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.
Opal Pool
The first recorded eruption of Opal Pool was in 1947, recurring in 1949, 1952 and 1953, then ceasing. Eruptions resumed in 1979, happening at least once in most following years. Eruption heights are typically under in height, but some eruptions have been seen with heights of to . Eruptions occur suddenly following visible convection in the pool, but are unpredictable. An eruption consists of one, huge, burst that throws water 20–80 feet high, making Opal Pool the largest active geyser at Midway Geyser Basin. Much smaller splashes seconds apart stretch the total duration to about 1 minute. In 2005 Opal completely drained, but refilled as a vivid green pool in 2008.