Twilight at Lake Yellowstone, Wyoming imaged by Michiel de Boer August 18, '08. Image ©Michiel de Boer.
A supervolcano is a few miles beneath the lake. A few miles above, the sky glows with sunlight scattered by ash and sulfate aerosol from volcanoes in the Aluetian Islands.
"Even on the way back [to Europe] in the airplane I could see it. It looked just like smog, but it seemed to be even higher than the airplane."
The high altitude volcanic ejecta produces glorious sunsets, rays and Bishop's rings.