File:Steamboat Geyser's south-draining runoff channel (6 August 2013) 4 (12729033915).jpg

Steamboat Geyser is located in the Back Basin of Yellowstone’s Norris Geyser Basin. Major eruptions of Steamboat Geyser are the tallest in the world. This feature first appeared on 11 August 1878 after a hydrothermal explosion. This was similar to, but larger than, the 5 September 1989 Porkchop Geyser hydrothermal explosion event, which occurred in the same geyser basin. Steamboat Geyser consists of two vents in a gentle hillside of rhyolitic ash-flow tuff (Lava Creek Tuff, lower Middle Pleistocene, 640 ka). Initially, the vents were powerful fumaroles that emitted steam and some mud. By 1879, moderately high to high geyser eruptions occurred. Small to large eruptions occurred at Steamboat Geyser from the late 1870s to the early 1910s. This was followed by 50 years of dormancy. Geyser eruptions resumed in the 1960s, followed by dormancy during the early and mid-1970s. More major eruptions occurred in the early 1980s, followed by sporadic to rare events from the mid-1980s to the 2000s. One major eruption occurred in May 2005. Others occurred at the end of July in 2013 and in September 2014. Steamboat entered an active phase in spring 2018 and was remarkable for having semi-regular major eruptions (about once a week) in May and June 2018.

Major eruptions of Steamboat Geyser have fountains of water reaching over 100 feet high. The highest have been close to 400 feet high - the highest on Earth. Major eruptions are normally not at regular intervals and thus are usually not predictable. The water phases of Steamboat’s major eruptions are about 3 to 40 minutes long, followed by hours of roaring fumarole activity (steam phase).