Case Study: Diverse Origins of Two Caldera-forming Volcanoes in the Western U.S.

Altered rhyolites exposed in the Grand Canyon of the Yellowstone. Details
Yellowstone and Crater Lake National Parks feature a variety of well-studied volcanic rocks and other features associated with some of the most violent volcanic eruptions to have occurred in the western United States within the last 2 million years. Explosive eruptions of silicic magmas from these volcanoes produced vast deposits of ash which were spread across vast portions of the North American continent, dwarfing those associated with more recent volcanic eruptions in the western U.S., such as the 1980 eruption of Mount St. Helens. Particularly violent pyroclastic eruptions at these two volcanoes also produced calderas, collapse features produced by the suddent draining of large, sub-surface magma chambers.

Crater Lake Caldera. Details
While caldera-forming volcanoes are broadly similar in terms of their eruption behavior and volcanic deposits, the ultimate causes and eruptive behavior of caldera-forming volcanism are quite diverse, and are ultimately linked to plate tectonic setting. The volcanism at Crater Lake and Yellowstone highlight these differences and form the basis of this exercise.