Lava Flows

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

Volcanoes in the Three Sisters region have erupted a wide variety of magma types, therefore the shape, size, and impact of future lava flows could vary greatly.

The cluster of glaciated stratovolcanoes called the Three Sisters extends for 20 km (12 mi) along the crest of the Cascade Range in Oregon, 35 km (20 mi) west of the city of Bend and 100 km (60 mi) east of Eugene.

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

Broken Top is a long extinct volcano that was active in the middle Pleistocene between about 300 and 150 ka.

North Sister is the oldest and longest active volcano of the Three Sisters, and its period of construction from about 120 to 45 ka occurred after the eruptions of Broken Top ended.

The Three Sisters region has hosted volcanic eruptions for hundreds of thousands of years, and future eruptions are a certainty.