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.
Three Sisters (Oregon)
South Sister, also known as "Charity", is the tallest volcano of the trio, standing at . The eruptive products range from basaltic andesite to rhyolite and rhyodacite. It is a predominantly rhyolitic stratovolcano overlying an older shield structure. Its modern structure is no more than 50,000 years old, and it last erupted about 2,000 years ago. Although its first eruptive events from 50,000 to 30,000 years ago were predominantly rhyolitic, between 38,000 and 32,000 years ago the volcano began to alternate between dacitic/rhyodacitic and rhyolitic eruptions. The volcano built a broad andesitic cone, forming a steep summit cone of andesite about 27,000 years ago. South Sister remained dormant for 15,000 years, after which its composition shifted from dacitic to more rhyolitic lava. An eruptive episode about 2,200 years ago, termed the Rock Mesa eruptive cycle, first spread volcanic ash from flank vents from the south and southwest flanks, followed by a thick rhyolite lava flow. Next, the Devils Hill eruptive cycle consisted of explosive ash eruptions followed by viscous rhyolitic lava flows. Unlike the previous eruptive period, it was caused by the intrusion of a dike of new silicic magma that erupted from 20 vents on the southeast side and from a smaller line on the north side. These eruptions generated pyroclastic flows and lava domes from vents on the northern, southern, eastern, and southeastern sides of the volcano. These relatively recent, postglacial eruptions suggest the presence of a silicic magma reservoir under South Sister, one that could perhaps lead to future eruptions.