Most people know that Yellowstone National Park is geologically active, but few realize that it sits atop a gigantic volcano. No one knows when it will blow next, but past eruptions have been huge, up to 2,500 times the size of Mount St. Helens in 1980. Today that would kill millions and change the worldwide climate catastrophically.

For now, we just have to wait — the problem is far too big for today’s engineers to tackle.