English: Steamboat Geyser, northeastern Back Basin, southeastern Norris Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA on 9 August 2011.

Major eruptions at 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. Dormancy occurred 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. Another one occurred at the end of July in 2013. The most recent major eruption was in September 2014.

Major eruptions of Steamboat Geyser have fountains of water reaching over 100 feet high. The highest were close to 400 feet high - the highest on Earth. Major eruptions do not occur at regular intervals and thus are not predictable (decades ago, one woman waited 52 continuous days, hoping to witness a major eruption). Steamboat’s major eruptions are about 3 to 40 minutes long, followed by hours of roaring fumarole activity.

Normal activity at Steamboat Geyser consists of frequent splashing spouts (see above photo) that reach about 10 to even 60 feet high. Emitted water at Steamboat Geyser is somewhat acidic and quite hot.