Geyser
Yellowstone is the largest geyser locale, containing thousands of hot springs, and approximately 300 to 500 geysers. It is home to half of the world's total number of geysers in its nine geyser basins. It is located mostly in Wyoming, USA, with small portions in Montana and Idaho. Yellowstone includes the world's tallest active geyser (Steamboat Geyser in Norris Geyser Basin), as well as the renowned Old Faithful Geyser, Beehive Geyser, Giantess Geyser, Lion Geyser, Plume Geyser, Aurum Geyser, Castle Geyser, Sawmill Geyser, Grand Geyser, Oblong Geyser, Giant Geyser, Daisy Geyser, Grotto Geyser, the Fan & Mortar Geysers, & the Riverside Geyser, all in the Upper Geyser Basin which alone contains nearly 180 geysers.
Giant Geyser
Giant can go long periods between eruptions. Its activity level varies considerably from year to year. For several years starting in 1955 it was dormant, and from 1963 through 1987 only six eruptions were known to have occurred. By contrast, around 1997 the interval between eruptions averaged as little as four days. The most recent active phase of Giant Geyser started on August 6, 2005 and continued until April 29, 2008, when activity decreased dramatically; there was a single eruption again on August 26, 2008. There were 11 eruptions in 2005, 47 in 2006, 54 in 2007 (the most eruptions for any year since 1955), and 13 in 2008. There were no recorded eruptions in 2009 and 2 in January 2010. Giant Geyser erupted on September 28, 2015. Most recently, Giant Geyser erupted on July 24, 2018. The reasons for this variability are unknown.