- No matter what the name, or how it is used or abused, Bachelor is still a fine old volcano.
Bachelor wasn't alone in its violent and hot past. It belongs to a string of volcanic events about a mile and a half long, known geologically as the "Mount Bachelor Volcanic Chain" (MBVC).
If the volcano hadn't become an outstanding skiing area, it would probably still have its early name, "Bachelor Butte" as it was known when it was just a fair-to-middling shield volcano just across the Cascade Lakes Highway from Tumalo Mt.
The first time I made it to the top of Bachelor was with George Marshall, a great old Brooks-Scanlon timber-faller who has gone out among the stars. He invited me to accompany his family on a hike to the summit on a summer afternoon in 1953. We sat on the peak drinking tea, eating his wife's wonderul cookies, and watched the sun go down. Then we turned around and watched the moon come up over the Horse Heaven Hills. The enchanting hike down under the full moon was an experience I will never forget, and because of that empathy, it will always be "Bachelor Butte" to me...
Bachelor began its life around 18,000 years ago as a member of the MBVC. The Great Ice Age was retreating about the time Bachelor's shield volcano ancestors started erupting into several hundred feet of snow and ice covering older volcanic events along the Cascades skyline.
Sheridan Mountain was the first shield volcano to grow during the volcanic chain's early stages. There are lava caves near the slopes of Sheridan where I photographed the skeletal remains of a huge bear that experienced the Big Sleep in ancient times.
Several volcanic vents popped up in glacial lakes and deep snowfields occupying the site of present day Sparks Lake, throwing steam, cinder and blobs of lava into the frigid atmosphere. These events grew into lava flows that ate into glacial ice, leaving behind a steep-sided plateau where Talapus (Wolf) and Katsuk (Middle) Buttes are standing today.
As the MBVC continued to grow, Kwohl (Aunt) Butte and the shield volcano buried beneath Bachelor were going full blast. It was during this last stage of mountain building that the beautiful strato volcano we know today as Mt. Bachelor gained its full height.
Like many of the snow-capped volcanoes on the present High Cascade skyline, Bachelor is made of mostly basalt (basic rock), with small amounts of andesite basalt, ash and obsidian mixed in.
Basalt contains lots of iron, and, when it melts, it can flow like water (typical Hawaiian volcanic events). As the lava chamber matures, iron gives way to silica and begins to turn to andesite - thick, pasty lava that erupts more violently (Mt. St Helens).
In time, immeasurable heat and pressure essentially turn the volcanic chamber to silica that, in turn, reaches the surface as obsidian (volcanic glass), rhyolite flows, and explosive ash.
Some time long before Bachelor arrived on the scene, an enormous caldera, now buried under the Three Sisters, exploded repeatedly, hurling tons of ash and pumice onto Central Oregon. I had the pleasure of mining pumice for Bill Miller back in the 50s. Before that, Bend's early pioneers cut ancient tuff (baked ash covering the pumice) into blocks and used it to make their homes, shops and garages.)
The oldest glacial moraines on the slopes of Bachelor appear to be around 12,000 years old, indicating that the relative age of the summit cone.
The last significant eruption on Bachelor probably took place about 8,000 to 10,000 years ago, and produced a scoria (ash) cone and lava flows on the north flank. A visitor riding Summit chair lift in summer can see pillow lava remnants of those flows today.
According to evidence from C-14 samples, plus the vast amount of Crater Lake (Mt. Mazama) ash deposited on the slopes of old Bachelor, it's final volcanic gasp ended 6,845 years before present. In some geologist's books, the old volcano is "extinct," but those of us who hope for better things like to think of Bachelor as "dormant."