In the spring, when warming temperatures bring snowmelt and rainfall to the watersheds of frozen northern rivers, the flow of rising waters breaks up the winter cover of river ice and floats it downstream. Where these floes jam and raft up—often where the channel narrows—ice jams, or dams, may impede the flow of water until the river’s forcing pressure fractures and destroys the dam. The headwall of floodwater that bursts through and scours the banks for some distance downstream is called a debacle, a word often used in other circumstances to describe a similarly stunning mess.

Ellen Meloy