GREEN BAY, Wis. —
Ice jams can form almost anywhere that has winters cold enough for rivers to freeze—such as areas in the Northeast, the Midwest and Alaska.
Ice jams are caused by melting snow and ice, when temperatures rise above freezing for a sustained period of time. Thick ice sheets on rivers and streams can begin breaking apart.
Pieces of floating ice carried by the current can jam in tight or curved areas in the water. These jams can develop near river bends, tributaries, downstream of dams and upstream of bridges or obstructions.
Ice jams can be dangerous for people living in towns nearby. Because the river is blocked, the rushing water has nowhere to go and it can cause flooding in the surrounding area.
Some can even divert the flow of a river and cause major flooding.