Ash/Tephra Fall

Three Sisters is a potentially active volcanic center that lies close to rapidly growing communities and resort areas in Central Oregon.

Eruptions from any volcano in the Three Sisters region, as well as from more distant volcanoes in the Cascade Range, are sources of potential tephra fall in Central Oregon communities.

South Sister is the southernmost and tallest of the Three Sisters. Early eruptions began between 50 to 45 ka, when South Sister produced numerous rhyolite lava flows and domes. Between 37 and 30 ka, the broad cone was built of rhyolite to andesite domes and flows, and construction of the cone ended with an explosive eruption that left pyroclastic deposi