The now nonexistent Mount Mazama was built layer by layer over the last half million years – similar to Rainier, Hood, and Shasta. Its activity culminated in a week long eruption which ejected ash and cinder until the magma chamber below had been sufficiently relieved of material and pressure.
Without adequate support from the partially drained magma chamber below, Mount Mazama collapsed vertically, falling by approximately a mile over an estimated 15 minutes.
This created a crater with gently angled outer slopes and a steeply cleaved inner wall. The volcanic layering within the former mountain was exposed, and the plumbing network of vertical magma tubes stand as weather resistant spires and columns.
The diagrams below illustrate the geologic progression:
There are no rivers flowing into or out of Crater Lake.
All the water it contains has accumulated through direct precipitation. Without significant turbidity due to river runoff and without significant aquatic life being introduced (there are crayfish, but they mind their manners), the water remains absolutely pristine. In 1997 Crater Lake set the world record for depth of clarity with a 142 foot Secchi disk (wiki) reading. But since visitors are not permitted to swim what’s the use of all that clarity? Answer: The rapturing beauty of its blue bluey blue-ishness!
Hiking within eyesight of the lake is limited.
There’s a rim trail around its perimeter, but the same general views are afforded by driving the rim road. I decided to hike Mount Scott to get an overview of the lake and its belt-line of cliffs.
From elevation it was apparent how much ash was still in the air. The Crater Lake fire, which started more than a month ago, was well contained but still smoldering. Evening approached and the atmosphere burned brown and orange. I descended Mount Scott, and drove to make dinner at the Skell Head overlook located on the east side of the lake. The settled smoke in the lowlands took on a cold maroon color before swelling as a streak of bruised purple.