This image of Crater Lake, shot with my point-and-shoot camera, doesn’t come close to conveying the numinous power of this place – not even the finest photography can do that.

Nobody’s captured the feeling here better than the geologist Clarence Dutton, in a letter to the journal Science more than 130 years ago:

As the visitor reaches the brink of the Cliff, he suddenly sees below him an expanse of ultramarine blue of a richness and intensity which he has probably never seen before, and will not be likely to see again.

It is deeper and richer than the blue of the sky above on the clearest day. Just at the margin of the lake it shades into a turquoise, which is, if possible, more beautiful still. Ordinarily the water surface is mirror-like, and reflects an inverted image of the surrounding cliffs in detail. On the west side they reach their greatest altitude, rising almost vertically more than 2,000 feet above the water.

It was touching to see the worthy but untutored people, who had ridden a hundred miles in freight-wagons to behold it, vainly striving to keep back tears as they poured forth their exclamations of wonder and joy akin to pain.

The poetic geologist spent about a month exploring the lake by rowboat and making observations about the forces powerful enough to create such a landscape. He knew “almost at the first glance” that long ago the gigantic crater had been occupied by a mountain – later given the name Mazama – “rising far above the loftiest point of its encircling walls.” The pre-collapse summit elevation of Mount Mazama was about 3,650 meters, comparable to Mount Adams, according to modern estimates.

Dutton understood that a volcanic eruption had reduced the mountain, he just couldn’t decide what type of eruption. Was it formed like the sunken calderas of Hawaiian volcanos, with lavas oozing from below and causing the top to sink? Or was it catastrophic like Tambora on the island of Sumbawa, Indonesia, which blasted apart in a single horrific night on April 10, 1815?

He seemed to favor the latter explanation but couldn’t quite commit to it. Consistent with an explosive eruption, Dutton noted the scattering of volcanic pumice in a rough circle up to 60 miles in diameter around Crater Lake. He also found no traces of sinkage in the vicinity that would indicate a Hawaiian-style volcano.

“But there is a weak point in the argument,” Dutton wrote. “If a large cone, composed of solid lavas such as are now seen in the walls of the lake basin, has been blown into rubble, and the fragments hurled far and wide over the surrounding country, ought we not to be able to recognize them in vast abundance in the vicinity? Most certainly we ought to. And yet in close proximity to the lake no fragments were noted.”

What Dutton didn’t realize was that these fragments were quickly buried under massive pyroclastic flows, super-heated mixtures of rocky debris suspended in volcanic gases,  that raced down the broken slopes of the volcano. As these pyroclastic flows came to rest and cooled, they deposited layers of welded rock up to 100 meters deep around Crater Lake.

These vast deposits of ignimbrite have long since been covered by dense forests of pines, firs and hemlocks. Airborne Lidar instruments, which bounce laser flashes off the ground below, now make it possible to see through the tree cover and map the topography of the deposits in great detail.

More than a century after Dutton’s visit, Mount Mazama ash was identified in ice cores taken from Greenland’s ice sheet. From that and other evidence, scientists now estimate that the catastrophic eruption took place about 7,700 years ago. Dutton had figured it must have been “many thousands of years” in the past. The ice core evidence suggests that the volcano loaded the stratosphere with up to 224 metric tons of material, including 8 metric tons of chlorine capable of greatly depleting the stratospheric ozone layer. The haze would have lowered temperatures at mid to high northern latitudes by a degree or two for about three years after the eruption.

∞

Citation

Crater Lake, Oregon, a proposed national reservation by C.E. Dutton, Science, February 26, 1886