The summit of Mount Bachelor is composed of numerous vents that erupted short, blocky basaltic-andesite lava flows.
![Mount Bachelor viewed from the south. Sparks Lake and South Sister...](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/side_image/public/vhp_img1253.jpg?itok=L7iK3C91)
The summit of Mount Bachelor is composed of numerous vents that erupted short, blocky basaltic-andesite lava flows. The summit vents and plugs exposed in the headwall of the cirque on the northeast side of the summit and are arrayed in a northwest-southeast-trending cluster that forms an elongate summit ridge. Near-vent tephra falls are scarce, which suggests that the most of the summit cone was built by lava flows, with minor explosive activity. From the summit of Mount Bachelor, a visitor can look south and see the extent of the volcanic chain as a line of volcanic events as far as Lookout Mountain.
The summit of Mount Bachelor is composed of numerous vents that erupted short, blocky basaltic-andesite lava flows.
![Mount Bachelor viewed from the south. Sparks Lake and South Sister...](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/side_image/public/vhp_img1253.jpg?itok=L7iK3C91)
The summit of Mount Bachelor is composed of numerous vents that erupted short, blocky basaltic-andesite lava flows. The summit vents and plugs exposed in the headwall of the cirque on the northeast side of the summit and are arrayed in a northwest-southeast-trending cluster that forms an elongate summit ridge. Near-vent tephra falls are scarce, which suggests that the most of the summit cone was built by lava flows, with minor explosive activity. From the summit of Mount Bachelor, a visitor can look south and see the extent of the volcanic chain as a line of volcanic events as far as Lookout Mountain.