Old Faithful geyser erupting

Yellowstone: Old Faithful

This is the first of a series of posts about geologic features we saw in Yellowstone National Park during our June vacation in Grand Teton and Yellowstone National Parks.

Toward the end of our week in Yellowstone, we returned to the Old Faithful area to see geysers and other features related to hot water. Yellowstone was formed due to volcanos and has the most geysers in the world, more than Iceland or New Zealand.

This diagram shows the cycle of water in these hydrothermal features. The blue arrows down the sides of the diagram show surface water from rain or snow being absorbed into the ground. This ground water is heated by the magma close to the earth’s surface. The heated water, shown as red and blue arrows, tries to expand and migrates to cavities or or porous rock, creating pools of boiling water. The pressurized water finds a channel to the earth’s surface. If the channel is narrow, water will occasionally spurt out, forming a geyser.

Yellowstone's hydrothermal features
Yellowstone’s hydrothermal features

In the geyser photo above, note the white mound around the geyser. It’s a feature of a cone geyser, which forms a cone around the geyser opening. Cone geysers function like a nozzle spouting water. Deep in the earth, heated water dissolves and transport silica, the same mineral found in sand and glass, to the surface. During geyser eruptions, silica is deposited around narrow vents or opening. Over time, this mineral, called geyserite or sinter, forms mounds of varying sizes and shapes.

Old Faithful is named because it erupts faithfully, on a uniform period between eruptions. When we arrived at Old Faithful, we looked at the prediction for the next eruption and found we had some time. We walked to the nearby Old Faithful Inn, the largest log structure in the world, and marveled at the stone fireplace and logs. We don’t see stone fireplaces this tall in California, earthquake country. With the volcanism in Yellowstone, they do have earthquakes. Perhaps the fireplace has been rebuilt to seismic standards in the 100+ years since it was built.

Old Faithful Inn lobby
Old Faithful Inn lobby

Watching the time, we found a place near Old Faithful in time to enjoy the geyser erupt. Here’s our video.


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I enjoy travel, art, food, photography, nature, California native plants, history, and yoga. I am a retired software engineer. The gravatar is a Nuttall's woodpecker that visited our backyard.

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