Scientists believe a massive glacial dam release - or jökulhlaup - recently occurred in Southeast Alaska. But they probably would not have known about it if they had not been tipped off by an observant commercial fisherman.

A jökulhlaup flood struck West Iceland’s Hvítá river in the early hours of Tuesday morning when water from a lagoon by the Langjökull glacier suddenly broke a new path and flowed in a different direction. Thick glacial mud now coats the river banks, and much of Borgarfjörður fjord.

The National Weather Service has issued a flood advisory for Kenai Lake and the Kenai River near Cooper Landing.

Weather authorities and residents are getting used to responding to glacial floods in the Mendenhall Valley.