Three Sisters (Oregon)

Three Sisters, view from southeast


The Three Sisters (English Three Sisters ) are three volcanic peaks in the central part of the Cascade Range in the state of Oregon, USA.

They rise in the Three Sisters Wilderness Area, a 979 km ² large wilderness area, which lies within the national forests Willamette and Deschutes .. The three peaks are eponymous for the surrounding 809 km ² Three Sisters Biosphere Reserve.


The name Three Sisters first appeared on Preston's Map of Oregon in 1856. Should Back in the early 1840s, according to the records of a mission of the Methodist Church in Salem, the three peaks from north to south Faith (belief ), Hope (Hope) and Charity ( charity) have been called.

The three volcanoes have received their common name because they are so close together and act as a unit. The nearby Mount Bachelor ( Bachelor ) got its name in reference to this phenomenon; it rises to a certain distance to the Three Sisters and makes a comparatively lonely impression.

Geology and volcanic activity

North Sister

The North Sister ( 3074 m) is the oldest of the three volcanoes with towering spiers and glaciers. The last eruption of the shield volcano took place during the late Pleistocene, which is why he is regarded as having lapsed. The North Sister has more Dykes as any comparable peaks of the Cascade Range. The body of rock were pushed aside by the present summit cone. Part of the cone are the two highest points of the volcano called Prouty Peak and South Horn. The ascent of the mountain is due to the rockfall dangerous than the other two of the Three Sisters. The saddle height is 831 m.

Middle Sister

The Middle Sister ( 3062 m) is the smallest and least explored mountain under the Three Sisters. The summit area was originally conical, but especially the east side was formed by glaciers. The stratovolcano consists mainly of basalt, but also includes andesite, dacite and rhyodacite on. The Middle Sister is considered extinct, because the last eruption took place about 50,000 years ago. The volcano is younger than North Sister and slightly older than the South Sister. Due to its location between the other two, the Middle Sister has the lowest saddle height with 344 m.

South Sister

The South Sister ( 3159 m) is of all the most recent and highest volcano. The volcanic rocks are basaltic andesite, rhyolite and rhyodacite. At last he broke out about 2000 years ago. In its crater is the permanently frozen teardrop pool, the highest lake in Oregon. Near the summit are two comparatively small glaciers, named they are according to Lewis and Clark. For the ascent of the mountain hikers enough a day hike. Popular starting points are the Green Lakes and Devil's Lake. The saddle height is 1706 m.

In 2001 arose satellite images show the changes in the earth's surface in the form of elevations five kilometers south of the South Sister summit. The deformations indicate a possible awakening of the volcano in the near future. It is also to suggest that magma to the surface to cool before exiting through increased contact with solid rock and is braked. Further observations have shown that with an increasing activity less of the main crater, but rather other bodies break out on the hill.


Middle Sister from North West

South Sister from the air

The Three Sisters in December 2008