Volcanic debris flows (lahars) in El Salvador pose a significant risk to tens of thousands of people as well as to property and important infrastructure. Major cities and nearly a third of the country's population are located near San Salvador, San Vicente, and San Miguel volcanoes. Debris flows traveling as little as 4 km from source at these volcanoes put hundreds to thousands of lives, property, and infrastructure at risk.

We used a statistically based model that relates debris-flow volume to cross-sectional and planimetric inundation areas to evaluate spatial patterns of inundation from a suite of debris flows ranging in...