The Three Sisters volcanoes in Oregon are named Charity (South Sister), Hope (Middle Sister) and Faith (North Sister) by the early settlers.
The Three Sisters were formed at different times by different types of magma.
North Sister (3,074 m or 10,085 ft) is a long-lived basalt-to-andesite volcano that last erupted about 55 ka.
Middle (3,062 m or 10,047 ft) and South Sister (3,157 m or 10, 358 ft) began to grow around the same time, but South Sister erupted primarily rhyolite and dacite, whereas Middle Sister erupted primarily andesite and dacite except for an early high-silica rhyolite. The abundance of rhyolite lava at the two younger Sisters is unusual among Cascade stratovolcanoes.
See Geology and History Summary for Three Sisters to learn more.
Charity (South Sister) is the youngest, geologically speaking having the most recent volcanic activity of the Three Sisters.
Hope (Middle Sister) is shortest of a series of 3 volcanic peaks. The easiest route is the North Ridge Route which is accessed via Hayden Glacier on the east side and Collier or Renfrew Glaciers on the west side.
Faith (North Sister) is the most rugged and considered the hardest climb of the Three Sisters in central Oregon. It also could be considered one of the hardest of the Cascades volcanoes when comparing "standard" routes. It's the oldest and least climbed of the Three Sisters.
Check out tips on how to stay safe during a volcanic eruption, shared by National Geographic.