Grand Geyser is a fountain geyser located in the Upper Geyser Basin of Yellowstone National Park in the United States. It is the tallest geyser that erupts regularly. The geyser was named by Ferdinand Vandeveer Hayden in 1871.

Eruptions

Grand's fountain can reach up to 200 feet (61 meters) high, and each eruption lasts between 9 to 12 minutes. During an eruption, it usually has 1 to 4 bursts (sometimes up to 5).

Sequence

Grand erupts every 4 to 8 hours. It is part of the Grand Group (or Grand Geyser Complex), and its eruptions are related to those of other geysers in the group, especially the nearby Vent Geyser and Turban Geyser.

A few hours before Grand erupts, Turban Geyser erupts for five minutes every 17 to 22 minutes. Grand’s eruption usually begins 1 to 2 minutes after Turban starts erupting. Sometimes, Grand erupts just before Turban begins, and Vent Geyser erupts shortly after Grand starts. Occasionally, Grand stops erupting after 7 to 9 minutes, then restarts with a taller fountain a minute or two later. Grand may restart up to more than six times during one eruption. After Grand stops erupting, Vent and Turban may continue erupting for about an hour. As of 2018, Grand Geyser has become very predictable, with nearly every eruption happening about 6 to 7 hours apart.

After each eruption, Grand’s pool is empty and takes about five hours to refill.