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.
Tamu Massif
William Sager, a marine geophysicist from the Department of Earth and Atmospheric Sciences at the University of Houston, began studying the volcano in about 1993 at the Texas A&M College of Geosciences. According to Sager and his team, Tamu Massif is "the biggest single shield volcano ever discovered on Earth". While other igneous features on the planet are larger, such as the Ontong Java Plateau, it has not yet been determined if they are indeed just one volcano or rather complexes of several volcanoes.