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.
Ushishir
These islets are the tops of a partially submerged volcano. The southern island, Yankicha (), consists of the summit caldera and has a maximum width of . The caldera has a diameter of , and is breached on the south, forming a sea-water crater bay. The bay has an estimated depth of , and there is strong evidence of ongoing underwater volcanic activity, as evidenced by frequent bubbles, altered water chemistry and the presence of bacteria mats. Two small lava domes for small islands in the central lagoon, and numerous fumaroles and hot springs are along the southeast caldera shoreline. The island’s highest point is high, and is on the eastern shore.
The northern islet (Ryponkicha ) is the larger of the two, and consists of a portion of the volcano’s flank, with sheer cliffs rising up from the sea. 
Ushishir is still an active volcano with the last known eruption in 1884.