Once upon a time, The Beatles lived in a Yellow Submarine. I, however, live inside a sunken volcano. It’s called the Crooked River Caldera.
Shortly after our arrival here, I’d heard people describe the country all around Prineville as a caldera, a volcano that blew up and then collapsed upon itself. I was more than skeptical at first; I was not convinced. There are a lot of calderas around the world, and you can see craters on the Moon, too. Crater Lake, in southwestern Oregon, is a classic example of a caldera (left). You can pretty readily see how the original volcano fell into itself and later became Crater Lake. I’ve been to Crater Lake, and It looks pretty big, too. That’s what I thought a caldera ought to look like.
Closer to us is the Newberry Volcano, with its own caldera. Not as clearly defined as Crater Lake, perhaps, but still pretty identifiable for what it is: a sunken volcano —>
Prineville’s surroundings don’t look like that. What I saw around Prineville just looked like a valley filled with river sediments that came from old lava flows, and there are a lot of THOSE around here. I didn’t see any features in the landscape that suggested a caldera. Well, I was wrong. (Click photos to enlarge).
The first hint was a public presentation on this topic scheduled in January by a local geologist that I immediately wanted to attend when I heard about it. It quickly sold out before I could obtain tickets for it. So I began my own research, and what I found is, well, a little astonishing.
Turns out that about 29 – 1/2 million years back, there were some big eruptions here. More than 139 cubic miles of ash and debris eventually filled the 25 x 17 mile elliptical caldera that formed afterward. Here’s an artist’s view of what that might have looked like . . . anyone see Jurassic Park here? Well, it was Eocene – Miocene times, but still pretty ancient.
All that makes the Crooked River Caldera, as geologists technically describe it, one of the largest known eruptions on Earth, even though its existence was only recently confirmed, apparently since its boundaries were unclear until modern geologic mapping and isotope-aging techniques made the clues come together convincingly, The enormity of the caldera certainly went beyond my comprehension at first. This thing is huge, larger than all of Lake Tahoe (a pretty big hole, but not a caldera) or Mammoth, California (which is one). On the whole planet, only six are larger, and two of those are at Yellowstone.
I needed to get my visual sense around this thing, more than by reading the Field Trip Guide (see link, above). Here’s what I came up with, using Google Earth: The best view of it, I learned, is from near the summit of Grizzly Mtn, northwest of Prineville (the green symbol at low center below).
The eastern boundary of the caldera (left on photo) is defined by the down-sloping foothills of the Ochoco Mtns. to our east, and I think the southern edge is approximately that dark, horizontal line of bluffs in the distance. While the western boundary of the depression has been buried under more recent lava flows from the south (Bend & Newberry areas), there sits Prineville almost in the center of it all.
Well, ain’t that somethin’!