Deschutes & Ochoco National Forests
Crooked River National Grassland

Oregon Volcanoes

Broken Top Volcano

SUMMARY

Type: stratovolcano
Activity: extinct
Last Eruption: estimated at about 100,000 yrs ago
Rock Type: predominantly basaltic andesite with interbedded andesite, dacite, and rhyodacite.
Eruptive Volume: ?
Latitude: 44.08 N
Longitude: 121.70 W
Location Maps: from TIGER Mapping Service

• State Level - shows state and communities
• County Level - shows county lines, highways, and communities
• Local Level - shows above plus lakes and local roads

Topo Map from TopoZone

Broken Top Photo Menu

GEOLOGIC BACKGROUND:

The Three Sisters area contains 4 large cones of Quaternary age -- North Sister, Middle Sister, South Sister, and Broken Top.

• North Sister and Broken Top are deeply dissected and probably have been inactive for at least 100,000 years.
• Middle Sister and South Sister are younger than the North Sister. They have both been erupting over the last 50,000 years.
• Middle Sister was active in late Pleistocene but not postglacial times.
• South Sister is the least dissected; its basaltic andesite summit cone has a well preserved crater. Most of South Sister predates late Wisconsin glaciation and is therefore older than 25,000 years; however, eruptions of rhyolite from flank vents have occurred as recently as 2000 years ago.

HISTORIC ACTIVITY:

• None

DATA SOURCE:

• USGS
  

ADDITIONAL INFORMATION

• Link to U.S.G.S. - CVO
  • Broken Top Info
  • Three Sisters Area Info
  • Volcano Hazards in the Three Sisters Region, Oregon
• Link to U.S.G.S. Visit a Volcano Info for Broken Top
• Link to University of Washington Geophysics Program Information
  • Three Sisters Seismicity Information
• Link to VolcanoWorld
  • Broken Top Info