Grotto Geyser, Yellowstone National Park Postcard

"Grotto Geyser, Upper Geyser Basin, Yellowstone National Park, Wyoming" by Catherine Sherman. Grotto Geyser, a fountain-type geyser, erupts in the Upper Geyser Basin in Yellowstone National Park, Wyoming. Grotto Geyser is one in a group of geysers that includes Grotto Fountain Geyser, South Grotto Fountain Geyser, Indicator Spring, Spa Geyser, Startling Geyser, and Rocket Geyser. Grotto Geyser's cone is nearly eight feet (2.4 m) high. The odd shape comes from geyserite accumulating over dead tree stumps as the geyser erupted. Geyserite, or siliceous sinter, is a form of opaline silica that is often found as crusts or layers around hot springs and geysers. Grotto Geyser erupts about every eight hours. The interval between eruptions is longer after a longer eruption. The eruptions are about 10 feet (3.0 m) high and can last from about one hour to more than 10 hours long, although there have been eruptions that lasted more than 26 hours. Grotto is significant beyond its own considerable size because of the interactions between its own eruptions and those of nearby Giant Geyser, one of the world's most powerful geysers. On September 18, 1870, members of the Washburn-Langford-Doane Expedition entered the Upper Geyser Basin where in a day and a half of exploration, they named seven geysers of which Grotto was one. Nathaniel P. Langford described the Grotto in his 1871 Scribner's account: "The Grotto" was so named from its singular crater of vitrified sinter, full of large, sinuous apertures. Through one of these, on our first visit, one of our company crawled to the discharging (opening); and when, a few hours afterwards, he saw a volume of boiling water, four feet in diameter, shooting through, it to the height of sixty feet, and a scalding stream of two hundred inches flowing from the aperture he had entered a short time before, he concluded he had narrowly escaped being summarily cooked. The discharge of this geyser continued for nearly half an hour.