Get to know Castle Geyser

Castle Geyser is one of the major geysers in the Upper Geyser Basin, and its eruptions are predicted. Generally, Castle Geyser can erupt once a day during daylight hours. In this article, we’ll look at this impressive geyser.

THE BASICS OF CASTLE GEYSER

• Usually erupts every 12-14 hours (unless it has a minor eruption).
• Erupts to about 100 feet, but many bursts are less than that.
• Major eruptions can last up to an hour (including the steam phase), and Minor eruptions stop abruptly during the water phase.
• Castle Geyser is a short walk from Old Faithful.

WHERE IT’S LOCATED

Castle Geyser is a short walk down the paved walking/bike path from Old Faithful. One of the best things about waiting for Castle Geyser are the benches in the shade of the trees that also allow you a view toward Grand Geyser and Geyser Hill. It’s a nice place to keep an eye on quite a few geysers from a shady spot.

In addition, when the sun is lower, you have the potential to see rainbows in the spray from the steam. Given that the boardwalk allows us to see it from many angles, it increases the ability to get into the right spot for rainbows.

HOW ERUPTIONS HAVE CHANGED OVER TIME

Castle Geyser has a unique and large cone that’s unmistakable. It was named by members of the Washburn party in 1870 because the shape of the cone resembles a castle turret. Carbon dating and 3D laser scanning (research conducted by geologist Duncan Foley) show that the cone was built over four or five different stages over about a thousand years. This illustrates that one of the only constants with geysers is change. If you look at the base of the cone, you’ll see more horizontal layers of sinter (the name of the rock). This indicates smoother overflow. It takes splashes from the eruptions to create the bumpier texture.

Reports from the first few decades of Yellowstone’s existence as a National Park show Castle exhibiting various behaviors, from splashing nearly continuously to major eruptions once every 4 to 8 weeks to erupting once daily. Different heights have also been reported, from 30-50 feet splashing to powerful full eruptions like we enjoy today.

HOW TO WATCH FOR AN ERUPTION

A few hours before an eruption, occasional splashes rise above the cone. While these preplay splashes signal that water has refilled the system, it may still be a few hours until the eruption. Check for a prediction time for Castle with the
National Park Service or Geyser Times.

At times, you may not find a prediction. That’s because Castle Geyser has both major and minor eruptions, and the minor eruptions throw the system off. The difference between major and minor eruptions depends on the length of the eruption and, more importantly, if the eruption ends with a steam phase.

Major eruptions usually start with an extra-large splash that suddenly shoots up to 100 feet skyward. During the water phase of the eruption, it might look like Castle has stopped, only to shoot skyward again. The water phase of the eruption will last anywhere from 10-20 minutes and then shift over to a loud steam phase. This steam phase can last a long time, making the entire eruption last about an hour.

Minor eruptions start exactly like major eruptions except they suddenly quit during the first 15-20 minutes of the water phase. Because this eruption uses a portion of the water and energy, it takes longer for the system to recharge.
If you have two minors in a row (back to back minors), then all bets are off for when the next major eruption might occur. But once you have a major eruption, the formula used for the predictions works again.

IN CONCLUSION

Castle Geyser is lovely to see erupting, but just seeing the cone is worth the short walk down the paved walking/bike path. If the prediction time is a ways off, consider wandering the rest of the geyser basin.

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