At the time my wife took this picture, I did not yet realize that we were walking around on an active volcano when we recently visited Yellowstone National Park. The outgassing behind me, which I had just walked through, should have clued me in, since it had a strong smell of hydrogen sulfide mixed with hydrochloric and sulfuric acids. At a gift shop, I found a book by Greg Briening called Super Volcano: The Ticking Time Bomb Beneath Yellowstone National Park. It explains the science of Yellowstone, and makes a strong case that the volcano that created Yellowstone will blow up again, possibly soon, with cataclysmic consequences worldwide.