Poster Castle Geyser at Sunset, Yellowstone National Park

"Castle Geyser at Sunset, Yellowstone National Park, Wyoming" by Catherine Sherman. Castle Geyser is steaming in a serene landscape of Yellowstone National Park with a forest in the background, under a partly cloudy sky at sunset. The steam creates a dramatic contrast against the colorful sky. Castle Geyser, a cone geyser not far from Old Faithful Geyser in the Upper Geyser Basin of Yellowstone National Park, Wyoming, erupts every ten to twelve hours. This geyser stands out because of its large geyserite sinter deposits, which form its cone. The geyser was named in 1870, when the cone's top edges resembled a castle, with a large keep, multiple turrets, and crenellation along the top edges. Successive eruptions since that time have changed the cone's shape. Castle Geyser erupts hot water for about 20 minutes in a vertical column that reaches a height of 90 feet (27 m) before changing to a noisy steam phase that issues for 30 to 40 minutes. The sinter cone for Castle Geyser has been dated to around the year 1022, using carbon-14 dating. If you're lucky, you'll you will get to the geyser when it's about to erupt, so it only erupts about twice a day. If you're even luckier, you can see a rainbow when the Castle erupts. The geothermal areas of Yellowstone include several geyser basins as well as other geothermal features such as hot springs, mud pots, and fumaroles. The number of thermal features in Yellowstone is estimated at 10,000, and 200 to 250 geysers erupt in Yellowstone each year, making it the place with the highest concentration of active geysers in the world, thanks to its location in an ancient active caldera.