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1/5th the World Geysers in a Square Mile

Hidden : 08/06/2007
2 out of 5
1.5 out of 5

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Geocache Description:

The upper geyser basin in Yellowstone has about 140 geysers within about 1 square mile. This is about 1/5th of the world’s active geysers. The formation of geysers requires a special combination of heat, ground water, and subsurface cracks. Ac???

The first component to create geysers is heat. This is provided by the cooling magma, which is between 3 and 8 miles below the surface. For magma, this is very close to the surface. Temperatures of 358 deg F have been measured at 500 feet below the ground in this basin.

The second component is water. Rain and snow melt percolate deep down into the ground in the surrounding mountains to form ground water. This water can flow down thousands of feet where it comes in contact with extremely hot rocks.

The third component is a series of fissures to bring the water back up to the surface, often called the plumbing. To form a geyser, there must be constrictions in the fissures that limit the flow of water.

Deep underground, the water is heated to temperatures that exceed the boiling point at this elevation (199 deg F; 93 deg C). Boiling can be described as the vaporization of a liquid and occurs when pressure to evaporate exceeds the surrounding pressure. (See Wikipedia for a start on a more detailed explanation)

At this altitude there is less atmospheric pressure, so water boils at less than 212 deg F (100 deg C). However deep underground, the weight of the rock and all the water in the fissures exerts quite a bit of pressure, allowing water to heat up to very high temperatures, 358 deg F at 500 below the ground, called super-heated water.

Small bubbles of steam form at these depths and begin rising up through the fissures. The bubbles expand as they rise up through the fissure as the pressure of the water decreases. These bubbles collect at one of the constrictions in the plumbing, and begin to lift the water above them up out of the plumbing. This reduces the pressure on the water below, quickly lowering the boiling point; causing the water below the bubbles to flash boil, ejecting out water in an eruption.

Yellowstone Digital Slide File, National Park Service;

The geyser eruption ends when the reservoir of water in the fissure has been exhausted or the steam bubbles pass through the constriction. Then ground water begins entering the fissures again to repeat the process.

Carried with the water are the minerals that the super-heated water from deep below the ground. In the upper Geyser Basin, the water below ground is flowing through rhyolite, a volcanic rock rich is silica and thus the water ejected from the geysers contains dissolved silica. On the surface, the water cools, forcing the dissolved silica to precipitate out of solution forming siliceous sinter or geyserite. Water can not dissolve much silica, so the geyserite deposits around the basin grow very slowly.

Logging requirements:
Send me a note with :

  1. The text "GC14YW1 1/5th the World Geysers in a Square Mile" on the first line
  2. The number of people in your group.
  3. Which is an older geyser, Old Faithful or Castle Geyser and explain why (read the info panel if you have a hard time)
  4. According to the NPS info panels, geysers can be placed into two categories, what are they and find an example of each from the Upper Geyser Basin.

The above information was compiled from the following sources:

  • NPS informational Pannel
  • Old Faithful Area Trail Guide Including Upper Geyser, Black Sand and Biscut Basins, Yellowstone National Park, Yellowstone Association, April 2007
  • Yellowstone Digital Slide File, National Park Service;
  • Fritz, William J., Roadside Geology of the Yellowstone Country, Mountain Press Publishing Company, May 1989.

Placement approved by the
Yellowstone National Park

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