Three Sisters - Pacific Northwest Seismic Network

Three Sisters are a cluster of volcanoes, composed of North Sister, Middle Sister, and South Sister. They are located approximately 25 km SW of Sisters, OR.

North Sister is considered extinct, and Middle Sister has not erupted for 14,000 years. South Sister is the youngest volcano, and erupted explosively about 2,000 years ago. It has erupted lavas ranging from basaltic andesite through rhyolite. In 2001, uplift of almost 30 cm was detected in an area 5 km W of South Sister. This uplift was accompanied by a seismic swarm in 2004, raising concern of renewed activity. By 2007, uplift had slowed and seismic activity returned to background levels.

More information about Three Sisters

Background Seismicity

The Cascades Volcano Observatory, University of Oregon, and the PNSN cooperatively operate 10 seismometers on or near Three Sisters. On average, we locate 0 to 3 earthquakes within 10 km of the volcano each year.