Why are ice jams common in rivers that flow northward?

Ice jams are particularly common in rivers that flow northward because of the direction in which the spring thaw progresses. In these river systems, the upstream (southerly) reaches experience warmer temperatures first, causing the ice to break up and move downstream.12

As this ice travels northward, it encounters colder, more stable ice covers that have not yet begun to melt. Because the moving ice from the south meets this intact, downstream ice, it often exceeds the river's transport capacity, leading to the formation of an ice jam. This process can repeat multiple times as the thaw continues to move northward, often resulting in significant flooding as water builds up behind the blockages.13