Deschutes & Ochoco National Forests
Crooked River National Grassland

Oregon Volcanoes

Mt. Bachelor Volcanic Chain

SUMMARY

Type: chain of shield volcanoes and cinder cones
Activity: extinct
Last Eruption: about 8,000 years ago
Rock Type: basalt to basaltic andesite
Eruptive Volume: 30 to 50 cu km
Latitude: 43.795 N to 44.014 N
Longitude: 121.645 W to 121.697 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

Latitude (Mt. Bachelor): 43.98 N
Longitude (Mt. Bachelor): 121.68 W

Topo Map from TopoZone

Mt. Bachelor Volcanic Chain Photo Menu

GEOLOGIC BACKGROUND:

The 15 mile long Mount Bachelor volcanic chain is composed of numerous cinder cones and lava flows and three shield volcanoes. The northernmost shield is capped by a steep-sided summit cone of Mount Bachelor. Minor explosive activity built the many cinder cones which fed the many lava flows that account for the bulk of the erupted material.

Eruptive activity of the chain can be divided into four episodes:

1. The oldest episode occurred approximately 18,000 - 15,000 years ago during glacial retreat. Most activity during this episode was located in the central part of the chain and built a shield volcano called Sheridan Mountain. In an area near Sparks Lake a group of vents formed beneath glacial ice and interacted with the ice to form hyaloclastite deposits and thick lava flows impounded by glacial ice.  The resulting steep sided plateau is capped by Talapus and Katsuk Buttes.
2. During the second episode, eruptive activity was along the chain of scoria cones and lava flows that extends from the south side of Sheridan Mountain to the explosion crater at the south end of the chain.
3. During the third episode of eruptive activity built the shield volcano of which is capped by Kwohl Butte and the shield that underlies Mount Bachelor. The final phase of this episode built the summit cone of Mount Bachelor. The oldest glacial moraines recognized on Mount Bachelor are approximately 12,000 years old so the cone had nearly attained its present size by then. These moraines are overlain by the youngest lava flows of the third episode.
4. The last eruptive episode occurred approximately 8,000 to 10,000 years ago and produced a scoria cone and lava flows on the lower north flank of Mount Bachelor. All activity ended before 6,845 C-14 years BP, since tephra from the climactic eruption of Mount Mazama is found on all deposits of the Bachelor chain

HISTORIC ACTIVITY:

• None

DATA SOURCE:

• USGS
  

ADDITIONAL INFORMATION

• Link to U.S.G.S. - CVO's Mt. Bachelor Info
• Link to U.S.G.S. Visit a Volcano Info for Mt. Bachelor
• Link to Volcano World's Mt. Bachelor Info