miles long and ½ a mile wide and includes the features found at Black Sand Basin and Biscuit Basin as well as those found in the Old Faithful area. Of the world’s 600 geysers, nearly 150 are found in the Upper Geyser Basin.

Yellowstone contains over 10,000 thermal features, including geysers, hot springs, fumaroles and mudpots. That is more than the rest of the world combined. To understand why we find such a unique system of hydrothermal features here, we need to look at the regions geologic past.

Yellowstone National Park sits atop of one of the world’s largest volcanoes. This area has experienced 3 major volcanic eruptions in the last 2 million years. The last one was approximately 640, 000 years ago. That eruption created a caldera or crater that covers much of what is today Yellowstone National Park. The caldera is estimated to be 30 by 45 miles in size.

Later, rhyolitic lava flows filled most of the caldera. These lava flows provided silica, one of the key ingredients needed to form Yellowstone’s geysers and other thermal features. By adding heat and water, the stage is set for thermal features to develop.

The heat comes from a magma chamber that is quite near the surface beneath Yellowstone. It is believed to be 5 to 8 miles below the park. Water falling as rain and snow percolates down through cracks and fissures in the earth. As this heavy cool water sinks it creates convection currents with the lighter heated water. That heated water begins its long journey back toward the surface. Due to the pressure created by overlying rock, this silica rich water can reach temperatures above 400 degrees F without boiling.

This superheated water holds silica in solution. As the water rises, it begins to cool and some of those minerals begin to precipitate out and coat the inside of the network of underground fissures and channels. Over time, these natural plumbing systems provide a path for the hot water traveling toward the surface.

When this happens, hot springs can develop. The temperature in Yellowstone’s hot springs can be anywhere from luke-warm to above boiling. As the water runs off and cools, silica precipitates out and forms aprons of white rocks called siliceous sinter that you see on the webcam.

This process of silica precipitating out of solution is also responsible for the development of geysers. Silica coats the walls of cracks and fissures, creating a nearly pressure-tight seal. Over time, constrictions can form in these plumbing systems, which allow pressure to build.

As the pressure builds, geysers can begin to overflow or toss small jets of steam and water; this action is called pre-play. When this happens, the pressure on the superheated water below drops and some of that water expands into steam. When water turns to steam, it expands up to 1500 times. This powerful steam pocket rises to the surface and all the water above is thrown into the air. There are 2 types of geysers: fountain and cone. Fountain geysers erupt out of a pool of water and cone geysers, like Old Faithful, erupt out of a geyserite cone.

If all the water in a feature is far below ground level, that feature is called a fumarole. Also known as a steam-vent, they can be the hottest of the hot. The small amount of water that does exist is heated by rocks and the resulting steam rises through the plumbing system.

It is possible to see many of the world’s largest geysers from our new camera; Old Faithful, Beehive, Grand, Daisy, Lion, Giant and Giantess will all be in view at times, along with many smaller geysers. Old Faithful, the closest geyser to the camera has an average interval between eruptions of around 90 minutes.

Old Faithful’s eruption averages around 130 feet in height, but ranges from 106 to 180 feet. Eruption times are predicted whenever the Old faithful Visitor Center is open. Those predictions are posted on our original Old Faithful webcam.

Be sure to visit our Inside Yellowstone and Yellowstone InDepth videos to learn more about Yellowstone’s issues, features, and processes. They are available under Photos and Multimedia on the Official Yellowstone National Park web site, www.nps.gov/yell/.