USGS Volcanic Ash page — information on how to cope with a volcanic ashfall.
Yellowstone Volcano Observatory — current volcanic activity at Yellowstone, updated monthly.
Yellowstone Caldera — Wikipedia page about the Yellowstone supervolcano.
Seismic Monitoring and Eruption Forecasting of Volcanoes — scholarly article on forecasting eruptions.
Supervolcano: The Ticking Time Bomb beneath Yellowstone National Park by Greg Breining. MBI Publishing, 2007. Provides an excellent overview of the history and geology of Yellowstone. Includes an account of major volcanic events that have impacted humans and speculates about the possible consequences of a Yellowstone supereruption.
Supervolcano: The Catastrophic Event that Changed the Course of Human History by John Savino, Ph.D. and Marie D. Jones. Career Press, 2007. Contains information on supervolcanoes around the world, including Yellowstone (Wyoming), Long Valley (California), and Toba (Indonesia). Chapter 10 is an interesting fictional account of a future supereruption at the Long Valley volcano.
Krakatoa: The Day the World Exploded, August 27, 1883 by Simon Winchester. HarperCollins, 2003. An exhaustive and beautifully written account of the biggest modern Plinian eruption.
Catastrophe: An Investigation into the Origins of the Modern World by David Keys. Ballantine, 1999. Describes how a volcanic event in 535 A.C.E. changed civilizations across the globe. Very useful for considering the possible political, social, and epidemiological consequences of a supervolcano.
Engaging but thorough analysis of why some societies fail. Also the reason I decided to include references to cannibalism in Ashfall.
Fascinating if obscure first-person account of the Mount St. Helens ashfall. It’s sobering to realize how terrifying just a few hours of ash-induced darkness were.
The best analysis of various communities’ reaction to real disasters I’ve found. Full of examples of sublime heroism, abject stupidity, and vicious brutality.