A powerful storm hit Libya’s northeast coast on Sunday. Two dams burst upstream from the port city of Derna, causing a torrential flood that has killed more than 5,000 people, according to local officials. … Derna is also built on top of an alluvial fan, a type of landscape formed at the base of mountain ranges by loose sediment washing down rivers and streams. These landscapes are known to be at risk of “ultrahazardous flooding,” said Brett Sanders, a professor of civil and environmental engineering at the University of California Irvine. When alluvial fans experience heavy rainfall, floods tend to strike suddenly, travel very quickly, and carry a lot of sediment and debris that can bulldoze whatever is in the way. [Subscription required, campus-wide access provided by UCI Libraries. Sign-up here: https://guides.lib.uci.
