Permafrost, the thick layer of perennially frozen ground that covers much of the Arctic, slows down the migration of Arctic rivers, according to a new Caltech study. River migration is a common process in which a river's path meanders over time due to erosion of the riverbanks. This rerouting, which can also occur in sudden floods, poses a threat for many communities that live along and depend on rivers. The findings also have implications for how the Arctic region will be impacted by a warming climate as permafrost thaws over time.