The location of a streambed drifts over time as the water carried downstream erodes the surrounding land. Sometimes that gradual process is superseded by an avulsion—an abrupt jumping of the stream from one channel to another. Avulsions are rare, typically happening once every few decades at most, but they’ve been linked to historical floods. The consequences were devastating for civilizations that relied on the crops destroyed by those floods. This photo—from optical data collected by some of the European Space Agency’s Sentinel satellites—shows the avulsion of the Pemali River in Indonesia. In 2006, almost 5 km upstream of the Java Sea, the river jumped from the longer right-hand path to the left-hand one.
Sam Brooke and Vamsi Ganti of the University of California, Santa Barbara, and their colleagues identified three categories of avulsions in a database they created from 50 years of global satellite imagery. The Pemali’s jump falls into...
