Victory Rock, the boys found, is a kind of bowsprit of lava thrust out from the rim, so that when you stand on it you can see almost all the circle of the lake, and the water appears to be directly under you.
“Now, take a good look,” Uncle Billy said, “and then try to imagine what this place was like before the big explosion. The rim here is 7,000 feet above sea level. In other words, we’ve climbed up, to get here, about half the height of the original mountain. We are about at snow line.”
“About!” Bennie laughed. “About is good!”
“Now just imagine the line of ascent we took from Government Camp carried right on up, all around the lake. When the slopes met, over the middle, in the peak of the original mountain, geologists reckon that peak was from 14,000 to 15,000 feet high. This was one of the highest mountains, if not the highest, in the United States proper. It was an active volcano, of course. If you’ll look over there to the northwest, you’ll see a big, steep precipice with a rounded top. That’s called Llao Rock. Do you see how the bottom of it curves up at either end? Well, that curve shows you where the bottom of a ravine was on the original mountain. In some eruption, ages ago, a great stream of lava flowed down that ravine, filled it up to overflowing, and hardened into rock. If you travel around the lake, you can pick out where each ravine was by the laval cliffs.”
“How high is that Llao Rock?” asked Spider.
“About 2,000 feet from the water.”
“Gee, then that lava stream was more’n a thousand feet deep!”
“It was,” said the doctor. “Much more.”
“And then what happened?” Bennie asked.
“Well, I wasn’t here at the time,” said Uncle Billy, “but as near as the scientists can figure it out, there must have been a tremendous eruption, scattering pumice all over Oregon and making a lot of our rich soil, and then, at the level where we are now, probably a lot of vent holes blew out, making the whole top of the mountain, which was only a shell around the great crater hole, so insecure that it just toppled inward of its own weight. About seven or eight thousand feet of the mountain just collapsed into the crater.”