Crater Lake is 592 metres of water standing where a mountain used to be, in the Cascades of Oregon, and it is the deepest lake in the United States. The mountain was Mount Mazama. About 7,700 years ago it emptied its magma chamber and the summit caved in, leaving a bowl that filled over centuries with nothing but rain and snow. No river runs in and none runs out. With almost nothing suspended in water that clean, there is nothing to scatter the light. What comes back at you is the deepest blue there is, and it richens as the sun climbs. The rim stands 300 metres above the surface in bands of red, grey and ochre, layers of the vanished mountain cut open by its own collapse. From one of those overlooks you get the clearest sense of how big Mazama must have been. Rim Drive circles the caldera for 53 kilometres, and every pull-off you stop at reframes the water.
At first light, before the wind gets up, the surface lies dead still and doubles the walls and the clouds into a single sheet. Wizard Island, the cinder cone that grew inside the caldera after the collapse, stands in the middle of it, though the boats across and the one trail to the shore are shut for repair until 2028. A full-size tree stump called the Old Man of the Lake has floated upright out there for over a century, drifting miles with about a metre of bleached wood showing. The Mazama newt evolved in this isolated water and has never been found in any other, and introduced crayfish spreading along the shore are now taking it apart. In winter some twelve metres of snow bury the rim, the road closes and the forest goes white, while the lake below stays an unfrozen disc of dark blue that you reach on snowshoes. The Klamath tell of a battle between Llao of the underworld and Skell of the sky that destroyed the mountain, and woven sandals have been dug out from under Mazama's ash, so somebody was here to watch it happen.